CURRE {T STATUS of FREE .RADICALSAND LECTRONIC, LLY EXCITED METASTABLI / SPECIES ,Is HIGH Qergy Propellahts by Gerald Rosen Dr

1974009383

CURRE_{T STATUS OF FREE .RADICALS AND _LECTRONIC,_LLY EXCITED

METASTABLI / SPECIES ,iS HIGH _qERGY PROPELLAhTS

Gerald Rosen

Drexel University, Philadelphia, Pa. (NASA-CR-136938) CUERENI STATUS OF FREE N7_-17_96 RADICALS AND ELECTPONICALLY EXCITED HETAST_IE _PEC[ES AS HIGH ENERGY PROPEl_ANTS 7i_ "! Technical RePort Unclas (Drexe_ Univ.) 09 D HC $6.50 CSCL 211 G3/27 31[.71

Final Tech'%iual Report for project entitled Propulsion Applications of

Free Radicals and Elect lqnically Excited Metastable Species, NASA thru

JPL contract instrument_.

August 1973

(Revised December 1973 to include material suggesl by JPL staff members and literature Addendum)

Thlsw_l-kwls performedfor_ Jet Propulilm UI_M_, ¢lli_rnl Inl_tute of Ti_hnololY, ltillitl lY li Nition,I lelollliutlis llnd r_lliN Mmlnlltrstlmt _ .: ContiiGt !1A87,100,

Reproduction of this report in whole or In part is permitted for any t

purpose of the United States Government. 1974009383-002

_URRENT SIAr','S_OF FREE P_DTCAT_S AND ET,ECTRO._;IC-_.IEXCIT}ID.I,Y *

METASTABLE SPECIES /.S HIGH ENERC,Y PROPELI,ANTS i t Gerald Rosen i

Drexel University, Philadelphia Pa.

CONTE,VrS

I. Introduction ...... 1

2. Free P_dicals ...... 3

3. Metastables ...... 5

4. Theoretical Performance ...... 8

5. Manufacture and Storage ...... 13

6. Methods of Production ...... 13

7. Matrix - Isolation ...... 18

8. Current Experimental Work ...... 22

9. Alternative Proposals for Manufacturing H - _2 Propellants ...... 26

i0. Energy Release ...... 27

Ii • Recommendations for Future Work o%_o4eeepeoeeototo4eeeeoQe_eeeee.eoe4eee 31 *_

Summary ...... 32

Appendix A: Theoretical Specific Impulse Formula ...... 35

Appendix B: Local Heat Pulse Produced by a Chance Reaction of Free Radioals in a Hatrlx ...... _ ...... 37

Appendix C: Manufacture of an H -H 2 Solid Propellant by Ultra-Energetlc Hydrogen Atom Bombardmeflt ...... 38 t

Appendix D: Manufacture of an H - H_ Solid Propellant by Impregnation with Radioactive Phosphgrus ...... ,...... 42

Appendix E: Deflagratlou of an H - H2 Solid Propellant...... 44 1974009383-003

I. Introduction

Considerable interest has been attached to the research and develop-

ment of free radicals and electronically excited metastable species for

use in rocket propellants, because markedly superior performance is pre-

dicted theoretically for them. It is well-known that the maximum for

specific impulse with the best conventional chemical propellants is in

the neighborhood of 500 sac. On the other hand, values for the theoreti-

cal specific impulse in the neighborhood and even well above 750 sec are

predicted if it is possible to employ the m_-t promising free radicals or

electronically excited metastable species (i.e., "metastables"). Such a

50% increase in specific impulse would engender a dramatic concomitant

increase i_ payload and a decrease in the number of stages in space vehi-

cles (Carter 28, Wlndsor210).

This report provides an up-to-date survey study of free radicals and

electronically excited metastable species as high energy propellants for

rocket engines %. Included as free radicals in our study are nascent or

atomic forms of dlatomlc gases in addition to the highly reactive dia-

tomlc and trlatomic molecules that possess one or more unpaired electrons.

For use as a propellant, a free radical must be a stable (ground-state)

quantum mechanlcal structure and have a rather high energy of reaction

per unit mass, which implies that the free radical must be of relatively

low molecular weight. Electronically excited metastables of possible

interest as propellants must have sufficient resistance to spontaneous

electromagnetic decay (i.e., a sufficiently long radiative lifetime) in

addition to having a high specific energy content.

and vlbrationally excited molecular species, also of \ lchydrogen interest as possible high energy propellants, are not discussed in this report. A recent description of current experimental research on the production of mstalllc hydrogen has been given by Lub_i_ I19. Noteworthy experimental and theoretical r4sults on vlbratlonally excited hydrosen, oxygen, r . and other molecules have been obtained recent]$ and reported in Reds. 37, .:

39, 54, 55, 76, 103j 109, 123, 160, 182, 195 and 207. !i: ] 974009:388-004

2 'I

Free radicals and metastables that may offer possibilities as pro-

pellants are discussed in Sections 2 and 3. In section 4 it is sho_.m

that propellants composed of any of the free radicals H, N, O, CH, BE,

N'H, BH2, CH 2 or the metastables (Z3SI)He*, (2D)N*, (3P2,0)Ne_ , (3e2,0)Ar _

(ID)o*, (alAg)O2 * can give performance (predicted by the theoretical

specific impulse formula derived in Appendix A) superior to the maximum

attainable for O2-H 2 or any other conventional oxldlzer-fuel combination.

In particular, extraordinary theoretical performance is predicted for

atomic hydrogen, the C}!free radical, and the metastable excited states

of helium, nitrogen, neon, and atomic oxygen with H 2.

The essence of the manufacturing and storage problem is described in

Section 5, prior to the detailed discussions of methods of production in

Section 6 and matrlx-isolation storage in Section 7. It is shown in

Appendix B that a very small characteristic time is associated with the

heat pulse produced by a chance recombination reaction of matrlx-isolated

free radicals, and thus neighboring free radicals cannot absorb requisite

energy from such a heat pulse for escape from their trapping sites. Be-

cause the host matrix material will be vaporized along with product gases

during the energy release,the matrix-iso_atlon host species must also serve

as the working fluid for a free radical or metastable propellant, and a

decisive advantage is noted to accrue if the free radical or metastable can

be produced in situ from one of the matrix host species _2' N2' 02' He, Ne

or At. Deductive considerations show that among the propellant condidates

with this property, atomic hydrogen is an H2 matrix is most accessible to 1

near-term development with existing technology. [ A review of current experimental work related to the manufacture of an I i atomic hydrogen propellant is presented In Section 8, where the two main ' 1 t technical aids now being employed to achieve higher concentrations of reactive

r _ 1974009:388-005

species with matrix-isolation, the use of very low temperatures and very strong magnetic fields, are discussed in detail. It is sho_m that important progress t_ard the developnent of an atomic hydrogen propellant appears imminent with venerable methods of production and storage being augmented by these n__w technical aids. In Section 9 it is observed that the manufacture of an E-H 2 propellant, 15% atomic hydrogen by weight, may be possible by ultra-energetlc hydrogen ato_ bombardment of solid H 2

(theory described in Appendix C) or by impregnation of solid R 2 with radioactive phosphorus (theory sketched In AppendixD). The theoretical estimates presented in Section I0 show that matrlx-isolated free radicals or metastables must be used directly without prior melting as solid propellants. Finally, the steady deflagration of an H-H 2 solid propellant, 15% atomic hydrogen by weight, is analyzed in Appendix E.

2. Free Radicals

Quantum mechanical analysis shows that a host of free radicals are iikely to have adequate (ground-state) stability and sufficient specific [! energy of reaction to warrant further consideration as propellants

($chnelderman 170, Kepfordl07). The outstanding practical candidates

for free radical propellants are shown in Table I, In w'nlch the first eight

entrles, namely _, N, O, C"H, BH, _, B_ 2 and CH_,

are free radicals that have been studied experimentally for many years

(Pimente1157, Milllgan 134,137, Wlndsor 210, Ramsay 163) , while the last

three entries are the seemin_most promising additional free radicals that

have been conjectured to exist by quantum mechanical analysis, i "1974009383-006

FREE GROUND SPECIFIC ENERGY CKD_ICAL REACTION RADICAL STATE (kcal/_)

H 2SI/2 2H ---_ H2 52.10

N 4S312 2N ---_ N2 8.03

0 3p 20 _ 02 3.71

s lld CH 4Z- 2CH _ 2C(p_ase) + H2 i0.90

BH / 3IK 2BH ---_ 2B + R 2 6.19 !

N_ IA 2NP --_ N2 + H 2 5.25

BH 2 2A1 BR 2 ---_ B + "2 5.18

m c.2 3_g c.2-.-c (_R_)+"2 5.29

He20 1E+g 2.e20 ---_4He + 02 4.35

HLt IZ+ _ 2HLI "--_"2 + 2 Lt 5.46

H zLI 2Z+u H2LI _ H2 + Li 3.94

4 T J b

Table 1. Known and theoretieall7 conjectured free radicals that

may offer possibilities a_ propellants, t h 1974009383-007

There is no experimental evidence that the latter entrles, .amely

HeR0, ELi a._ HRLi , can be produced in sufficient amounts to be useful as propellants (KepfordI07, Henneker77), and since there is no

advantage that would accrue in greater specific energy from the use of

these latter entries, it is reasonable that attention in our survey should

be concentrated on the three monatomlc radicals R, N and O,

the three dlatomic radicals CH, BH and }_, and

the two trlatomlc radicals Bll2 and CH2.

3. Metastables

An electronically excited state of an atom or molecule is said to

be metastable if its radiative lifetime Is greater %hen a microsecond.

Assuming that it is not possible to suppress the spontaneous electro-

magnetic radiative decay of a metastable state#, propulsion applications

would appear to require radiative lifetimes of the order 103 sac or J greater. A llst of known metastables that offer even remote possibili-

ties as propellants is given In Table 2. Known metastables with radiative

lifetimes less than a millisecond or with relatively smaller values for

their specific energy [ - (excitation energy of specles)/(mass of specles), i . expressed in column five of Table 2 by using the molecular weight values ! and the units conversion formula_ I eV/partlcle E 23.0 kcal/ mole ] B have been excluded from a broader tabulation 01uschlitzl44).

, It has been noted independently by J, Zmuldzlnas and by the present writer that it may be possible to interfere destructively with the quantum mechanical : probability amplitude for spontaneous electromagnetic radiative decay of an \ i ofatocmicriticamletasatmaplbleitudestaatnde, wsayavelebngy timh poonsingmetaastsatbalendls ng-inwaavelatteleicec. tromaThgnee tictheorefielticald analysis required to establish necessary critical conditions would be a fund-

99, 111, 122, 214 and 215.

r amental extension t of the quanttmmechanlcal calculations In Reds. 17, 50, 41-45,

1974009383-009

In the absence of a conceptual scheme for preservin£ the shorter-llved

metastables, the electronically excited metastahle species of practical

interest as possible propellants are 23S I helium, 2D nitrogen, 3P2, 0

neon and argon, _ oxygen either with a nonreactive working fluid or

with H 2 "after-burnlng", and finally alAg oxygen with H 2 "after-burning"

(i.e., the propellant 0;-- H2).

In addition to the basic metast_bles discussed above and shown in

Table 2, there are hydrides and other low molecular weight marketable

compounds that can be made chemically by reacting (23SI)He * , (3P2,0)Ne*

(3P2,0)Ar* , (2D)N*, or (_)0" with ordinary (ground-state) hydrogen and

other low molecular weight atoms. Such electronically excited metastable

compounds have less specific energy than their metastable atomic progeni-

tors, owing to the energy lost in the formation of the chemical bond and

the greeter molecular weight of the compound. Nevertheless, a metastable

compound might be of considerable interest as a propellant if it were to

have a radiative lifetime much greater than its metastable progenitor.

Although one cannot prove a quantum mechanlcal theorem which demonstrates 1

that this could never be the case, it is unlikely that compound-formation

effects an increase in the radiative lifetime for spontaneous electro-

magnetic decay S of anymetastable (Freed 59, Bixon 9, Guberman 71, Sega1171,

# On the other hand, collisional reaction rates and decay rates associated with external electromagnetic perturbations can be suppressed by metastable compound-formatlon, as exemplified by the

(2381)He_ states (with observed lifetimes about 1.5 x 10"beet) and (a3Z:)--

He; states (with observed lifetimes _reater than 0.1 sec) produced in i electron-bombarded superfluid helium (see Refs. 40, $8, 75, 78, 81, 108, 184, 185). The radiative lifetime of a metastable for spontaneous electromagnetic d_cay provides a theoretical upper bound on the observed lifetime

of a metastable that under8oes collisional reactions and/or induced decay. _ _

...... Ji 1974009383-010

Rosenfield 165, Nesbet147). In fact, the _nterato_Cc Cou]on5 field felt

by a metastable atom in a compound molecule usually increases the rate

of electromagnetic radiative emlss_on by a factor typically of the order

104 , and hence the radiative lifetime of a metastable compotmd would

ordinarily have a magnitude less than the radiative lifetime of its ato-

mic metastable progenitor by a factor typically of the order 10-4 #.

Attempts to produce metastable helium hydride He H and, more recently,

the metastable compounds OIIe and ONe in significant amounts from

and for experimental applications have been un- (23S1)He * (3P2,0)Ne*

successful (Kepfordl07)#_ Likewise, it has not been possible to produce

end store electronically excited metastable states of free radicals in

significant amounts for detection (LlnevskyllS). Thus it appears moat

practical to concentrate future theoretical and experimental studies on

the Iong-llved metastables of helium, n_trogen, oxygen, neon and argon

that are listed in Table 2.

