1982ApJS. . .48. .32 IG © 1982.TheAmericanAstronomicalSociety.Allrightsreserved.PrintedinU.S.A. The AstrophysicalJournalSupplementSeries,48:321-368,1982March ^ow atJetPropulsion Laboratory,Pasadena,CA. © American Astronomical Society •Provided by theNASA Astrophysics DataSystem 6 2-3 + 57 2 -3 + + -7 nitrogen-containing molecules,evolutionofproductmoleculesasafunctionclouddensityand unimportant inthesedensecloudsandareexcluded. (expanded to1067studycarbonandoxygenisotopechemistry);photodegradationprocessesare values by~5X10yr.Manyofthenitrogen-containing moleculesequilibratesomewhatlater.The implications oftheresultsforfutureobservationalwork.Thesegoalsarepursuedwithcalculations temperature, andothertopicsofinterest.Thefullcomputationinvolves328individualreactions to studythedominantchemicalprocessesincarbonandoxygenisotopefractionation,formationof longer thanstatedabove. perhaps afactorof5),andthetimeforchemistryto reach equilibriumcouldthusbeconsiderably nearly allcarbonexistsasCO,evenforrc(H)low5X10cm. determines theratioofHJtoHe(thetwoionswhichgovernvigormolecularchemistry). results ofnotearethefollowing: molecules. Specialattentionispaidtocomparisonoftheresultswithobservationsand evolutionary timesareinverselyproportionaltothe cosmic rayflux(aparameteruncertainto much asanorderofmagnitude.Amongthespeciesshowing wideabundancevariationswithtimeare example, withinthecloudagewindowfrom10to yr,manyrelativeabundanceschangebyas fraction ofthecarbonisneutralanduncombined.Forlowermetalabundances(reducedby10) molecules cmnearlyallcarbonexistsasCOatlatecloudages.Atlowerdensities,asignificant etc.) thanarecommonlyassumedforthedenseportionsofdarkclouds. calculations performedatdifferentabundancessuggestlowerforS,Si,andM(Fe,Mg, constrained atpresentbyobservations,andthereactionsofionswithmetals.Resultsfor C, CH,CN,andCH.Mostofthecarbon-containing moleculeshavereachedtheirequilibrium These resultsareingoodagreement withrecentobservationsofthethreespeciesin the denseregions values: inparticular,muchsmaller abundancesofHCOandCOmuchlarger abundances ofC. including CO,HHCO,CS,CH,CN,OH,HCN, andCH.Modelcalculationsforconditions species ofparticularobservationalinterestbythree-dimensionalgraphicaldisplays.Amongthe that coverawiderangeofdensitiesandtimes;theextensiveresultsarepresentedcompactlyfor the calculationofabundancesdominantisotopescarbon-andoxygen-bearing Subject headings:atomicprocesses —interstellar:abundancesmatter — corresponding tolowelectronabundancesareablepredict theabundancesofanumberspecies, observations ofmolecularlineemissionincolddense clouds.Modelcalculationsforconditions of giantmolecularcloudsin whichhighelectronabundancesaredetermined. corresponding tohighelectron abundances[«(c)/«(H)>fewX10]predict muchdifferent 2 2 2 2 2 4 A detailedmodelofthetime-dependentchemistrydenseinterstellarcloudshasbeendeveloped ii) Theelectrondensityisstronglyinfluencedbythemetalsabundance,aparameterpoorly i) Thechemicalabundancesarequitesensitivetotheelectronconcentration,sincelatter iv) Athighclouddensitiesmanyaspectsofthechemistryarestronglytimedependent.For iii) Fortypicalmetalabundances(asdeterminedinfOph)andforcloud(H)densities^10 In thispaper,thefirstinaseriesofthree,wedescribeformulationchemicalmodeland