,, , # The interatomic Coulomb field felt by a metastable atom in a compound molecule generally has the order of magnitude of that due to a proton acting at a distance of several Bohr radii [_,t_-_)"in urd_ _._c-_ and _ e_/4",'_ (I_7)'*_• _" This leads to the formal replacement of a fine-structure constant _ by a number of the order unity in the matrix-element for the transition, when one alters the vertex of a Feynman diagram for spontaneous radiative decay to give a Feynman diagram associated with the inueratomlc Coulomb field decay (see, e.R., Ref. 50). Since the matrlx-element is thereby increased by a factor of the order 6¢"I , the radiative decay rate is increased by a factor of the order ¢<'_ N ]O e+ for the metastable atom in a compound molecule.

ttThese metastable$ are theoretically auto-ionizing states (Russek 167, Bhatta $, Miller lZg), and indeed experiments indicate that auto-ionization

'. is concomitant with the formation of helium hydr_$ (Neynaber 148) , the t dominant apparent process being He* + H2 --4= lleR + H + (an energett@ electron) with the resulting heH_ hydride ion unstable under subsequent electronic recombination.

,i .. j 1974009383-011

" 4. Theoretical Perfoz1_ance

For prescribed chamber conditions, nozzle _eometry, end chemical

composition of the exhaust gas, the theoretical perfomance of a pro-

pel_ant is indicated by theassociatedvalue of the specific impulse.

An approximate theoretical specific impulse formula for conditions typi-

cal of those that would apply for an advanced propulsion system onboard

a spacecraft (vacuum environment and essentially lossless isentropic

equilibrium expansion through a nozzle with an expansion area ratio of

60:1 and an effective constant specific heat ratio of 1.30) is derived

in Appendix A with the result given by (A.6),

l = 265(O/I kcal/gm)% sec, sp

where Q denotes the overall net energy release per unit mass of propel-

1ant. Assuming that the free radical reactions in Table 1 go to temple- % tlon and the metastable species in Table 2 are quenched completely to their

ground states, the energy release Q is given for any free radical or meta-

stable propellant by multiplying the specific energy in Table i or Table 2

by the weight fraction of the energized species in the propellant. Thus,

for example, in the case of H with H2 as the working fluid, an atomic by- !

drogen weight fraction of .20 (meaning one free H atom for every two R2

molecules) yields Q - 10.42 kcal/_ and Zsp - 857 sac, accordinE to the

approximate specific impulse formula above. Table S displays Q and Iep values calculated in this manner for the best conventional chemical pro-

pellants and the most promisin8 free radical and metastable propellants.

The weight fractions of the latter species are fixed at simple fractional values

that give performance at least comparable to that of conventional propellants, and

thus Table 3 shows the approximate weight "fractions required for practical

competitive usa of free radical and metastable propellants.

" 4 I 1974009383-012

PROPELLA21T WFIG}_ FRACTION OF Q I , sp I OXIDIZER OR FREE (kcal/_m) (sec) RADICAL i t

F2 ff2 .938 3.16 471 j I{ o032- _2F.2 .825.889 _.953.83 _56520 i / _ 1.000 52.10 1918

/inert worklng_ .500 26.05 1355 -Jfluid, e.E.,I .250 13.02 959 %_2 or Re / .100 5.21 606

CII-( " ) .500 5.z,5 62o

B}I-( " ) .500 3.I0 467 i N-( " ) .500 4.02 531 J

_, Nff-( " ) .500 2.62 430 B_2-( " ) .500 2.59 t_27 _2-( " ) _500 2.6a 431 i o ti,,e,'t,no,,_om-'% "[bustlble work-] .500 I.85 361 %Ing fluld /

!: k 0 - if2 .500 3.64 506 I

Table 3. Theoretical performance of the best conventional and the most promtsins

free radical and matastable propellants.

L 1974009383-013

PROPELLAh"f WEIGHT FRACTIO}:O_ q I sp METASTABLE (kcal/g_.) (see)

f(_3_1)_,_{fluid,/_ work_e.g., ] .S.100OO S711.4.o 28950o_ _H 2 or Be / .050 5.70 633

(2D)N*-( " ) .500 5.97_ 648

(3P2,0)Ne*_( ,, ) .500.250 4.9.5762 820580

__3,2,o)_¢-"c , ._oo 3.35 _6

I /inert, noncombus-_ (ID)o*- {tlble working / .500 3.26*+ 480 %fluld /

(ID)o* - _2 .500 5.05 597

(alAg)02* - H2 .825 3.53 _9_

Table 3 (continued). ! P

tlncludes 4.02kcal/_ resulting from the _round-state recombination 2_ ---,- _2

reaction that follows de-excitation. I _ ! *_Includes 1.8_ kcal/gm resulting from the ground-state recomblnac_on 20 --_ 02 reaetlon but no contribution from a conventional oxidation _sactlon. 1974009383-014

Since I is proportional to Q% and Q is directly proportional to the sp

weight fraction of the free radical or metasta51 species, it is a s_iple

matter to figure the I value for any propellant in Table 3 with an al- sp tered weight fraction value.

An inspection of Table 3 shows the extraordinary theoretical perfor- i i mance predicted for atomic hydrogen, the CH free radical, and the meta- !

stable excited states of helium, nitrogen, neon and atomic oxygen with H 2.

Performance superior to the _est conventional propellants is also indi-

cated for atomic nitrogen with a weight fraction of .5 (meaning one N atom

for each seven H 2 molecules if hydrogen is employed as the inert working I

fluid), while the free radicals BH, N'H, BH2,CH 2 and O would require weight i t fraction values in excess of .5 in order to surpass the performance of

the best conventional propellants. Because of the relatlve]y large mole- !

eular weights of 02, F2 and 03, an increase in specific impulse cannot

• be achieved by supplementing a free radical recombination that yields _2

as a product with a subsequent conventional combustion reaction (Windsor210). ) t,<

[ On the other hand, a significant increa_ in specific impulse is attainable } i

if the ground-state atomic oxygen recombination process, the _metastable

atomic oxygen quenching and recombination processes, or the alA molecular I ! g I oxygen quenching process is supplemented by a conventional combustion re-

! action with H2, as shown by the illustrative entries in Table 3. The para-

£; mount issue is whether free radical and metastable propellants can be I

manufactured, stored, and used in practice in the required concentrations

and amounts _or rocket propulsion. 1974009383-015

5. Manufacture and Storag_

Free radicals and metastables are produced by a large variety of

physical and chemical molecular dissociation and electronic excitation

reactions. Except under rather special conditions, however, such reactive

species cannot be produced in high concentrations and/or in large amounts,

as required for propellant manufacture. Moreover, for tle storage of

highly reactive free radicals and metastables only one effective method

is known, the so-called matrix-lsolatlon technIRue in which the reactive

species are trapped as isolated entities in an inert solid at a cryogenic

temperature. Free radicals and metastables produced in a gas or ]lquld

must be rapidly condensed and trapped by being frozem into normal or inter-

stitial sites in an inert cryogenic lattice, while immediate storage of

the species may be afforded by so-called in situ production methods which

involve dissociation or excitation processes that take place exclusively

within a pre-formed matrix.

In the sections which follow, the methods for production of the re-

active species and storage by the technique of matrlx-isolation are re-

viewed and considered from the standpoint of rocket propellant requirements.

Despite the fact that no free radical or metastable propellant has been

manufactured and stored in a practical quantity to date, the survey pre-

sented here shows that important progress appears imminent with the venerable

methods of production and storage being augmented by new technical aids.

Xndeed, the odds appear to favor the successful manufacture, storage, and

usa of an atomic hydrogen propellant within the present decade, i I ! 6. Methods of Production !

Table 4 provides a list of _ethods that have bean used to produce free 1

radicals and metastab!es in gases, liquids, and solids.

L 1974009383-016

lJ,

METHOD OF REFEP_,_CE$ FOR FREE RE_FPJ?.:CES FOR PRODUCTION RADICALS METASTABLE_

PHOTOLYSIS: 189, [157], [130--138], 149, [118], [125]

VISIBLE OR ULTRA- [93--96], [164], [176], VIOLET RADIATI_ i, 47, 73, 79, 151, 158, 159, 187

X-_YS [157] [125]

U-RAYS [157], [21], [202], 196

ELECTROMAGNETIC 172, ll, 12, 16, 19, 51, 145, 181, 118 DISCPARGES 56, 57, 146, 150, 26, 80, 72, 200, 211

THE_t%L_TFODS 189, 25, 137, 179, 51, ]21, 82, 3, 118 177, 18, 38, 205, 206

CI{_RGE TP.rC:SZER 145, 46, 201, 5,

PROCESSES 53, 178

FLECTRON _.mACT [157], 203, 15 [125], [I18], 191-193, 2,12 ,n5,29-31, li 183-185, 81, 83, 40, i 58, 13, 203, 15, 75, 106, 108 145, 179, 209, 204, 62, _3, 34, 69

ATOM & _mLECULE [157] 86, 186, 82, [125] BOMBAPJ)ME_T

T_b]e 4. Methods of production of free radleals and metastables. Squsre brackets

q denote in situ production references, while all other references describe

production in a gas or l_quid. 1974009383-017

Most useful for basic scientific investigations in which small quantities

of the reactive species are adequate, the very controllable method of i

photolysis utilizes visible or ultraviolet radiation produced by a high- t intensity flash, an arc light, or a laser of suitable wavelength (belov

the dissociation or close to the excitation wavelength of the species). I

In photolysis, a so-called precursor species undergoes dissociation or !

excitation with the absorption of quanta in the intense radiation, there- i by yielding the free radical or metastable (in the gas phase or in situ f

through an inert solid matrix at a cryogenic temperature, in usual appli- |

cations). The method of photolysis cannot be employed for the production J of large amounts of free radicals or metastables, as required by propul- I sion applications, because of severe limitations in the amount of energy f

that can be communicated to a medium by devices that emit visible or ! ! ultraviolet radiation. For example, a power level of the order of I051.'is k

required to energize reasonable amounts of solid B2 to a useful H-H2 pro- I

pellant mixture in a reasonable time (see Appendix C); such a required power

level is several orders of magnitude above what can Be delivered By a laser i

that emits radiation having a wavelength less than .276 _m (the threshold I_ f for dissociation of H2). } ! Less developed than photolysis is the use of higher energy electromagnetic quanta, x-rays and _-rays, which must effect dissociations and

electronic excitations primarily through intermediate absorption processes.

Although x-rays and _-rays allow for in situ production of the reactive

species, the effective absorption cross-sections are small for light-atom

solids and thus the higher energy eleetromaBnetlc quanta are not attractive !

energy sources for the manufacture of large amounts o_ free radical or \ metastable propellants. 1974009383-018

Electromagnetic discharges (microwave, rad_ofrequency, etc.)and various

thermal methods have been used widely for the gas phase production of free

radicals and metastables. These methods are capable of producln_ free

radicals and metastables 8t sufficiently high rates in the gas phase for

possible use in the manufacture of practical amounts of propellants. In

particular, free radicals can be produced copiously with glow discharses

at low resultant temperatures which facilitate the required rapid conden-

sation and trapping of the gas discharge in a cryogenic matrix. _owever,

electromagnetic discharges and thermal methods are not applicable to

in situ production and the more efficient concomitant trapping of the

reactive species. Likewise, charge transfer processes, as exemplified

_e_ by the helium ion reaction _e++ _e (23Si) + He+ , have been found

to produce metastables copiously under suitable conditions in the gas phase

but not in a solid matrix.

Most premising for the production of free radicals and metastables

in the amounts required for propellants are electron impact techniques.

The latter are effective for copious production in sltu in a cryogenic

matrix as well as in a cryogenic liquid, in a gas, or In (transverse bom-

bardment of) a_um and molecular beams. For in situ production of reactive i

species propellants by electron impact, it Is necessary to generate free +

electrons in quantity throughout a matrix (see Sections 8,9 and Appendices

C, D), because even very energetic electrons have a very short range in a

solid (e.g., an "_ectronwith an inital kinetic energy of I MeVwill pene-

trate a distat_ceof only about (0.4 p;m/cm2)/_,_ere _ is the density of

the solla). t t ,, ,- L t A RigY_-e_rgy beam of electrons might be employed to energize thin wafers of a 1 matrlx.lna manner similar to the hydrogen atom bombardment in Appendix C, but power+delivery and charge-accumulation considerations favor neutral atom bombardment of a wafer.

i 1974009383-019

Methods for the production of reactive species _n situ by atom and molecule bombardment appear to hold considerable promise in theory, but still _"have not been Investigated with appropriate experimental research programs. At high energies for the atoms or molecules in the _eam, secondary electrnns will be produced via ionization processes in the matrix and assist in the production of reactive species by electron impact reactions (e.g., see Appendix C).

All of the free radicals and metastables _hat appear in Table 3 have been produced in high concentrat!ons by one or more of the methods in

Table _. Specific references for the efficient production of H, N and O are given in the review artlcle by Carstens eta]. 27, for the production of OH, BH, N}I, BH 2 and CH2 in the revieu articles bY Milllgan and

Jacox IS4'135'137 and Ramsay 163, and for the production of the metastables

(23SI)He _, (2D)N*, (3P2,0)Ne* and Ar * , (ID)o* and (alAg)02 * in r the review article by Muschlitz 14_. Moreover, the methods of production for the latter reactive species appear to be readily adaptable to scale-up and large-quantlty manufacture. In fact, production efflciencies can be expected to improve wlth scale-up and the increase in volume-to-surface- area raties, owing to the suppression of surface recombination and quenching reactions. Therefore, the essential problem is the stabilization and storage of the reactive species by matrix-lsolation.

196o i ..tel =o=e 157p,.I09)= ote=tlalltlesandl Ita-

ttons o_ atom bombardment are virtually unexplored.... The technique surely t deserves continued exploration". ¢ 1974009383-020

18 }

7. Matrlx-lsolation

Important technical advances with the In situ and gas condensation applications of the matrlx-isolation technique have been made in recent years by Pimente1157-159, Weltner 205'206 , Milligan 130-138 , and Jacox 93-96 .

Since the host matrix material will be vaporized along with reaction product gases during the energy release (see Section I0), the host species i must also serve as tlleworking fluid for a free radical or metastable I t propellant. Substances which have been used effectively for matr_x-isola- I ! tlon of highly reactive species and have low molecular weights are H2,N2, ? 02 and the lighter inert gases He, Ne, Ar. The latter candidates for the ! I dual role of matrix host and working fluid appear in Table 5 with the temperature values required to maintain the solids at prescribed vapor pressures (data extracted from Ref. 125, p. 192). With the exception of ! helium, all of these substances are solids that have molecular concentrations close to .045 moles/cm 3 at temperatures less than 4°K. i

Notwithstanding intensive development and applications of the techni- i que, it has not been possible to secure a reactive species concentration greater than about 1% molar # in a matrix by the now ve=erable In sltu and ; gas condensation methods Of trapping with temperatures of the solid as low !i as 4.2°K (Fontana 56'57, Wall 202, Broom 21, Windsor 211, Fire 51, grackmann 16,

LinevskyllS). !

#The molar concentration of about I_ was obtained for the free radical NCN

in an argon matrix by Milligan IS0"132 with _n s%tu flash photolysis of the

precursor species cyanogen azide, N3CN. Also see Ref. 157, p. 106.

4.- ,i 1974009383-021

19 1974009383-022

A principal difficulty that prevents the achiev_en_ Qf higher free radical and/or metastable concentrations is the imperfect isolation of free radicals in the direct deposition of a _as mixture or the imperfect isolation of precursor molecules for in situ production(Pimentell61)# .

Another reason why hi_her concentrations of reactive species have not been secured with direct deposition methods is that solids formed from a gas by rapid condensation at a very low temperature (i.e., less than 1/2 the freezing point of the substance) have defect-laden crystallineor amor- phous structures which favor the loss of reactive species by diffusion away from trapping sites (Pimentel157) inhibit the cooling of addi- Œ tlonal condensed layers because of relatively poor thermal conductivity

_indsor211'212). A decisive advantage accrues, therefore,if the free radical or metastable can Be produced in sltu from one of the matrix host species in Table 5 after a nearly perfect lattice structure has been formed By gradual cooling to a very low temperature. Moreover, the exceptionally high thermal diffuslvlty of such an ultra-cold lattice makes it possible to control the thermal slde-effects of in situ production,

SA systematic experimental investigation aimed at identifying precursors which isolate themselves preferentlall_ (prior to in sltu reactive species production) has not been performed to date, however.

t_The critical temperatures _or the escape of atoms from traps in a rapidly formed (Imperfect) lattice generally lle In a band from about I/7 %o 1/2 of the aubstance's _reezing point, thus from about 9°K to 32°K for N in

N2 and from about 2°K to 7°K for R in H2 (see _e_. 157, pp.7S-FS). Yet a nea_ly perfect lattice _ormed by _radual cool_tg o_ the substance, so_e- what higher values _or the bands o_ critical temperatures are indicated, t 1974009383-023

which might otherwise nullify the trapping effectiveness of a matrix with

local heating that promotes the escape of reactive species from trappln_

sites. Those free radical and metastable propellant candidates in Table

3 which can be produced in situ from matrix host species in Table 5 are

atomic ground-state hydrogen, atomic ground-state and 2D metastable

nitrogen, atomic ground-state and _ metastable oxygen, 23S1 metastable helium, 3p 2,0 metastable neon and argon and molecular alAg oxygen. Since practical competitive weight fractions (see Table 3) for ground-state 'y or 2D metastable atomic nitrogen are unlikely to admit stabilization in

an N2 matrix under the most favorable conditions (see Section 8), ground-

state and 2D metastable atomic nitrogen mlgbt be precluded as a prime

candidate. The requirement of a radiative lifetime greater than 2 hours

would preclude the metastables of atomic and molecular oxygen and very

probably the metastables of neon and argon as well_. Finally, the severe

technical difficulties involved in maintaining helium as a solid (see

comment in caption under Table 5), and perhaps also the limited availa-

bility and high cost of helium (_,,$351kgm) might preclude the helium

metastable. Our prime candidate for a propellant is assuredly ground-state

atomic hydrogen in an H2 matrix. ! , i Particularly s,oteworthy, the very low concentrations of reactive

species obtained experimentally with venerable matrix-isolation techniques

are well below what is predicted to be attainable by theoretical analysis t that assumes an ideal lattice and the random static isolation of free radi-

cals, subJeot to the proviso that two adjacent (nearest-neighbor) trapping

_a obsezved _£etima of a matr:_-£solated ,ataetable speo£es can be con-. stderably less than the (vacuum-isolated) radiative lifetime because of the pertts_ng influenoe of the lattice (see Ref. 89, pp. 329-334).

, _ 1974009383-024

sites cannot both accommodate reactive species (Jackson89'90 | Golden70

Chessin32). Accordin_ to such theoretical _nvestlgations of the problem,

mole fractions in the neighborhood of 15% should be attainable with a

nearly perfect lattice structure, in sltu production, and ideal isolation

(that admits only nearest-nelghbor recombinations). However,

Jackson91 has given a dynamical stability analysis based on a phenomeno-

logical continuum model which appears to indicate that local

heat diffusion from a chance reactJon of a pair of free radicals (e.g.,

H + H _H 2 or N + N --_N2)ma7 limit stable matrix-isolated concentrations of reactive species to less than about 2 or 3Z molar. It is sho_m in

Appendix B that Jackson's model leads to a characteristic heating time of

the order 10-14 sac if the matrix is maintained at 4°K or at a lower

(realizable) temperature. Clearly, free r_dlcals in the vicinity of a

reacting pair cannot absorb requisite energy and escape their trappln_

sites during the very small characteristic time associated with a heat pulse

in a matrix at 4°K or at a lower temperature. A quantum mechanlcal treat-

ment of the trapping stability problem, which takes account of the discrete

character of particle and energy transport processes, would be of consldera-

ble interest and Importance.

8. Cu_rentExperimentalWork

To achieve the hiEher concentrations of free radicals and/or metastables

required for useful propellants, it appears necessary to augment the vane- ,.

table matrix-isolation method with sunplementary technical aids that assist i in the stabilization of the reactive species. Two main supplementary tech-

nical aids are now being employed in experiments, namely, the use of very

low temperatures (in the range O.l°K to 1.5°l_produoed by advanaed etTogen_e

apparatus and the use of very stron_ magnetic fields (in the range 50kO to

lOOkO)produced by supereonduetin_ magnetS. At temperatures below 1.5°K, 1974009383-025

, : ...... |

.. one can expect a dramatic improvement in the trapping effectiveness of

a matrix competed to what it is at 4.2°K, the liquid helium temperature

of earlier matrlx-lsolation experiments. In partlcular, for hydroRen

atoms in a nearly perfect II2 lattice, the lower edge of the band of critical temperatures for the escape of atoms from traps Is somewhat greater

than 2°K, which implies that the trapping processes should proceed

favorably at temperatures below 1.5°K. Very strong magnetic flelds can

saturate the alignment and make parallel the spire of unpaired electrons

in free radicals, thereby inhibiting radlcal-radical recombination re-

actions.

The use of strong magnetic fields to assist in the stabilization of

matrlx-isolated free radicals is not a new idea (see, for example,

JonesTM _Tindsor2102,11 Fite51, Bracknann16) but only recently has the

cryogenic and superconducting magnet technology been available for the

attainment of conditions favorable for the stabilization of atomic hydro-

gen, according to quantum mechanlcal theory. Table 6 shows the low tempera-

ture-strong ma_netlc field combinations predicted theoretically (Re_. ].04,

po 25) to yleld substantial saturation_ of electron spln-allgnment in ato-

mic hydrogen and thus to i_hlblt the recombination reaction 2__ 2 (with only a total electron spin zero bound-state admissible £or molecular J hydrogen). Eowever, the combinations of low temperatures and strong meg-

" netio fields in Table 6 are neither necessary nor suffi_ient, for atomic

tPor free hydrogen atoms at temperature T in a strong magnetic field of magnitude B, the recombination rate is suppressed by the Boltzmnnn probability factor for non-alignment of the electron spin in a hydrogen atom, given by e"2_B/kT where p/k t l°K/15 _ is the spin-magnetic moment of an electron divided by Boltmann's eonst_at. The values in Table 6 obtain if the probability factor is required to equal _5 x 10" _ a number

i that makes the lifet_a_ of the atomic hydrogen sufficiently long for . _f practleal utilization (Ref. I04), ' 1974009383-026

I TEMPERATURE 2 1 0.5 0.1 [ 0.05 (°K)

MAGNETIC 570 285 142.5 28.5 14.25 FIELD (kC)

Table 6. Combinations of low temperatures and strong magnetic fields predicted theoretically to stabilize atomic hydrogen by nearly co:_- plete alignment of electron spins.

hydrogen trapping in an H2 matrlx_rlll assist stabilization, while the small interaction between the maKnetlc dipoles associated with the elec-

tron and proton spins in a hydrogen atom (JonesTM) and electron-spin

multipole radiative transitions(Hizushlma139) may promote recombinations

by electron spin-flips _n the course of interactions between atoms with

electron spins parallel initially. The rate of the latter phenomenon

is quite difficult to estimate for electron spin-al_gned hydrogen atoms _n

an n2 matrix+. Exciting posltive experimental results for atomic hydrogen stabiliza-

tion have been reporte& recently. Xn a painstaking research program,

Hess 80 has produced significant concentrations (apparently about 10_ molar)

of atomic hydrogen in the mak_x-isolate.l condensate from a hydrogen glow

discharge cooled very rapidly to about 1.3°K in a maenetic field of appro- _+ xi_ately 50kG .

+The required quantum mechanical calculation would have features in common with the analysis reported in Ref. 156.

_+Reas $0 has conjectured that large clusters of spln-aligned atomic hydrogen may .havefor_e_ an4 precipltatad out in the condenoat6 as a_r_Ic hv_rcgen domains, but this seems unlikely in vi_ o_ re_ent theoretlcal estim_t_ made by Etters_

A A 1974009383-027

I A copy of the Hess apparatus has been constructed at NASA's le_;Is_e_earch

Center and experiments now in progress will clarify the effectlvenes_ of

this method for atomic hydrogen propellant manufacture and storage. In a i

thermal sensing experiment, a mixture of H and H2 (or dissociated and molecular deuterium) is deposited on a nearly thermally isolated collector !

at about 1.2°K In a magnetic field of 100kG; the recombination of atomic i hydrogen _s induced by electrical heating and the energy release is mea-

sured by a car_on thermometer. In a mass spectrometer sensln_ experiment,

the bec_ of particles from either the H-H2 source or the collection region is chopped by a toothed wheel and phase-sensltlve detection is possl- blewlth an In-llne-of-slght quedrupole mass spectrometerwhich is capable of recording particles with molecular weight I. _esults from t'ese expe=i- mentsare expected to be availabl_ later this year (Broom22).

Work in progress will also determine the e_ectlven_s of internal in slt._ufreeradical production at ultra-low temperatures in a strong magnetlc field. Rare the idea is to use the _-ray electrons emitted in the decay of ! tritium to produce atomlc hydrogen by electron impact. In experiments now ! being performed at L_wls Research Center, ordinary _2 (molecularweight 2) i and trltlt,,_olecules (weight 6. hal_-llfe 12.26 years, mean energy o_

B-ray electrons 5.7 keV) are frozen toEether in a dilution refrigeratoF t at 0.1°K end a 35kG magnetic field is applied to the s_ple, thus provLdtng t very favorable conditions for stabillzln_ R atoms that result principally J from secondary electron impact dissociations of R2 molecules in the matrix

(see Appendix D). _teasurementof the atomic hydrogen conce_tratlon is accomplished by determining the magnetic susceptibility of the solid. This experiment will also yield results presently (Brown22). t 1974009383-028

9. Alternative Proposa!_ _or 'fanufacturi!Ign-l{2Propellants

In addition to the methods of manufacture and storage of an atomic hydrogen propellant that are under current investigation, there are two alternative sober,as which also mppear to w_rrant experimental study. The first involves the use of a cyclotron to produce a I0 MeV hydrogen atom beam which bombards solid H2 at a temperature below l°K in a very strong ma_netlc field. This possible method for the manufacture of an T_-ll2 propellant (about 15% atomic hydrogen by weight) has been worked out in a ! preliminary theoretical fashion by the present writer and is described

I here in Appendix C. The second scheme involves the use of the radionuclide p32 (with more than 300 times the specific activity of tri=!um) i to produce an E-If2 propella_t through secondary electron impact dissociation reactions. Secondary electrons will be proliferated by _ray electrons (mean energy 690 keV) in an H 2 matrix iv.preg_ated with .002% molar p32 atoms, and co2dltlons xrill be favorable for the trappln_ of free hydrogen atoms that result from H2 dissociations if the solid is malntalncd below l°E and a strong magnetic field is applied during the radioactive "curing" of the propellant. Essentially an extension of the tritium _-_2 propellant concept to higher energetlcs and production rates, this possible method for the manu£acture of a _-R 2 propellant (at least 15_ atomic hydrogen by i I weight) has been sketched by the present writer in Appendix D. Both of l these two schemes offer promise of providing an atomic hydrogen free radical : _ propellant that will yield a specific impulse of about 740 sec for rocket englnecondltlons that make formula (A.6) applicable.