v) Ingeneral,themodelcalculationsagreereasonably wellwiththeabundancesdeducedfrom 2 THE KINETICCHEMISTRYOFDENSEINTERSTELLARCLOUDS molecular processes Crawford HillLaboratory,BellLaboratoriesandPrincetonUniversity Received 1980November17;accepted1981August27 Crawford HillLaboratory,BellLaboratories William D.Langer 1 M. A.Frerking T. E.Graedel Bell Laboratories ABSTRACT AND 321 1982ApJS. . .48. .32 IG -35 2 + 121316 18 ical processescanbeignored,thechemicalreactions H2(molecules cm)<4X10.Theoreticalstudiesof clouds withsufficientdustscreeningsothatphotochem- (10-50 K)anddensitiesintherange5X10< occur inthermallystableregimesoflowtemperatures tors ofmoleculesandmolecularions.In 322 cant informationoverthepastseveralyears,aswell the chemistryofmolecularcloudshaveyieldedsignifi- lation wehavedevisedhasbroadapplicationtoinves- investigated withoutadetaileddescriptionofinterstellar cipal motivationforthepresentworkistoinvestigate dent chemistryofnitrogen-containingcompoundsin theoretically theprocessesoftime-dependentcarbon suggesting areasrequiringfurtherinvestigation.Aprin- cloud chemistry;asaresult,thecomputationalformu- dense clouds.Neitheroftheseareasinterestcanbe species. Asecondmotivationistostudythetime-depen- and oxygenisotopefractionationinallobservable clouds. tigations ofthetime-dependentchemistrymolecular poses ofbothconvenienceandtractability.Inthepre- larly withrespecttosensitivitystudiesinwhichmetal The emphasisinthelatterisontime-dependent characteristics ofthemostabundantmolecules,particu- that ourresultscanbeindividuallyassessedandgoon sent paperwedescribethemodelinsufficientdetailso companion paper(Langeretal.1982;hereafterPaper to presentselectedresultsandconclusionsofinterest. results ofrelatedobservationalstudies. II) wediscussinmoredetailtheportionsofcalcula- abundance, temperature,cosmic-rayflux,initialioniza- for thenitrogen-containingmolecules,togetherwith tion. Asecondcompanionpaper(Frerking,Langer,and tion state,andinitialclouddensityarevaried.Ina more thandoubledtopermitindividualassessmentof requires thatanextensivereactionsequenceleading dictated almostentirelybythenumberandtypeof Graedel 1982;hereafterPaperIII)presentsourresults tion pertainingtocarbonandoxygenisotopefractiona- from CtoHObeincluded.Thissequencemust carbon andoxygenisotopefractionationindenseclouds carbon andoxygenisotopes. Thestudyofthetime- compound, aswelltoexamine moleculeswithmixed the Cand0 0isotopicformsofeach species thatareincluded.Thestudyoftime-dependent molecules andionsrequires theformulationofreaction dependent evolutionofnitrogen- andsulfur-containing 2 Interstellar cloudsofgasanddustareprolificgenera- Our workistobepresentedinthreeparts,forpur- The complexityofachemicalkineticcalculationis © American Astronomical Society •Provided by theNASA Astrophysics DataSystem II. THECHEMICALMODEL I. INTRODUCTION a) Introduction GRAEDEL, LANGER,ANDFRERKING + + listed byMitchell,Ginsburg,andKuntz(1978)for individual atomsrelativetothatofhydrogenarethose f Oph(seeTable1).Theabundancesforallmolecules ing thetransferofamolecularhydrogeniontonitrogen important respectsfrompreviouscalculations.Themost plausible intermediatespeciesisthatweexplicitlytreat