J 1974009383-029

i0. Energy Relea_"

For all of the highly energetic free radical reco;nblnatlon reactions

in Table i the activation energies are close to zero, and these reco_iH-

nation reactions proceed rapidly even at cryogenic temperatures if the

species are mobile in the gas or liquid phase (Simha 174 Adrian l) Accord-

Ing to elementary collision reaction theory, the rate of such a free radi-

cal recc_Inatlon reaction is given by f m _ n v where _ is the velocity-

averaged total cross-sectlon for the reaction, n is the concentration of 1 I the free radicals, and _ is their mean velocity in the gas or llquld. Now i the cross-sectlon _ is certainly greater than 10-18 cmZ for the radical- J

radical reactions of interest at low energles_ and it is required that n

be greater than 1021 free radlcals/cn3 for a useful propellant in the stored

(matrlx-lsolated) cryogenic solid state. Thus, if a cryczenlc solid con-

taining trapped free radicals were to melt and attain a temperature of, ssy,

30°K and an associated mean particle velocity _ > i0 _ cm/see, then the

characteristic time for the free radical recombination reaction would be

f-i ffi(_ n _)-l < 10-7 sec. Quite clearly, in a time less than a tenth of

a microsecond Itwould not be possible to pump and utilize the free radical

mixture as a liquid propellant. Hence, it is necessary to use matrix-

isolated free radicals dlrectlywlthout prior meltlng as solid propellants.

The necessity of using matrlx-lsolated metastables as solid propellants

can be established by an argument similar to the one given shove for free

radicals. Electronically excited metastable species can react chemically or

_Two'ordera of magnitude larger than the conservative general lower bound

evoked hare, the total cross-section for the reaction H + H"_H2 is about 1.1 x 10-16 cm2 at thermal energies (_ 0.5 eV)_ with account taken of the i fact that the reaction proceeds only in the totel electron spin zero charms!.

I eW ' _ ' I 1974009383-030

undergo an inelastic collision with vlrtual]_ any atom or =_olecule, In- cluding the inert gases in their ground states• Three types of colli- J t sional quenching or de-excltation processes are possible: (i) colllsion_] I processes leading to thermal (increased molecular translational energy) # or radiative release of the metastable species excitation energy (see Refs. I

23,24,49,68,105,110,I14,124,1_2,144,145), (2) ionization reactions (see Refs. !

4,20,35,85, 87, _8,113,128,144,154,162,180,188), and (3) excitation i transfer reactions (see Refs. 68,112,166,173). The cross-sectlons for all I of these reactions are large, typically of the order 10-15 cm2 at low to ! ! moderate particle velocities. Although the latter ionization and exclta- I tion transfer reactions do not in themselves effect the release of exci- i tation energy in thermal or radiative form, the products of the latter i reactions quickly undergo subsequent electronic recombination and energy- i liberating colllsional processes at the high species concentrations of interest. Thus, if a cryogenic solid containing a useful concentration I of trapped metastables were to melt and attain a temperature of,say, 30°K, the characteristic time for overall effective quenching and sensible j energy release would be of the order or less than about a nanosecond, pre- cluding use of a cryogenic solid containing metastables except directly as a solid propellant.

_gnltion of a free radical or metastable solid propellant can be accom- • plished by any means (electrical or other) that warms a surface layer of the cryogenic matrix to a temperature at which the rate of heat release from recombination or quenching of the reactive species exceeds the rate of t heat loss by thermal diffusion. Centrally, this will be the case if a surface layer of millimeter thickness is maink[ned above the critical ten- 1 perature for significant escape from trapping sites (expected to be in the

J 1974009383-031

vicinity of 4°K for hydrogen atoms in a well-formed H matrix) for a 2 time of the order of a _lilllsecond. Because r,etastable species can also

be quenched efficiently by suitable static electric fields or By elec-

tromagnetic radiation of appropriate wavelength (see Refs. 17,84,99,]11,117,

141,155,214,215), more controllable nonthermal ignition systems are coe-

celvable as alternatives for metastable solid propellants, i Under proper conditions, the deflagratlon that follo_s iFn_t_on of a

free radical or metastable propellant can be expected to be steady and I i

stable_albelt very rapid, with the recombination or quenching reaction !

taking place a_ost excluslvely in the fluid (very light liquid and _as) I

adjacent to the melting surface of the solid matrix. An elemental volume Z

of the solid will be warmed to the melting point in a tlne much less than

a microsecond, a duration too brief for reactlwe species to ,bsorb energy,

escape from their trapping sites, d_ffuse through the sol_d a_d undergo i

reaction. Heat transport into the interiors of the matrix will be restrained $ because the solids of interest have thermal dlffuslvltles which decrease o rapidly with increasing temperatures above 1 K. For example, the thermal

dlffuslvlty of solid hydrogen is given approximately by (Ref. 36, p.13)

D=I.5 x 104 x (exp - T/.845°K)cm2/sec in the temperature range 4°K _ T _

12°K and remains of the order 102 cm2/sec (with roughly proportional decrea-

sing thermal conductivity and specific heat) as the temperature decreases 2 from about 4°K to below l°K. Moreover, because the solids of interest are

8enerallytra.sp_a.t to the bulk of electromagnetic radiation in the infrared

and visible wavelengths, the absorption of radiation emitted by hot ga_ in

the chamber is not expected to produce a sisnificant temperature rise in the

depths of the solids. \

J ml I IPlll i .m IL!i I 1974009383-032

Straight-fo_:ard order-of-magnitude considerations sho_' that the

burning velocity of a free radical or metastable solid propellant (i.e.,

the rate of llnear regression of the melting surface) will be determined

by the heat flux from the hot fluid to the surface via the equation AT _ --_ V s as h t

where X is the thermal conductivity of the liquid at the me]tin_ point

(surface temperature) of the solid, AT is the t_nperature rise in thc

fluid in a small distance 8x (of the order of the local mean free path

for molecules in the fluid) measured from th= surface, _ is the burning S

velocity of the solid, Ps is the density of the solid, and h L is the en-

thalpy zequlred to warm and melt a unit mass of the cold solid. The def]-_-

gratlon of an _-H2 solid propellant (15% atomic hydrogen by weight) is dis-

cussed quantitatively in Appe6dlx E, where the steady-state burn_g velocity

V = 2.1 m/sac is predicted for the propellant at a chamber pressure of s p - i00 psia. As sho_m by the analysis In Appendix E, the heat fli= to the

solid is moderated by the large velocity of the fl_ and the rapid expan-

sion of the fluid with heat release from the recombination reaction.

In the handl_ng of a free radical or metastable propellant, careful

precautions must be taken to insure that a sufficiently low stabilizing tem-

perature (augmented by a sufficiently strong magnetic field, in the case of

a free radlcal propellant) is maintained uniformly throughout the matrix at

all times. It is also clear that contact of the solid _ropel]aut _ith any

material which might catalyze energy release or absorb the reactive species

from the matrix must be avoided. For example, it is kno_m that platinum,

nickel and certain other metals can catalyze the recombination of atomic

hydrogen at low temperatures. Moreover, at__ichydro_en Is absorbed readily

J at I it I it I 1974009383-033

by and diffuses interstitially through virtually all ferrous alloys in

contact with molecular hydrogen (_mlalowsk1175, InterranteS_ with the dis-

sociation H2--_2H catalyzed at any hydrogen-steel interface, and it may

not be possible to contain an ultra-cold H-H 2 solid propellant in a hiEh-

strength steel casing. Solutions to the handling problems associated with

free radical and metastable solid propellants should be obtainable by per-

forming systematic experimental research with sample quantities of the

cryogenic solid propellants.

ii. Recommendations for Future Work

The following problems are of prime importance and worthy of detailed theoretical analysis in the near future:

_I) A quantum mechanical treatment of the trapping stability problem

which takes account of the discrete character of particle and energy

transport processes in a matrix.

(2) The s_ecializatlon of (I) for atomic hydrogen in an H2 matrix, extended

to include the quantum mechanical effects of a superimposed strong

magnetic field on the stabilization at very low temperatures.

(3) The extension of (2) to include the effects of heat transport into a \

pre-stabillzed H-H2 propellant that undergoes surface deflagratlon, i

It is reconnnended that the current atomic hydrogen experimental program at

LRC be expanded to include other basic experiments which will provide data for testln_ the theoretlcal results of (2) and (3).

• j I mm W ! I 1974009383-034

Propellants composed of any of the free radicals H, N, O, CH, 9H,

NH, BH 2, CH 2 or the metastables (23SI)He* , (2D)N*, (3P2,o))Te*, (3P2,0)Ar*. (In)o*, (alAg)02 * can, in theory, give specific impulses well above the

maximum attalnabSe for 02 - H 2 or any other conventional oxidlzer-fue] com-

bination. In particular, extraordinary theoretical performance is pre-

t dieted for atomic hydrogen, the CH free radical, and the metastable excited t!

states of he]i_m_,nitrogen, neon, and atomic oxyFen with H2. Il

A large variety of molecular dissociation and electronic excitation I

reactions can be employed to produce free radicals and metastables in Fases, I

liquids and solids, but the reactive species cannot be produced in h_zh

concentrations and/or In large am.ounts except ueder rather special cond_tlons.

Moreover, there is only one method knot_L to be effective for the storage of

these reactive species, namely, matr_x-lsolatlon. In the latter technique,

! the reactive species are trapped a_ isolated entities in an inert solid at

a cryogenic temperature, either by zapld condensation of a gas mixture or

with in sltu production in a pre-formed matrix by electromagnetlc quanta or

energetic partlcle bombardment. Although no free radical or metastable pro-

pellant has beau manufactured and stored in a practical quantity to date,

important progress appears imminent with the venerable methods of productlon

and storage being augmented by nm_ technlc_l aids.

Electromagnetic discharges and various thermal methods are

capable of producing free radicals and metastables at sufficiently high

rates in the gas phase for possible use in the manufacture of practical

amounts of propellants, but these methods are not applicable to in sltu \ production and the more efficient concomitant trapping of the r,'mctive

species. Particularly ef_ectiva for the production of free

J ' ' _ ' " m 1974009383-035

radicals and metasta_les lu situ, electron _pact techniques _re most pro-

mis!ng for the manufacture of reactive species propellants. The short

$ range of energetic electrons _n a solid requires that they _e _enerated in

quantity throughout the _atrlz. Methods for the production of storable {

! reactive species in situ by atom and molecule bon_ardment also hold consi- {

derable promise and warrant future experimental study, i

Since the host matrix material will be vaporized along x_ithprod_ct

gases during the energy release, the host species _ust also serve a_ the working fluid for a free radical or metastable propellant. Candidates for

the dual role of matriz host and workln_ fluid are _2' N2' 02' _e, Ne and Ar. A decisive advantage accrues if the free radical or metastable can be

produced in situ fron one of the latter matrix host species. Anong the

propellant candidates with this property, ator_ichydrogen in an H2 matrix is most accessible to near-term development with ex_stin_ technology.

Two main supplementary tech _icalaldo are now being employed in expert- i # ments to achieve higher concentrations of reactive species with matrix- !

isolation, namely, the use of very low temperatures (in the rnnge O.l°K to ' i 1.5°K) produced by advanced cryogenic apparatus and the use of very strong [ magnetic fields (in the range 50 k@ to I00 kO) produced by superconducting ! L magnets. A significant improvement in the trappln_ effectiveness of a { matrix is expected at temperatures below 1.5°K, while very strong magnetic i__ fields can prevent radlcal-radlcal recombination reactions by effectln_

the parallel alignment of unpaired electron spins in free radicals. Slgnl-

ficant concentrations of'atomic hydrosen, apparently about 10Z molar, have been obtained in the matrlx-isolated condensate from a hydrogen slow dis-

charge cooled very rapldly to about 1.S°K in a magnetlc field of approxl- 1 mately 50 kG. Similar experiments in prcBres_w_th m_gnetlc flelds as

larg_ as 1OO l_ till clarify tb_ effectlvenen_ oF th_ r,et_odfor _tc--Ic

u uuumpp = n J 1974009383-036

t hydrogen propellant manufacture and storage. The u_e of a radioactive

_ray emitter isotope (trltlu_ under current experimental study p32 , as t a proposed alternative) may yield _-H 2 propellants (with Isp _ 7_0 see ! estimated In the case of p32) by secondary electron inpact dlssocl_t_ons i ! of R2 in an impregnated matrix maintained below l°K (prospectively at

0.1°K in the case of trlti_n) In a strong maRnetlc field. Another nethod I for manufacturlng an H-ll2 propellant (_15% atomic hydrogen by weight, i

Isp_ 740 sec) involves bombardment of H2 with a cyclotron-produced beam of 10 HeV hydrogen atcms. I

Estimates of the characterlst_c t1_es for generic free radical reeom- i blnatlon reactions and generic r_etastable quenching reactions show that the matrlx-isolated reactive species must be used dlrect]y w_thout prior melting as solid propellants. Under suitab]e conditions, the deflagratlon of a free radical or metastable propellant Is expected to be steady and stable, albeit very rapid. A burning velocity of about 2.1 m/see Is predicted for an H-H2 propellant (_ 15Z atomic hydrogen by w©tght) at a chamber pressure of 100 psla, The handling problems associated with such f i solid propellants are believed to be amenable to experlmental solutions. t

;

J 1974009383-037

AppendS:,A: TheoretJcal ,q?ecif_cInnulse ._ori_ula

Let Q denote the overall net energy release per unit mass of propellant and n denote the overall,efficiency of the rocket engh,e in conver- tln_ this energy releaseto kinetic energy of the gas at the exhaust plane of the nozzle. Assuming that the sensible entha]py of the cold propellants is negligible% conpared to Q, the speelfJc _r_pulseis given by

Isp - CA.1) i ! where g _ 980 cm/sec2 is the acceleration of gravity at sea level. The I i overall efficiency for enere_yconversion in (A.1) can be e_.pressedas

n = _Ideal nlosses (A.2) ! in which _Ideal = 1- (temperatureof gas at the exhaust plane of the nozzle)/(chmlber temperature of the gas) is the _dea] thermodynamic efficiency of the rocket engine, and the factor nlos,_es(.

I . _2 -]-I (A.3) ideal [1 + 2(_ - I)"I ?lex t according to the theory for Invlscld, Isentroplc, one-dlmenslonnl flow of i a perfect gas with _ denoting the effective constant ratio of spec_flc heats and _ deno_In_ the ideal Mach number of the _as at th_ pxhaust plane of the nozzle. With optimum design the practical efficiency factor qlosses in (A.2), assoclatcd with posslble reductions in the exhaust velo-- city end "ach nt_ber du_ to unrecoverable heet losses to the ch_nber and nozzle walls, real gas viscous flow effects, etc., can be brought to

_or example, the sensible enthalp!es of H2 and 0 2 st their normal botltn_ poln_s (_o_ _n,1_0°_, respectively) are both less than .03 kcal/g_ and hence negligible co_pared to their stoichionetric energy release Q = _.18 kcal/_.

J ! i mm,m M mm 1974009383-038

+ a value close to unity Fro:a Invlscld, isentroplc, one-dlrens_ona] flow theory we also obtain t_e re]atlon between the e:_pans_onar¢_ratio of the nozzle, denoted here by R, ang the ideal Nach number of the gas at the exhaust plane,

R = Hex-1 [2(_+i)-I + (_-I) (_41)-I Mex2".](;+1)/2(T-l), (A.4) ' which can be inverted for R>>] to yield

l p _+I_(_+11/R,(-I2 (_+i_ o(R-(_-I)). [email protected] = ( __/ - _,_--y/+ (A.S) i ,, Thus, for a spacecraft with an expansion area ratio R = 60 and e.:haust

t gas with an effective constant ratio of specific heats _= I.?5, we find that (A.5) and (A.3) yield .Mex_ = 24.0 and nldenI _ .750, while for

R = 60 and _= 1.30 (A.5) and (A.3) vle]d _2 = 27.9 and _Ideal " .808 respectively. If we assume the latter values for R a_,d_ aad set the efficiency factor Ulosses equal to unity in (A.2), we obtain the theoretlcal specific impulse formula from (A.X) and (A.2),

fProvl.de_that thermodynamic equilibrium is maintained between the molecular I r (interr.aland translatlonal) degrees of frnedom durln_ the expansion of the

_as through the nozzle, energy partltlon_d into the vibrational, rotational ii

and electronic excltatlons 18 taken into account in the value for _. Since '_ I decreQses toward unity as the nunber of effective internal de_rees of

freedom increases, the ideal thermodynamic efficiency is reduced by an

increase in the number of internal de_rees of freedom accord_n_, to (A.3) and

(A.5) _Ith R fixed. On the other hand_ ene r_7 losses due to nonequillbrlu_

ftnite-.ttme rel_xat£on of the internal degrees of freed_ must be taken

into account through the f_ctor n losses'

L m , qlm m I 1g74009383-O3g

"" I = 265 (Q/I kcallgm)_ sec, sp (A.6)

[for R = 60, $ = 1.30, nlosses = 1].

Formula (A.6) is used to estimate the performance of propellants In the

body of thle report. For example, in the case of the conventlonal chemi-

cal propellant hydrogen-oxygen system wlth the optimum mlxture ratio 4.7

of 02 to _2 by weight, we have Q = 2.95 kcal/_m and (A.6) gives Isp = 456

SeC.

Appendix B: Local Heat Pu]se Produced b_ a Chance Reaction of Free P_adlcalsIn a _atrix

Follovlng Jackson91, let N denote the energy transmitted tc the lattice

by the recombination reaction of a palr of free radicals. Since only a

fraction of the total energy release from such a recombination reaction will

be absorbed by the lattice, we have W < 4.5 eV for H + H-_H 2 and W < 9.8

@V for N 2. Let Tf denote the minimum local steady-state temperature N-_N

required for freeing a radical from a trapping site and TO denote the ini-

tial uniform temperature of the solid matrix. Then trapped radicals may

possibly be freed by the approxhMtely Ceussian heat pulse that ensnares

from a chance reaction through a spherical region of radius

rf,s[wluc (Tf - TO)]I/3 Is.l)

in which n a.O4$moles/em 3 A. the concentrltion of molecules (e.g.. R2 or

H2) in the solid and c6 [(Tf + To)/20°K]3cal/uole - OK 6 2.6 x 1019 [(Tf + TO)

/20°X]3eVlnole - °K is a simple approxiuatton for the mean solar specific heat

of the solid (proportional to T3 at temperatures below 8bout IS K) in term8 of

the mean tenperature J(T(+Te) over the thernsl tense of interest (see aef. 91). |

i i _ , mgl n _- I 1974009383-040

w • _

Letting D denote the thermal dlffuslvlty of the solid, it follo_,sthat

trapped radicals wlt_In _Jstance rf of the recomblnatlvn reaction experi- ence the heat pulse durlnF a time duration p,Iven approximately by

tf =_rf2/D-_ [_/nc(Tf - To)]2/3/D. (B.2)

For the typlcal parnmeter values N = 2 eV, Tf = I0°}:,D _ 150 c_2/sec at T _ 4°K and D --_100 cln2/secat T _ 1°_'.t,,eobtain O O

rf e .95 x 10-6c_ _- at T _ 4°K (B. 3) i0_i& J o tf _ .60 x s_c

1.05 x 10-6cm rf at TO _ l°K. (B.4) ) tf _ 1.10 x 10-14see

It is evident that radicals in the v!cinit7 of a chP.nce recor_binntion

reaction cannot absorb requisite energy and escape their trappinF sites

during the small ch_racteristic time of order 10-14 sec in (B.3. _ and (B.4),

for a radical wouid have to acquire a velocity of the order 106 cm/sec to move

an AngstrOm during the characteristic time of the heat pulse. Hence, a quantum

mechanical treatment of the trapping stability problem is required.

Appendix C: _tanufacture of an H-}12 Solid Propellant by Ul_ra-Fnerp, etie H_ro_.en Atcen Bombardment

A eonveutlonsl cyclotron of 1950 vlnta_e, vith • wuqmet of I00 inch diameter and radiofrequency power supplied at about 250 kV, viii deliver

an ezternal (extracted) bern of IOMeV protons at a steady current of about

• .2 =U_dk 1.2 x 1017 protons/see (luplytng 8 bess pover of shout 192 1dO.

gush 8 beam of high energy proton8 can be nede to have s uniform flux over

a eroes-_ection81 ares of _out 3 x 1¢3 cm2 (by electric or us_netie field

dispersal focusing) and to pass from vaeuun through a chamber filled vtth

J J ' ! l _=,--_ m : I lilt 074000383-04

cesium vapor at a density of al,out 1017 c_,:;Itu_a:c: c/c._3. S_nce tl_e

" total cross-sect_on for the chargc--exchanye Froce_._ leading to a,,v neu-

tral (possibly electronlca]]y e:

lq + Ce+, can be estimated for 10 MeV proton_ by extl_,,.<_,etlonof ]o_Ter

energy data (SplesslT8) to be at least 10-16 cm 2 , Jt fo]]c_'s that almost

all of the protons _'III be converte'J to neutral hydrogen etov,r if the

cesium vapor neutra)Izln5 che-,ber hcs c. length along the bea_ of about

lO cm (see l_ughes86 for a detailed dlsct,s,_ion o[ tim technCque). In thJ_

manner it is possible to prc,duce a beam of 10 MeV hydrogen ato:_.qwi +:"a

uniform flux of about 4 x 1013 partleles/cr?-see over a eroE.s-sectlona_

area of about 3 x 103cr?.

Now suppose that a I0 liter volume (equivalently, .7] ken) of l lu_d

y.2 is cooled grad_-]ly thrc.u?h Its freezin_ point ,_nd do,,,,: to a re: peroturo

below 0.sOK to yield a wafer of solid t!2 clout 3 x ]03crl 2 in area _Jnd 2.7 c_.

in thickness. The wafer of solid H2, a rlfld lattice cor:po.-:cofd ebout 1026 2.14 x H 2 molecules, will have a nearly perfect crystalline str_cture,

good thermal conductivity, very low specific heat, end thus vet/ high thermal

dlffusivlty (Contrcras 36 j Miller 127) *

Let us consi'cr bombardment of the ultra-cold wafer of s_Itd H 2 by the

bun of I0 MeV hydrogen atoms d_scrlbed above, l_svlng a velocity of about

&.4 x 10 7 m/see, the l0 MeV hydrogen a_oms srlll enter the solid without the

significant backscatter and reflection observed experimentally at _uch lower I

bombardment energies (Brac_ann 16, Ylte $I). This is because at the hIF, h

velocltles of a_or_ in the beam the cross-sections for _-H 2 scatterln_ and

reaction processes are very roll (i.e., weli below the 8eomatrleal 4 z l0 "16

cm2) and scattering mnpli_udes are sharply peaked in the forward dlrae_.Ion.

Because the H2 molecules in the aoli4 lattice are separated by a distance (about 3_) which is rout, ely three tines the diameter of an E2 molect-le, a 1 1974009383-042

I0 HeV hydrogen atom t will travel about 2.0 cm in the solid H2 before beinF brought to rest by energy-absorbing processes. Most of the energy of the i0 MeV atoms will be absorbed by ionization reactions which ta_e on the average 38 eV per ion-electron pair and yield energetic free electrons Z that move preferentially in the direction of the hydrogen atom beam. There will also be knock-on dissociation reactions }I+ H2--_3}! by the primary

L'ydrogen atoms, yielding secondary energetic chain-branching hydrogen atoms which also move preferentially in the direction of the original 5ea-_.

The secondary energetic free electrons and hydrogcn atoms will also give up tPeir energy primarily through _onization reactions and H 2 dissociation reactions #%. In the course of these reactions, the excitatlou of l_ttice vibrations (associated with the sensiLl_ heat content and temperature of the solid) will not be favored quant_n mechanically if the temperature is maintained below l°K during bombardment. This is because the higher frequency vlbratlonal modes (chat couple to localized energetic interactions) are frozen out of the equilibrium distlibutlon by quantum statistics at low temperatures, and hence the rates at wh|ch the higher frequency vibrational modes can be excited are very small in a lattice below l°K by detailed I | balancing considerations.

' atom initially with I0 MeV energy will lose its electron end ¬hydrogen travel as a proton during about half the time it spends in motion in solid hydrogen; it is understood tacitly in our discussion that "hydrogen atom" means "hydrogen atom or proton" i

#%The dlssoclatlon energy of a ground-state H2 molecule is about 4.5 eV, but electrons having at least 11 eV are required for the quantum mechanical threshold of the dissociation reaction e + R2--b-e + 2H, which involves a transition of the molecule from the 1E 8round-state to a 3Z repulsive state. Near threshold, each free H emerges with about 3.2 eV of translational ktn¢- i tic energy. 1974009383-043

It Is estimated that less than .03% of thc total beam po_,arwill eventually be absorbed by lattice vlbrations_. On the other hand, the vibrational excitation of H2 moleculea (by impact with prlnary and secondary hydrogen i atoms and free electrons) will absorb a more significant fraction of the ! total beam power, but the vibrational excitation of an H2 _oleculc in the lattice will Increase the probabillty and lower the energy _equir_ent t for the chaln-branchlng dissociation reactions e + H2-_-e + 2N and i"

H 3H (see Truhlar194). It Is estlmnted that between 25% and 50% , H2-_ tq" ' of the orlginal energy in the beam will be absorbed eventually by chain- branching dissociations of H2 molecules, which generate additional fast- moving free hydrogen atoms as well as residual free hydrogen atoms. The ;_ latter free IIatoms may become trapped Inter_tltlally (Bondybev12) or t assume lattice sites occupied previously by H2 molecules which have been dissociated. If we take .375 as a tentative estimate of the energy fret- _ 4 tton finally absorbed by chain-branchtn_ dissociation reacttons j it fol- :_ lows that a hydrogen atom with an initial energy of 10 NeV will insttsate i the eventual production of about 1.66 million free hydrogen atoms in the i solid. Conditions will be favorable for the trapplns and stabilization of the free hydrosan atoms if a m_nette field of about 100 kG is applied through the solid, i

m_L/sec throuBh the entire volume. 81vin8 a loesl heating rate of about 1.8 *":"*; ii_ XlO'{Jeal/ea3-eee) 48 controllable by virtue of the very high thermal difftm£- :,.. vity of solid h_)'drosen,of the order lO|en_./see fo_ temper_ttmm below 1°i_. _ :i , tttiebruS_ mustnoteveabntuallu_.rbedy bybethe_tttaddtuoelataslonvis£bleof andRl UOIeultra_viLloleU t endrad£a_ttleet£on, vibra- ' ' '."_""_ t reset/J4 from eleetron£e ree_bL_aeton oJ_lens sad I_herlui:iLat£ve dse.sy of :;/:;:_,::_:i v£bratlonally tme/ted .... mlaaolu ,mst¢ou tea:tlv emlt. u l ii"...... 1974009383-044

In this manner about 2.0 x 1023 free hydrogen atoms will be produced

and trapped in the solid during each second of bombar_ent. F.ence, about

15Z of the I_2 molecules in the solid will v !ergo effective dissociation

to yield trapped free hydrogen atoms during a total bombardment ti_e of

about S.5 minutes. The resulting H-H2 solid propellant _afer, 15_ free

hydrogen atoms by _ei_ht, will have a stored recoverable specific energy

Q _ 7.81 kcal/gm and thus will yield a theoretical specific impulse

lap,_ 742 sac for rocket engine conditions that make formula (A.6) applicable.