principal Hegenerationreaction: ionized andNOtobeinitiallyneutral.Thefraction 63 differentspecies(126whencarbonandoxygeniso- erations andofconnectingobservedmoleculeswith except Hareinitiallysettozeroinourcalculations.We detail below. Klemperer (1973)andWatson(1973).Thechemistryof oxygen chemistryinourformulationaresimilartothose of heliumthatisionizedestablishedbytheratio assume C,Si,S,andM(=Mg+Fe)tobeinitially and sulfuratoms.Theseaspectsarediscussedinmore significant differenceistheomissionofreactionsinvolv- silicon, sulfur,andnitrogen,however,differsinmany that haveevolvedfromtheearlyworkofHerbstand topic variantsareincluded)inourcalculations. sequences involvingNandS.Theresultoftheseconsid- and theprincipalHedestructionreactionat/=0: 2 A convenientreferencefortheabundancesof The basicaspectsoftheion-moleculecarbonand + cosmic ray(CR)+He^eCR, -5 + a 4 +6 +-5 +-6 13+6 187 16-4 12+-4 13+18 positive ionabundances.Theinitial ioniza- lated asdescribedinthetext.The electron N 4.28X10 cussed inthetext. oxygen isotoperatiosandHe is calcu- He 0.28 Elemental Abundances(relativetoH) abundance issetequaltothesum ofthe are setbythechoiceofcarbonand e 1.69XHT M 2.58XHT S 1.66X10 tion statesareindicatedhere and dis- Si 1.66X10 C 2.24X10~ 0 7.04X1CT 0 3.52X10 C 1.46X10 1978 forfOph,exceptthatCand0 2 a ValuesarethosegivenbyMitchelletal. + He +H->He+H+H. 2 Element Abundance h) InitialConditions TABLE 1 Vol. 48 1982ApJS. . .48. .32 IG -3 9 -35 2 1618 1213 17- ion abundances. gas phaseandisformedalmostexclusivelyongrains. ular formrequiressomediscussionbecausecloudscon- The electronabundanceissettothesumofpositive has formed,whichisthepointincloud’sevolution Thus, ittakesseveralmillionyearstoproducesubstan- for thismechanism.Thecharacteristictimescale (Spitzer andJenkins1975)providestrongsupport Molecular hydrogencannotbemadeefficientlyinthe No. 3,1982 what uncertain,butobservationalconstraintsputcer- cm. Thegasphasechemistrydoesnotproducemole- grains is~10/«yr,wherenthetotalgasdensity. converting hydrogenfromatomictomolecularformon are inexcellentagreementwiththeoreticalmodels Observational studiesofHabundancesindiffuseclouds tain primarilyatomichydrogenwhentheyfirstform. in shieldedregionsofdensecloudsisaccomplishedby cules efficientlyuntilperhaps20%ofthegasisH,and cosmic-ray protons.Thefluxoftheseprotonsissome- fractionation isofconcern).Ionizationneutralatoms range coveringthatfoundindenseclouds(Martinand at whichwechoosetobeginourcomputations. this moleculeformationisdelayeduntilsubstantialH tial amountsofHinalowdensitycloudwithn«100 tain boundsonitsvalue(Wootten,Loren,andSnell molecules cmtoahighof2X10, (in mostcases,molecularabundancesarenotsensitive characteristic ofregionswithoutnearbyenergysources Barrett 1977).Weadoptatemperatureof10Kas several calculationsvariousvaluesfromalowof5X10 between calculationsthatincludeallreactionsthought in Table2.Thischemicalsetrepresentsacompromise ent cloudsandindifferentmolecules.Wehavechosen to temperatureovertherange10-40Kunlessisotopic pounds, forexample)buthave madealternatepathways possible indarkcloudsandcalculationsthatincludeso II; Penzias1980;Wilson,Langer,andGoldsmith1981). representative ofmanythemeasuredratios(seePaper 65 and0/=500,valuesthatseemreasonably ous sincearangeofvalueshasbeenmeasuredindiffer- to performthebulkofourcalculationswithC/= chemical diversityofthespecies treated(noCNcom- few chemicalpathwaysthat resultsareseverelycon- scribe theinteractionsamongspeciesarepresented 1X10“ sformostofourcalculations. 