It should be noted that the overall efficiency for energy storage in

the H-H2 solid propellant is approxi_nately .28, with 250 k_T cyclotron

power for 5.5 minutes yielding 5.55 x 103 kcal of stored energy in a .71 k_ wafer o._ solid hydrogen. To produce a 1000 k_n amount of the propellant would require a conveyer belt operation and 129 hours of total bombardment

time. The strong magnetic field must be maintained, along with the low

temperature, for safe storage of the propellant, and the atomic hydrogen

concentration can be monitored conveniently with electron spin resonance measure_ents during and after the bombardment of a wager.

Appendix D: Hanufacture of an H-H_ Solid Propellant by I_apre_n_a.tion _rlth _adioactive Phosphorus

The radioactive isotope of phosphorus p32 decays solely by _-ray

electron emission (to yield sulfur S32) vith a half-life of 14.3 days and

a Bean energy of 690 keV for the emitted _-ray electrons. About 300 ti_es

8ranter in specific activity than trAtium, the radionuclide p32 has been

axtensively used in medical applications and is available c_ercially. 1 1974009383-045

Consider a volume of liquid hydrogen impregnated uniformly with radio-

p3_ active phosphorus atoms in the ratio of one atom for every 50,000 _2 molecules (i.e., .002% molar p32) and cooled gradually through its freez- ! ing point and down to a temperature below l°K, which is maintained for a two-week "curing" period. During thls ti_e about half of the p32 atoms I wlll emit S-ray electrons having a mean energy of 690 keV and a mean range I in the low-denslty solid of about 2 cm. Almost all the energy of the

_ray electrons wlll be absorbed by ionization processes which yield secondary electrons with energies between 15 eV and 10 keY. The secondary electrons will in turn give up their ener&y through further ionization reactions, vibrational and electronic excitations of H2 molecules, dis- I i eoclations of H2 molecules, electronic excitations of H atoms, and lattice (collective molecular) vibrational excitation reactions. At least a tenth of the original energy In the S-ray electrons will be effective in producing free hydrogen aton_ via secondary electron impact dlssocla- r tion reactions and free hydrogen H + H2--_3H dissociation reactions. Since the net energy absorbed per dissociation is 4.5 eV, at least 1.53 x ]0 4 H2 t molecules will be dissociated by the secondary energetic particles that i are generated by a _-ray electron with 690 keY initial energy. Thus, durtn_ i i the two-week curing period, at leas£ 15Z of the H2 molecules viii have under- ! sons dissociations to yield free hydrogen atoms. If a masnetic field of J about 100kG Is applied to the solid, cendttions will be favorable for the trapping and stabilization of the free hydrogen atoms in the H2 matrix.

The resulting H - H2 solid propellant, at least ISX atomic hydrogen by velght, viii yield a specific impulse _ 742 see for rocket enslne conditions that make formula (A.6) applicable. \ 1974009383-046

Appendix E: Defla_ration of an H - H_ Solid Propellant

Consider an E - H2 solid propellant, 15% atomic hydrogen by weight, at an initial temperature of i°K and a constant pressure of i00 psia. If an elemental volume of the solid is heated, the density will remain appro- xlmately constant at Ps " .088 gm/cm3 until the melting point is reached i at a temperautre Just above 14°K. The density of the fluid, equal to about i I .073 gm/cm3 at a pressure of I00 psia and a temperature near the melting t point, will decrease continuously with increasing temperature according to I the formula I 0_ (.170 Em-°K/cm 3) (T --ii.67°K)-I (E.l) , for T > 14.0°K without slgnlflcant discontinuity at the llquld-_as transl- tlon temperature-.32°Kat I00 psla (because the critical point for H2 is at 33°K and 189 psla). Continuity of mass flux in the case of steady one- p dimensional deflaEration yields the relation

pu- Ps where u i8 the local fluid velocity in a coordinate frame for which the t malting surface is at rest and Ys Is the constant burning velocity of the solid (i.e., the rats of linear regression of the melting surface with re- spect to the solid at rest). It follows from (E.l) and (F.2) that

u .L. 518 "¢s (_' -- 11°6 ,) (E. 3) for a fluid element at temperature T.

New with the propellant ntxt_re yteldin8 the overall net enerSy release

Q _, 7.81 kcal/_, the functional dependence Cp_ e_(T) for H2 gives a final

(¢diabattc flame) temperature Of about 2090°K for the product H2 gas. If

I Lt 1974009383-047

! 45 i

At denotes the time interval following melting for a fluid element to

attain the temperature of 1000°K, then the temperature of a fluid element wlll increase by the amount AT = 1000°K--14°K - 986°K in travelllng the

Ax _ u dt (E.4) distance A_ I O

from the melting surface. Lettlng m denote the weight fraction of H atoms at any point in the fluid, we have the recombination rate equation

d__ dt . _ f2 5)

In whlch

f - 1.61 x I011__p)(_I__K)'_ sec -I (E.6)

18 the rate function assoclatedwith a veloclty-averaged total cross-

r section of _i.I x I0 -16 cm2 for the reco_blnatlon reaction. The temperature of a fluid element will increase from Ttl4°K (for which w z_ .15. see below) to T_2090°E ( for which w = o) with an approximately i" linear t dependence on w, ! 4

T-L2090°K "- (13,840°K)w • (E.7)

By putting (Z.3) and dt - f-ld(_'l) into (E.4) and using (R.6), (E.1) and (Z.7), ve obtain

_Thseffective specific heat of the tl.id te bolstered at low teuperatures by the heat of vaporization (.-107 eal/am) distributed about 32°K and by

the heat of conversion of para_H 2 to ortho--H 2 (_170 cal/sm converted).

...... w "=_ ...... 1974009:38:3-048

tO¢O + e - 11.67 dO Az g= (8.65 (E.8) x 10-8 sec) v a 2"0_0 - e e½

_- (7.0 x 10-7 sec) v s •

Thus, the thermal gradient for heat flux to the meltlng surface is given

approximately by

AT (;.#1X 109 °K/sec)Vs-I (E.9) I

The latter quantity enters the heat flux balance at the melting surface, i l

AT I _ _-v s Os hi, (E.IO) !

t where A _ .25 mW/cm°-K-"6.0 x i0-5 cal/cm-sec-°K is the estimatedt thermal i

te- l conductivity of the fluid at 14°K and ht _ 22 cal/gtais the enthalpy | 2 qulred to warm and melt a unit mass of the solid initially at l°K#T." t Hence, from (E.9) and (E.10) we obtain the burning velocity ! i _t " 210 cm/sec. (E.II) S

The essential correctness of the deflagration model is confirmed by i_.

consistency estinates. First note that an elemental volume of the solid " _tI viii be warmed to the melting point in a time 8ivan approximately by the _i ii

%A significant fraction of ortho-Ho will be present in the solid as a by- i+ product of the propellant menufact_rinf_ process, and the ortho-H, and ato_i_ + H fractions will supprea 8 the thermal conductivity from the valu_ ._'SmW/_m-"K +_ for liquid para-_ 2 at 14 E and 100 psia. j

+ *%Wahave 14 eal/_n courtn_ from the heat of fusion. 5 cal/p frou the T$ tnte- i 1s.ta6 tion,K (withand aabhighout f3ractcalio/gmn offroorm ththeo-R,A azno_umltalyiminK heatin thecapsaocilitdy aeat a abyb_tproduct _' of the propellant manufacturing proces|). 1974009383-049

expression D/vB2__-- 8.0 x 10-9 sec, where D _ 3.5 x 10-4 cm2/sec

is the thermal dlffuslvlty of the solid at a temperature near the melt-

Lng point, and thus a negligible fraction of the hydrogen atoms will have

time to recombine while in the solid and above the critical tenperature

(_d°K) for significant escape from trapplnz sites. Next observe that

the distance Ax ---1.47x 10"dcm [given by (E.8) and (E.II)] has the s_e

order of magnitude as the mean free path for R2 molecules at 1000°K and

100 pala. On the other hand, the magnitude of Ax is small compared to

the entire flame thickness, which can be estimated to be about 1.81 x 10-2

an by replacing the upper limit in the integral in (E.8) with the value

2000. Finally note that the neglect of species and thermnl diffusive t transport in writing Eqs. (E.5) and (E.7) is Justified, because the dlf-

fuslvltles in the fluld are v&ry small compared to the mean flow velocity

I _I.07 x 105 cm/sec multiplied by the approximate flame thick- T.IOOOOK t nes8 1.81 x 10-2 cm.

• i

I I .

I 1974009383-050

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45Drake, G. W. F., and Dalgarno, A., "2p2 3p and 2p 3p Ip States of the

Helium l_oelectronic Sequence", _Phys. Rev. A, Vol. i, 1970, pp.

1325-1329.

46Dupont-Roc, J., et el., "New Value for the Metastability Exchange Cross

Section in Helium", Phys. Rev. Left., Vol. 27, 1971, pp. 467-470.

47Easley, W. C., and Weltner, W., Jr., "ESR of the CN Radical in Inert i

Matrices", J. Chem. Phys., Vol. 52, 1970. pp. 197-205.

4SEtters, R. D., "Binding Energies for Clusters of Atomic-Triplet

Hydrogen 'e, Phys. Left., Vol. 42A, 1973, pp. 439-441.

49Evans, S. A., et el., "Quantum-Mechanlcal Calculation of Cross Sections

for Inelastic Atom-Atom Collisions. I. Inelastic 23S _23p Collisions

between Metastable and Ground-State Helium /,toms", Phys. Rev. A, Vol. 4,

1971, pp. 2235-2240.

50Feinberg, G. and Sucher, J., "Calculation of the Decay Rate for 23SI_ llSo

+ One Photon in Helium", Phys. Rev. Lett., Vol. 26, 197], pp. 681-684.

51Fire, W. L., and Guthrie, G. L., "Formation of Free-Radlcal Solids Using l

Atomic-Beam Techniques", AFOSR-TN-59-364 (1959).

$2Fite, W. L., et sl., '_ifetime of the 2S State of Atomic Hydrogen", I Phys. Rev., Vol. 116, 1959, pp. 363-367.

$3Fite, W. L., et el., "Ionization and Charge Transfer in Proton-Hydrogen • i

Atom Collisions", ?hYS" Rev., Vol. 119, 1960, pp. 663-668. { ! 54Flournoy, J. M., "Studies of Excited Hydrosen in Relation to Advanced I i

Propulsion", AFOSR-TR-72-0504 (1972). i

$$Flournoy, a. M., and Nelson, L. Y., 'Wibrational Excitation of HCN",

Chem. ?hrs. Lett., Vol. 6, 1970, pp. $21-$24.

_Fontena, B. 3., "Thermometric Study of the Frozen Products from the

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Hicrovave Discharse", 3. '.C_m.. lqws,, ¥o1. 31, 1959, pp. 148-153. 1974009383-055

i 58Fowler , W. B., and Dexter, D. L., "Electronic Bubble States in Liquid I

Helium", Phys. Rev., Vol. 176, 1968, pp. 3]7-343.

59Freed, K. F , and Jortner, J , "Radiative Decay of Polyatomi_ Molecules"

J. Chem. phys., Vol. 50, 1969, pp. 2916-2927.

60Freis, R. P., and Hiskes, J. R., "Radiative Lifetimes for the 2pT_3_][ u

State of the Hydrogen Molecule", Phys• Rev. A, Vol. 2, 1970, pp. 573-

580•

61Freund, R. S., '_olecular-Beam Measure_ _nts of the Emission Spectrur_ and

Radiative Lifetime of N2 in the Metastable E3-+_-State",g J. Chem. Phys. VOI. 50, 1969, pp. 3734-3740.

62Freund, R. S., "Electron-Impact Excitation Functions for Metastable States

of N2" , J. Chem. Phyj., Vol. 51, 1969, pp. 1979-1982.

63Freund, R. S., et al., "Radio-Frequency Spectrum of Metastable N2(A _u ). I. I ; Magnetic HyperfJne and Electric Quadrupole Constants", J. Chem• Phys., I I Vol. 53, 1970, pp. 2290-2303. i 64Freund, R. S., "Radiative Lifetime of N2(a I_[Ig) and the Format.ion of [_ Metastable T N2(a'l_[u)", J. Chem. Phys., Vol. 56, 1972, pp. 4344-43_Cl.

65Garstang, R. H., 'Theoretical and Experimental Forbidden Atomic Transition

Probabilities", Mere. Soc. Roy. Sci. Liege, Self. V, Vol. 17, [969,

pp. 35-46.

66Garstang, R. H., '_Forbidden Transitions" in Atomic and Molecular Processes, f !

ed. D. R. Bates (Academic Pres_, New _ork, 1962) pp. 1-46. jl

67Gersh, M. E., and Muschlltz, E. E., Jr., '_eloclty Dependence of the !ii ! Cross Section for the Ouenchzng of 3p Argon in Collisions with 0,2 ;4olecular Oxygen", .Bull. A.P.S., Vol. Ig, 1973, p. 809.

68Gersh,-- M. E., and Musehlltz, E. Z., Jr., '_eloc/ty Dependence of 3pn2_, Argon in Coll_.stons v/Oh K_lecular Oxygen" (preprint of pa_er presented

at the Tventy-flfth Annual Gaseous Electronics Conferev._e, London,

Ontario, Canada, Oct. 17-20, 1972).

-- • II II ...... 1974009383-056

69Goddard, W. A., III, et al., "Group Theoretical Selection Rules for

Electron-Impact Spectroscopy", Chem. Phys. Lett., Vol. II, 1971,

pp. 329-333.

70Golden, S., "Free-Radical Stabilization in Condensed Phases", J. Chem. tI Phys., Vol. 29, 1958, pp. 61-71. I

71Guberman, S. L., and Goddard, W. A., "On the Origin of Energy Barriers I !

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72Guillory, W. A., and Hunter, C. E., "Infrared Spectrum of Matrix-lsolated

(NO)2" , J. Chem. Phys., Vol. 50, 1969, pp. 3516-3523.

73Guillory, W. A., and Smith, G. R., "Far-Infrared Fourier Transform

Spectroscopy of Matrix-Isolated Species", (preprint of paper to

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75Hansen, J. P., and Pollock, E. L., "Liquid-Helium Configuration around a I.,i Metastable Excited Helium Atom", Phys.. Rev. A, Vol. 5, 1972, pp. 2214- { 2216 761tetdner, R. F.,. III, and Kasper, J. V. V., "Observation of Vibrationally

Excited H2 in Active Hydrogen", J. Chem. Phys., Vol. 51, 1969, pp. 416_- 4164

77Hennek er' W. H., and Popkle, H. E., "Theoretical Electronic Transition

Probabilities in Diatomic Molecules. I. Hydrides", J. Chem. Phys.,

Vol. 54, 1971, pp. 1763-1778. t 78Here£ord ' F.L., ,,Diffusion-Limited Destruction of Hetastable States in

He II", Phys. Ray. Lett., Vol. 29, 1972, pp. 1722°1725. \ 79Herr, K. C., et al., "Investigations of Free Radical Reactions with Rapid- \

Scan Ingrared Spectroscopy: Flash Noise as a Limiting Factor", Kagaku

_, Vol. 21, 1967, pp. 11-20.

_t b 1974009383-057

80Hess, R., "Studies on the Stabilization of Atomic Hydrogen by Means

of Low Temperatures and Strong Magnetic Fields", NASA TT F-14, 123 J

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81HIll, J. C., et al., "Evidence of Metastable Atomic and Molecular Bubble i

States in Electron-Bombarded Superfluid Liquid Helium", Phys. Rey.

Lett______.,Vol. 26, 1971, pp. 1213-1216. !

82Hiskes, J. R., "Excited Atomic and Molecular Systems for Neutral Injection i I into Plasmas", Bull. A.P.S., Vol. 17, 1972, p. 1144. !

83Holland, R. F., "Excitation of Nitrogen by Electrons: The Lyman-Birge- I L Hopfield System of N2", J.. Chem. Phys., Vol. 51, 1969, pp. 3940-3950. ! 84Holt, H. K., and Sellin, I. A., "Time-Dependent Theory of Stark Quenching

of 2S States in Hydrogen and Helium", Phys. Rev. A, Vol. 6, 1972, pp. ! 508-512.

85Howard, J. S., et al., "Chemi-iontzation in Collisions between Helium t Metastable Atoms and Argon", Phys. Rev. Lett., Vol. 29, 1972, pp.

it 321-324.

86Hughes, R. H., and Choe, S.-S., "Excitation to the 2s State of Hydrogen

by 20- to 120-keV Hydrogen-Atom Impact on He, Ne, At, and N2", Phys. t

Rev._.____A19, 72, pp. 1758-1753. _

871ce, G., and Olson, R., "Semlemplrical Calcc! clons of He* + Ar loniza- |!!

tion Total Cross Sections", Bull. A.P.S., Vol. 17, 1972, p. 1132.

881nterrante, C. O., "Interpretive Report on Effect of Hydrogen in

Pressure-Vessel Steels: Basic and Research Aspects", Welding Res.

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89jackson, J. L., "Free Radical Trapping- Theoretical Aspects" in

Formation and T.rapping o.f F:ee Radicals, ed. A. M. Bass and H. P. \

Broida (Academic Press, New York, 1960) pp. 327-346. 1

90jackson, J. L., and Montro11, E. W., '_ree Radical Statistics", J.__. _ .

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91jackson, J. L., "Dynamic Stability of Frozen Radicals. I. Description

and Application of the Model", J. Chem. Phys., Vol. 31, 1959, pp.

154-157.

92jacobs, V., "Two-Photon Decay Rate of the 2iSo Metastable State of

Helium", Phys. Rev. A, Vol. 4, 1971, pp. 939-944.

93jacox, M. E., and Milligan, D. E., "Spectrum and Structure of the HO 2

Free Radical", J. Mole. Spectroscopy, Vol. 42, 1972, pp. 495-513.

94jacox, M. E., and Milligan, D. E., "Infrared Spectrum and Structure of

the Species C03" , J. Chem. Phys., Vol. 54, 1971, pp. 919-926.

95jacox, M. E., and Milllgan, D. E., '_atrix-lsolacion Study of the f Vacuum-Ultraviolet Photolysis of Methyl Fluoride. The Infrared

Spectra of the Free Radicals CF, HCF, and H2CF" , J. Chem. Phys.,

Vol. 50, 1969, pp. 3252-3262. t

96jacox, M. E., and Milligan, D. E., 'IMatrix-lsolation Study of the !

Infrared Spectrum of the Free Radical F2CN" , J. Chem. Phys.,

Vol. 48, 1968, pp. 4040-4046. r

97james, T. C., "Transition Moments,Franck-Condon Factors, and Lifetimes 1 of Forbidden Transitions. Calculation of the Intensity of the i

Cameron System of CO", J. Chem. Phys., Vol. 55, 1971, pp. 4118- _

4124.

98johnson, A. W., and Gerardo, J. B., "Ionizing Collisions of Two Meta-

stable Atoms (23S) '', Phys. Rev. A, Vol. 7, 1973, pp. 925-928.

99johnson, C. E., "Quenching of the 2°S o Metastable State of Helium by

an Electric Field", Phys. Rev. A, Vol. 7, 1973, pp. 872-880. lOOjohnson, C. E., "L_fetime of the _31_ u Metastable State of H2, D2, and

HI)", Phys. Rev. A, Vol. 5, 1972, pp. 1026-1030. lO1johnson, C. E., 'q, ifeCtme of the 2p33|5S Metastable State of Oxysen", !

Phys. ReX. A, Vol. 5, 1972, pp. 2688-2689. _ ! 1974009383-059

102johnson, C. E., private com_unication dated June 4, 1973.

103johnson, S. E., '_easured Radiative Lifetimes and Electronic Quenching

Cross Sections of Ba0(AI_-)'',J. Chem. Phys., Vol. 56, 1972, pp. 149-

154.

104jones, J. T., Jr., et al., "Characterizations of Hydrogen Atom Systems",

Aeronutronic Systems, Inc., Publication No. U-216 (1958).

105Kass, R. S., and Williams, W. L., "Quenching of Metastable Hydrogen by

Helium", Phys. Rev. Lett., Vol. 27, 1971, pp. 473-474.

106Kauppila, W. E., et al., "Excitation of Atomic Hydrogen to the Meta-

stable 22S_ State by Electron Impact", Phys. Rev. A, Vol. I, 1970, pp. 1099-1108.

107Kepford, C. R., et al., "Experimental and Theoretical Investigation of

Energetic Compounds for Advanced Chemical Propulsion", AFRPL-TR-69-24

(1969).

108Keto, J. W., et al., "Dynamics of Atomic and Molecular Metastable States

Produced in Electron-Bombarded Superfluid Helium", Phys. Rev. Lett.,

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IO9Kiefer, J. H., and Lutz, R. W., "Vibrational Relaxation of Hydrogen",

J. Chem. Phys., Vol. 44, 1966, pp. 668-675. llOKim, Y.-K., and Inokuti, M., "Generalized Oscillator Strengths of the

Helium Atom. II. Transitions from the Metastable States", Phy9. Key.,

Vol. 181, 1969, pp. 205-214. lllKlarsfeld, S., "Interaction of Metastable Hydrogenlike Atoms with

Electromagnetic Radiation", Phys. Rev. A, Vol. 6, 1972, pp. 506-508. ll2Kolker, H. J., and Michels, H. H., "Elastic Scattering, Diffusion, and

Excitation Transfer of Metastable Hellum in Helium", J.:.Chem. PhyS.,

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iI 1974009383-060

58 llAKrotkov, R. V., eta]., "Collisional Quenching of Metastable Hydrogen

Atoms", Phys. ReD. A, Vol. 5, 1972, pp. 2078-2084. llSLawton, S. A., and Pichanick, F. M., "Resonances in the Total Cross- | Section for Electron Excitation of Metastable Molecular Hydrogen", I !

_Phys. ReD. A, Vol. 7, 1973, pp. 1004-1011. i ll6Lefebvre-Brion, H., and Guerin, F., "Calcula _;_,nof the Radiative i

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pp. 1446-1447. ll7Lichten, W., "Quantum Mechanics of a Double Perturbation: Application

to the Zeeman Effect of Metastable HydroBen Molecules", Phys. ReD. A,

Vol. 3, 1971, pp. 594-603. ll8Linevsky, M. J., "Trapping and Spectroscopic Study of Metastable

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Phys. Today, Vol. 26, 1973, pp. 17-20.

120Hacek, J., "Theory of Atomic Lifetime Measurements", Phys. ReD. A, Vol. I, P

1970, pp. 618-627.

12_ansbach, P., and Keck, J., '_onte Carlo Trajectory Calculations of i Atomic Excitation and Ionization by Thermal Electrons", Phys. RED., i Vol. 181, 1969, pp. 275-289. t

122Harrus , R., and Schmleder, R. W., "Forbidden Decays of liydrogenllke and [

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123McNeal, R. J., et al. ' 'Quenching of Vltrrationally-Excited N2 by Atomic i OxYSen" , Bull. A.P.S., Vol. 18, 1973, p. 809.

12_Mede£ros, J. A., et al., '_[etastable Hydrogen Atom Quenching Co11/sions",

B.ull. A.P.S., Vol. 18,.1973, p. 808. 125.eyer, B., Low Temperature Sl)ectrosco_¥ (Amer. Elsevier Pub. Co., New York, 't 1971). 1974009383-061

126Mickish, R. A., and St. John, R. M., "Electron Excitation of H and

H2" , Bull. A.P.S., Vol. 18, 1973, p. 814.

127Miller, M. D., and Woo, C.-W., "Low-Temperature Specific Heats of

Adsorbed Helium Monolayers in the Mobile Limit", Phys. Rev. A,

Vol. 7, 1973, pp. 1322-1328.

128Miller, P. A., et al., "Behavior of He(23S) Metastable Atoms in I

Weakly Ionized Helium Plasmas", Phys. Rev. A, Vol. 4, 1971, pp. 692- i

700. 9M 12 iller, W. H., et al., '_olecular Autoionization Lifetimes and Cross i Sections for Penning Ionization: Numerical Results for He*(i$25 3S)

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130Milligan , D. E., et al., "Infrared Spectrum of the Free Radical NCN",

J. Chem. Phys., Vol. 43, 1965, pp. 756-757.

13_illigan, D. E., et al., '_atrix Isolation Study of the Photolysis of

Cyanogen Azide. The Infrared and Ultraviolet Spectra of the Free

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132Milllgan, D. E., and Jacox, M. E., '_atrlx-lsolatlon Study of the Photo-

lysls of Cyanogen Azlde. II. The Symmetric Stretching Fundamental of

the Free Radical NCN", J. Chem. Phys., Vol. 45, 1966, pp. 1387-1391.

13 3.illlgan, D. E., et al., "Infrared Spectrum of the NO ;Ion Isolated _i

in an Argon Matrix", J. Chem. Phys., Vol. 52, 1970, pp. 3864-3868,

134Mllligan, D. E., and Jacox, M. E., '_atrlx Spectra" in Molecular i

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135Milligan, V. g., and Jacox, M. g., "Infrared and Ultraviolet Spectro-

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in a Matrix Environment", Adv. Hish Temp, Chem., Vol. 4, 1971, pp. 1-42. \ 1974009383-062

. 136Milligan, D. E., and Jacox, M. E., "Infrared Spectrum and Structure

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Vol. 54, 1971, pp. 927-942.

137Milligan, D. E., and Jacox, M. E., "Spectra of Radicals" in Physical

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York, 1970)pp. 193-231.

138Milligan, D. E., and Jacox, M. E., '_atrix-lsolation Study of the

Infrared and Ultraviolet Spectra of the Free Radical HCO. The

Hydrocarbon Flame Bands", J. Chem. Phys., Vol. 51, 1969, pp. 277-

288.

139Mizushima, M., '_S= + 1 Magnetic Multipole Radiative Transitions",

Phys. Rev., Vol. 134, 1964, pp. A883-A888.

140Moos, H. W., and Woodworth, J. R., "Observation of the Forbidden 23SI--_

|#S o Spontaneous Emission Line from Helium and Measurement of the

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141More, R. M., "Theory of Decay States", Phys. Rev. A, Vol. 4, 1971, ! _ pp, 1782-1790. ! 14_oseley,. J. T., et al., "Deexcitation of Fast He, Ne, and Ar Metastable I

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143Mowat, J. R., et al., '_ean Life of the Metastable 23P1 State of the i _ I Two-Electron Fluorine Ion" (preprint of paper scheduled to appear in |

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14_uschl£tz, E. E., Jr., "Collisions of Electronically E'.:cited Atoms Ji

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146Nelson, L ¥ _ and Pimentel, O. C., "Infrared Detection of the Trlchloride

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4 1974009383063

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147Nesbet, R. K., '_olecular Orbital Theory and tile Physical Properties of

Molecules", J. Chem. Phys,, Vol. 43, 1965, pp• $30-$33.

148Neynaber, R. H., etal., "Hell+ Formation from Low-Energy Collisions of

Metastable Helium and Molecular Hydrogen", Bull. A.P.S., Vol. 18,

1973, p. 809.

149Nitzan, A., and Jortner, J., "Preparation of Metastable Molecular States

by Optical Excitation", Chem. Phys. LeSt., Vol. i4, 1972, pp. 177-183.

150Noble, P. N., and Pimentel, G. C., "Hydrogen Dichloride Ra4ical:

Infrared Detection through the Matrix Isolation Techniq U ei,, J. Chem.

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t 151Ogawa, T., etal., "Reaction Rate of Trifluoromethyl Radicals by Rapid

Scan Infrared Spectroscopy", J. Phys. Chem., Vol. 74, 1970, pp. 2090-

2095.

152paulson, J. F., "Chemical Evidence for a Metastable Excited State of C ",

J. Chem. Phys., Vol. 52, 1970, pp. 5491-5492.

153pearl, A. S., '_ifetime of the 21S State of He", Phys. Rev. Left., Vol.

24, 1970, pp. 703-705.

154penton, J. R., and Muschlltz, E. E., Jr., "Ionization of Hydrogen,

Hydrogen Deuteride, and Deuterium on Impact of Metastable Helium

Atoms", J. Chert. Phys., Vol. 49, 1968, pp. 5083-5088.

155petraaso ' R., and Ramsey, A. T., "Electric Field Quenching of Metastable i

21S ° Helium", Phys. RaY. A, Vol. 5, 1972, pp. 79-83.

156peCzinger, K. G., and Scalapino, D. J., "Pars- to Ortho-H 2 Conversion on

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- 158pimentel, G. C., "Infrared Detection of Reactive Species Produced

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LQ pp. 563-569. ._ 1974009383-064

159pimentel, G. C., "Rapid Advances in Rapid Scan Spectroscopy",

_, Vol. 7, 1968, pp. 2155-2160.

160pimentel, G. C., "Infrared Study of Transient Molecules in Chemice'l

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161pimentel, G. C., private cormnunication dated May 8, 1973.

162prior, M. H., and Shugart, H. A., "Radiative Lifetime of Metastable

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164Rogers, E. E., et al., '_atrix-lsolation Studies of the Infrared Spectra

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165Rosenfield, J., et al., "Possible New Type of Molecular Bound State",

J. Chem. Phys., Vo|. 53, 1970, pp. 1960-1969.

166Rosner, S. D., and Pipkin, F. M., "Temperature Dependence of the

Helium Metastability-Exchange Cross Section in the Range 15-I15°K '', t Phys. Rev. A, Vol. 5, 1972, pp. 1909-1918.

167Russek, A., et al., "Bounds on Energy Levels and Lifetimes of Auto-

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168Schmieder, R. W., "Double- and Trlple-Photon Decay of Metastable 3Po [i_

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1973.

169Schmieder, R. W., and Marrus, R., '_rvo-Phonon Decay and Lifetime of

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170Schnelderman, S. B., 'Theoretical Investigation of High-Energy Meta- \

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172Shaw, T. M., "Techniques of Electrical Discharge for Radical Production"

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173Sheridan, J. R., and Peterson, J. R., "De-excitation of Metastable

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174Simha, R., et el., "High-Speed Computation in the Kinetic_ of Free- i9 Radical Degradation, l. Random Initiation", J. Chem. Phys., Vol. 29,

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175Smialowski, M., Hydrogen in Steel (Pergamon Press, New York, 1962),

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176Smlth, C. E., et al., '_atrix-Isolation Study of the Vacuum-Ultraviolet

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177Smlth, J. N., Jr., an4 File, W. L., "Reflection and Dissociation of #

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178Spiess ' G., et al., "Absolute Detection and Colllsional Destruction of I 2.5-keV Metastable Hydrogen Atoms Produced by a Charge-Exchange

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_ 180Stebblng, R. F., et el., "Photolonlzatlon of Helium Metastable Atoms near i Threshold", Phys. Key. Lett., Vol. 30, 1973, pp. 815-817.

181Stedman, D. H., and Setse_, D. W., "Chemical Applications of Metastable

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J. Chem. Phys., Vol. 52, 1970, pp. 3957-3965.

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182Stedma n i • D. H., et al., "The Reaction Between Active Hydrogen and CI 2.

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183Steelhammer, J. C., and Llpsky, S., "Electron-Impact Excitation of the He

IIs,238, IIs-,23p, and IIs-,21 P Transitions", J. Chem. Phys., Vol. 53,

1970, pp. 4112-4114.

184Stockton• M., et al., "Ultraviolet Emission Spectrum of Electron-Bombarded

Superfluld Helium", Phys. Rev. Lett., Vol. 24, 1970, pp. 654-657. !

185Surk ° , C. M., et al., "Spectroscoplc Study of the Luminescence of Liquid

Helium in the Vacuum Ultraviolet", Phys. Rev. Lett., Vol. 24, 1970, i

pp. 657-659. h

186Takezawa, S., et al., "Selective Enhancement in Hydrogenllke Molecules with

the Rare Gases. I. H 2 wlth Ar and Kr", J. Chem- Ph_hy_S.,Vol. 45, 1966,

pp. 2000-2010. i

187Tan, L. Y., et al., "Infrared Spectrum of Gaseous Methyl Radlcal by Rapid i Scan Spectroscopy", J. Chem. Phys., Vol. 57, 1972, pp. 4028-4037.

188Tang, S. Y., et al., "Velocity Dependence of the Ionization of Ar, Kr, and t "Xe on Impact of Metastable Neon Atoms", J. Chem. Phys., Vol. 56, 1972,

pp. 566-572. i t

X89Thrush, B. A., "Radical Formation and Trapping from the Gas Phase" In [ ! 7ormation and Trapping of Free Radicals, ed. A. M. Bass and H. P. Brotda ; (Academic Press, New York, 1960) pp. 15-4.5. [ ! 190Tinti, V. S., and Robinson• G. W., "Spectroscopic Evidence for Slow t:i

Vlbrational and Zlectronlc Relaxation in Solids. The Vegard-Eaplan and

Second Positive Systeus of N2 in Solid PAre Gases", J. Chat. Phys.,

Vol. 49, 1968, pp. 3229-3245.

191TraJnmr, S., at el., '_ifferenttel sad Inteeral Croes Sections for the

• Electron-Impact Excitation of the sial aml b% + States of 02". i w

Phyp. by,. A , Vol. 4, 1971. pp. 1482-1492. _ .._._.... 1974009383-067

" " 65 :

192Trajmar, S., et al., "Angular Dependence of Electron Impact Excitation

T, Cross Sections of 02 , J. Chem. Phys., Vol. 56, 1972, pp. 3759-3765.

193TraJmar, S., "Differential and Integral Cross Sections for the Excitation ! of the 21S, 23S, avd 23p States of He by Electron Impact at 29.6 and

40.1 eV", Phys. Rev. Abstracts, Vol. 4, 1973, p. 6.

194Truhlar, D. G., and Kuppermann, A., "Exact and Approximate Quantum Mechanical

Reaetlon Probabilities and Rate Constants for the Coll!near H + _Z I

Reaction", J. Chem. Phys._ Vol. 56, 1972, pp. 2232-2252. I

195Truhlar, D. G., "Electron Scattering with and without Vibrational Excitation. I,

I, VIII. Comment on a Theory of Small-Energy-Transfer Collisions Dominated

by Long-Ranged Forces", preprint of paper to appear in Phys. Rev. A_ i t

July 1973. i

196Ultee, C. J., and Kepford, C., "Study of Stabil_zation of Hydrogen Atoms at i i 77°K and Higher Temperatdres", AFRPL-TR-68-73 (1968). i

197Van Dyck, R. S., Jr., et al., "Lifetime Lower LJmlts for the Metastable 3p i States of the Noble Gases", Bull. A.P.S.,Vol. 16, 1971, p. 533. i

198Van Dyck, R. S., Jr., et al., "Radiative L_fetime of the 21,e 0 Hetastable _.

State of Helium", Phys. Rev, A, Vol. 4, 1971, pp. 1327-1336. !.

199Van Dyck, R. S., Jr., et al., '_tfetime Lower Limits for the 3Po and 3P2. t:

Hetastable States of Neon, Arson, and Krypton", Phys. Rev. A, Vol. 5,

200Varetti, E. L., and Ptmentel, G. C., "Isomeric Forms of Dtnttroaen Trioxide

J. 1972in a, Npp.itroRen991-993.Hatrtx", Chemt Phys., Vol. 55, 1971, pp. 3813-3821. '! I' 201Varney, R. N., 'Matastahle Atoms and Molecules. I. Matastable States Produced

in Charge-Exchange Processes", Phys. ltev_, Vol. 157, 1967, pp. 113-115. i 202Wall, L. A., et al., "Zleetron. Spin BesoMnce Spectz8 from Gamu-lrradfated

Solid Nltro$en", J. Chem..Phys., Vol. 30, 1959, pp. 602-603.

*JB ...... ] 974009383-068

'_ 66

203Wells, W. C., et al., "Absolute Cross Sectlcn £or the Production of O(5E°)

by Electron Impact Dissociation of 02", Chem. Phys. Left., Vol. 12,

1971, pp. 288-290.

204Wells, W. C., et al., "Electror. Impact Excitation of Metastable States in

Carbon Monaxlde" (preprlnt of paper presented at Eighth Int. Conf. on

the Physics of Electronic and Atomic Colllslons, Beograd, Yugoslavl_

July 16-20, 1973).

205Weltner, W., Jr., "The Matrlx-Isolatlon Technique Applied to High Temperature

Molecules", Ady..High Temp. Chem., Vol. 2, 1969, pp. 85-105.

206Weltner, W., Jr., "Stellar and Other High-Temperature Molecules", Science,

Vol. 155, 1967, pp. 155-164.

207Whltson, M. E., Jr., et al., "Quenching of Vibratlonally-ExcltedN2 by N20", Bull. A. P. S., Vol. 18, 1973, p. 809.

208Wlese, W. L., et al., "Atomic Transition Probabilltles I, Hydrogen through

Neon", NSRDS-_S 4 (GovernmentPrinting Office, Washington, D. C.,1966 .

209Wi111amson, W., Jr., "Electron Excitation Cross Sections for Light Atoms

Using Slater Wavefunctlons", J. Chem. Phys., Vol. 53, 1970, pp. 1944-1948.

210Wlndsor, H. W., 'Trapped Radicals in Propu18Ion" in Formation and Trapping of

Free Radicals, ed. A. H. Base and H. P. Brolda (Academic Press, New York,

1960) pp. 387-409. ' i

211Wlndsor, H. W., "Studies of Trapped Radlcels st Liquid Helluu Temperatures",

Paper No. 73, Fifth lnternatlonal Syupoelum on Free Radlca18 (klmqulst and

MtkHll, Stockholm, Sweden, 1961).

212Wlndqor, _/. W., private eoununciatlon dated May 17, 1973.

213Molnievicz, L., 'bl_eoretical Inveatiption of the Transition Probabilities in

the Hydrosen Molecule N, J. Chem. Phys., Vol. 51, 1969, pp. 5002-5007. t 214Zernlk, W., "Optical quenchln8 of Matnstabla llydroson", Phys. ltev., Vol. 132, 1963, pp. 320-323. .,

i q974009383-069

215Zernik, W., "Inter_ctfon of Optical and Infrared Radiation with Re,eatable

Hydrogen Atoms", Phys. _ev., Vol. 133, ]q64, pp. AII7-AI20

Addendum: $i_nifican= Papers P,elated Lo Sub__ct Ap2earlng August 1973 - December 1973

Berllnaky, A.J., and llardy,W.N., "Theory of Ortho-Para Conversion and

Its Effect on the NHR Spectrum of Ordered Solid Ortho-Hydrogen",

phys. Rev. B, Dec. 1, 1973.

Constable, J.H., and Gaines, J.R., "Low-Temperature Heat Transport in Solid

liD",Phvs. Rev. 8, Oct. 15, 1973.

Crows, A., and McConkey, J.W., "Experlmental Evidence for New Dissociation

Channels in _!ectron-lmpact Ionization of H2", P_hys.Rev. Lett., Vol. 31, 1973, PD. 192-196.

Eva;m, S.A., and Lane, N.F., "Quantum-Mechanlcal Calculatlon of Inelastic

Cross Secttons for I I_ ....4._ _ Excitation Colltsion_ of

Ground-State He Atoms with He+ Ions", Phys. Key. A_ Vol. 8, 1973,

pp. 1385-1396.

RoechmSeder, H., et 81., "Resonance Structure in _he Excitation Cross Section

by Electron Impact of the 2S-State in Arctic Hydrosen" , Phys. Rev. A,

Nov. 15, 1973.

)Uaktevica, Y.J., et 81., "Lattice Excitations Of the &He (_,_ttm Solids",

Phys. Rev. A, Vol. 8, 1973, pp. 1513-1528.

Roder, H.N., et el., "Survey of the Properties of the Hydrogen Isotopes Below

Their Critical Temperatures", NBS-TN-641 (1973).

klmteder, R.W., "Double- and Tz_lpleophOtOU Decay of Het88table 3Po Atoat_

8tste8", .._, VO1. 7, 1973, Pp, 1458-1468,

Storm0 D., "The Impact Parameter Nethod for Protoa-Rydroaeu Atom Co11181mm.

I, II and Ill", lqt,/lJ. Itev. At I)eo. 1, 1973. 2

•