1982; Guélin,Langer,andWilson1982);weuse^= strained bythereactionchoices. Wehavelimitedthe available tothosespecies that weinclude,thusper- 2 2 2 2 xy The assumptionthatallhydrogenisinitiallyinmolec- As initialconcentrationsforH,wechoosethe The choiceofratiosfortheisotopesisnotunambigu- The chemicalprocessesthatwehavechosentode- 2 © American Astronomical Society •Provided by theNASA Astrophysics DataSystem c) ChemicalReactionsandRateParameters i) GeneralRemarks DENSE INTERSTELLARCLOUDCHEMISTRY 2 -1 3-1 -931 + + wide rangeofchoicesimportantphysicalparameters. including morereactions(see§III),yettheyaresuffi- printed inboldfacetypecompriseatleast5%ofthe branching ratiosforcompetingchannels.Fortheprin- defined asonewhichisobserved orwhichchemicallylinksthose indicated inTable2,sincereactionswhosenumbersare ciently tractabletopermitusexploretheeffectsofa error whencomparedwiththeresultsofcalculations cipal chemicalspecies,ourselectionsintroducelittle mitting abundancesandrateparameterstodictatethe cipal species. ray ionization,whichcarriesunitsofs.Rateparame- posed ofincreasinglylargernumbersatoms.Within that areobserved. chemical methods.Theimportanceofareactionisalso set byanalogywithsimilarreactionsortheoretical total formationorremovalchannelforoneoftheprin- are indicatedby“M”inthestatuscolumn;others ters thathavebeenmeasuredinlaboratoryexperiments and areincmmoleculessunits,exceptforcosmic- given astheA,B,andCcoefficientsof exception beingmadeforH.Therateparametersare groups, thelistingofcompoundsisalphabetical,an reactions andproceedtoofmoleculescom- Prasad andHuntress(1980a),whobeginwithatomic with anyotherconstituentoftheinterstellargasin They thereforehaveaverysmallprobabilityofreacting reactions thosesequencesofthatproceed (at theLangevinrate,about10cmmolecules). we haveadoptedarediscussedbelow. ions OHandreactwithH,whereastheion intermediate ionsinourcalculation.Forinstance,the dense molecularclouds.Wewillthuswriteassingle through ionsthatreactpreferentiallywithH.The H0 doesnot.Therefore,thesequenceofreactions, (2) theseionsreactonlywithH.Exceptforafew that (1)therapidreactionsoccurinstantaneously,and at allwithH.Thisapproachisequivalenttoassuming sequences endwithanionthatdoesnotreactrapidlyor species ofinterest,wedonotexplicitlyincludethese 2 2 2 3 2 2 2 For thepurposeofthisselection, a“principalspecies”is The orderingofTable2followstheapproach Many molecularionsthatreactwithHdosorapidly Important aspectsofthechemicalformulationthat 2 ii) AbbreviatedReactionSchemeforMolecularIons + H++O^OH+H, 2 -103 8X10 cmmolecules,(1304a) BcT k =ATe-/ 323 1982ApJS. . .48. .32 IG Reaction Number 106 102 107 103 101 120 202 151 205 203 201 152 208 207 206 199 156 154 153 215 211 210 209 204 159 158 157 155 220 219 216 214 213 212 231 221 218 217 160 229 227 226 225 223 222 230 228 224 © American Astronomical Society •Provided by theNASA Astrophysics DataSystem - +- +- +- — + _ +- + +- — +- +- +13 1312 +13 +12 + + + - +13 + +1313 +1212 +12 12+ +12 +13 +12H + 13+ +13 + +13 +12 12 +12 + + +13 +12 +13 N +CR—N+e Cosmic RayIonization S +GRAIN 0 +GRAIN N +GRAIN H +CR—H/e He +CR—»e“ H +CR—H+e Si +GRAIN He+GRAIN H +GRAIN H +GRAIN— H +CR^H+e Grain Reactions H+ GRAIN H+ +O—0+H M +GRAIN H+ CH- H++ C H+ C, H +C H"’” +Si—»H H+ +S—S+H H +M—► H Reactions e +GRAIN- H+ CH- H +OH H +CS2H H +CS2H H+ CH- C+GRAIN h +cs- H++ Irisch. H +C H+ C- H +0—»Oj" H+ +NO H+ +NH C+GRAIN H+ CH^CH^ H +0- h +cs- H+ CH- H^ +H,«)- H+ CH, h +nh- H +NH, h +co h +co H +CO 2 2 3 2 2 2 2 2 3 2 2 2 2 2 2 + + 12 + + » NO+H ♦ nh/+h » ho+ 12 13 ^ CH^+H H0 +2H NH +2HH 3 3 3 13 12+ 13+ 12 -12 CH^ +2HH CH^ +2HH 13+ 12+ 13+ 12 2 13 2 12 12 13+ >hcs+ +h ► hcs+ CH +2HH CH^+ 2H+H 1213 3 ^C+GRAIN »hco +h<, »hco +h »hco +h ► hco++ - ch^ +h ch^ +h 2 2 2 ch^ +h ch +h 2 13 2 3 -> H+GRAIN - S+GRAIN ^ Si+GRAIN -0 +GRAIN -► N+GRAIN CCH^+2H +H GRAIN 2 1213 — C+GRAIN cch^ +h ^ He+GRAIN Interstellar CloudChemistryReactionsandRateParameters H +GRAIN M +GRAIN + H + H Chemical Reaction TABLE 2 324 -9 —9 -9 -9 -9 —9 -9 -9 -9 -9 -9 -9 9 -9 -9 —9 —9 -9 -9 -9 -9 —9 —9 —9 —9 —9 -9 -9 -9 2.1X10 5.2X10 3.4X10 3.4X10 2.9X10 8.2X10 2.8X10 1.0X10 8.0X10“ 1.0X10 1.0X10 7.0X10 1.0X10 2.8X10 3.0X10 ^ 3.0X10 3.0X10 2.1X10 3.2X10“ 1.2X10“ 3.5X10“ 3.8X10“ 2.0X10 ■ 1.2X10 5.1X10“ 5.4X10“ 2.0X10' 5.7X10“ 5.7X10" 1.0X10 1.0X10 5.0X10 5.0X10 1.9X10 1.9X10 1.2X10 1.2X10 1.2X10 1.0X10" 1.9X10 1.0X10 1.3X10 1.1X10 4.7 .09 2.8 1.5 1.5 A -9 -10 Rate Parameters 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 B C 232. FS71 Status M KTH74 M HKT74 M HKT74 M FF73 PH80A PH 80A PH80A PH80A This work;butsee§IIc.v. PH80A;f26 PH80A;fl PH80A =R(229) = R(227) =R(225) PH80A = R(221) PH80A = R(216) PH80A =R(219) PH80A =R(216) PH80A PH80A See text;§IIc.ix. R72,F73 See text;§IIc.ix. See text;§IIc.ix. See text;§IIc.ix. See text;§IIc.ix. See text;§Uc.ix. =R(210) =R(208) See text;§IIc.ix. See text;§IIc.ix. =R(205) See texf;§IIc.ix. See text;§IIc.ix. See text;§IIc.ix. =R(205) FGK79;flO f4 This work;§IIc.iv. f4 GL74 GL74 References, remarks 1982ApJS. . .48. .32 IG Reaction Number 390 302 301 303 305 304 309 307 308 306 311 310 316 313 399 398 312 320 319 318 317 323 322 324 321 334 337 332 331 330 327 328 326 325 338 336 335 353 352 349 354 351 342 341 340 348 346 344 347 350 345 © American Astronomical Society •Provided by theNASA Astrophysics DataSystem + + + +13 +13 +13 +131212 +131212 +12 +12 +13 +12 +12 +12 +12 + +13 + + + +13 + +13 + +12 +12 +12 +12 +12 +,2 +,213 +12 + +,2 +13 +,2 +,2 +l3 +13 +12 +l3 + +13 +,3 +13 +13 +12 + +13 +,2 +13 He +H He +Si—-I- He+ +M—>M+He He Reactions He +C^C+ He +CN—CN He +CH^C+H He +C^ He +CC+ He +C—C+ He +CN^CN He +CO—CO He +CH—CH He +CO^CO He +CS—S+C He +CS^CS He +NO—NO He +CS- He +0O He +NH—>NH He +N— He+ CS- He +N He+ CH— He +NO—►0N 2 He +HNC- He+ HNC- He+ HCN- He+ HCN- He +HCN- He +HCN- He+ CCH He +CH-h He +OH—♦0-fH 2 He 4-CH He+ CH- 2 He +HNC- He+ HNC- He +HCN- He +HCN- He +0C5 He +HNC- He -fNH He4- HNC- He +HNC- He +HNC- He +HCN- He +0CS- He +H,0—H0 He+ HCS- He+ HCS- He +HCN- 2 2 2 2 2 2 2 2 3 + > NH+He 2 +13 13+ + ► S+CHe ^ C+He4-S > NH+He3H 3 13 +13 13+ 13 13+ +12 12+ 12+ 12+ +12 12+ 12 l2+ 13+ 12+ +13 13+ 13 ,2+ +12 1213 13+ 12+ I3+ ,2+ - C++NHHe -N+ CHHe -HCN +He3H - CH^+2HHeN -C +NHHe -N+ CHHe -HCN+He 3H - CH+NHe2H -> C+NHHe -N+ CHHe - HCN+He3H - CH^+NHe+2H - C+NHHe + HCSHe ♦ HCS+He -N +CHHe - HCN+He3H - CH^+2HNHe »HCXD+He S ► S+COHe 2 2 3 2 2 ^ CCH^+He2HH CH+He CH +HeH CH+ He2H CH+ He2H 3 3 2 2 Chemical Reaction TABLE 2—Continued 325 10 10 10 10 10 -10 —13 10 10 10 -10 10 10 10 10 10 10 10 -9 9 -9 9 —9 9 9 9 9 9 9 9 9 9 9 9 9 -9 9 9 -9 9 9 9 9 9 9 9 9 9 8.1X10 “ 3.7X10 “ 8.1X10“ 8.2X10 8.2X10 “ 7.5X10 “ 8.1X10 1.5X10 8.2X10 “ 8.2X10 “ 7.5X10 “ 8.1X10 9.8X10“ 9.8X10“ 4.4X10“ 9.8X10“ 9.8X10“ 2.0X10“ 7.6X10“ 7.6X10“ 3.3X10 1.6X10 “ 3.0X10 2.0X10“ 1.6X10 3.0X10“ 3.0X10“ 2.0X10“ 1.8X10 “ 1.8X10 “ 1.8X10 “ 1.9X10 “ 1.8X10 “ 1.0X10“ 1.0X10 “ 1.0X10“ 1.0X10“ 1.1X10 1.0X10“ 1.6X10“ 1.1X10 1.9X10“ 1.9X10 1.3X10“ 1.6X10“ 1.1X10“ 1.1X10“ 1.3X10“ 1.0X10“ 1.9X10“ 1.4X10“ -9 -10 Rate Parameters B C Status M M M M M M M M M M JCB80 PH80A PH80A fll PH80A PH80A This work This work H77 PH80A PH80A H77 H77 PH80A H77 H77 H77 PH80A =0.5*R(303) = 0.5*R(303) = R(303) PH80A PH80A;fl H77 H77 H77 H77 PH80A = R(309) = R(307) PH80A KH75A = R(313) = R(330) = R(314) = R(311) = R(330) = R(332) = R(324) = R(337) = R(332) = R(331) = R(337) = R(332) = R(337) = R(331) = R(330) = R(328) = R(324) = R(331) = R(349) References, remarks 1982ApJS. . .48. .32 IG 440 437 435 434 439 438 436 433 432 431 430 427 424 420 Reaction 429 428 426 425 423 422 421 418 417 415 414 412 411 410 408 407 405 404 402 401 365 419 416 413 409 406 403 363 361 364 362 359 358 360 355 356 Number 357 © American Astronomical Society •Provided by theNASA Astrophysics DataSystem +13 + + + + + + 12+ 12+ 12 12+ 12+ 12+ 12+ 12 + + ,2+ n 12 12+ 12+ 12+ 12+ 12+ 12+ 12+ 12+ 12 12+ 12+ 12+ 12+ 12+ 12+ 12+ 12+ 12+ 12+ ,2 12 12+ 12+ 12+ ,2+ 12+ 12 12+ 12+ He+ CH, He + He + He + He + He+ He +NH. He + c + c + c+ + c + c + c + c + c+ + He + He + c-f c+ + c+ + c + c + c + c + c + C Reactions c + c + c+ + c + c + c + c + He+ + c + c + c + c + c + c + C+ + c+ + c + c + c + C + c + C+ + C + c + 13 13 12 h3 12 12 13 13 12 1313+12 13 12 NH +12 1312 12 12 13132+ +12 12+ 13132+ 121¿ 13 13+12 12+ +12 12 12 12+12 12+ 12+ +12 12 13 12 131213 12 13cH 1213 13 13 13 12 12 12 13cH hcs- HCO HCX) cs - hcs - hcs - ocs- ocs ch, - 2 2 2 2 2 2 nh - nh - h,co —h+ch hco hco . Si —+C HCO ^CH^+ Hœ hco hnc^ ccn+h o —o+co o-^hco + HCN ^C+ hnc ^n^+h hco hco —h+c OH —HCO+2H NO ^+C NH — hcn Hœ hco —Hœ+< ho —hco+ H, —CH+H M ^+C ch. ch ch ^ CH ^CCH/+2H ch - 2 cch co - ch - ch - ch - ch - ch 2“ 3 3 2 2 2 2 2 2 2 2 2 3 3 2 2 2 2 + - 12+ 1213 ,2 12+ ^ NH+He 3 13+ 12+ 13 +12 12+ 13 12 13+ 13 ♦ NHj ♦ HCN+ _ 13+Uqq ^ CCH^+H -ch+- 2 HCN +3H C+ 2 12+ 1312 2 1312 12+ 12 1213+ - CH+HeS ^ CH+HeSH + S++CHHe ^ S+CHHe - HCO+He > CH^+HHe > CH^+HHe ♦ HCO+HeS ♦ S++CO+He 12+ 12+ 1312 12+ 12+ 3 3 2 2 2 2 2 12 13+,2 12 l3+ > ch+c-fh • ch^++h CH/+ C+2H CH+ C+2H CH^+ 3H cch- 3 2 12+13 12+ 12+12 3 2 2 • cn- ' CN+H ► hco++c ► hco+c ► ch+coh 2 2 2 2 3 CH^ +2H ch+ ch ch^+ +h HCO +He 2 3 2 2 CH+ CO+2H CH+ CO2H Hœ+ ch 3 3 1213 cch^+ +h 12 c Chemical Reaction + H 3H TABLE 2—Continued 326 10 —10 —10 10 10 10 —10 10 —10 -10 -10 9 9 9 9 9 —9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 -9 —9 —9 9 9 9.0X10 " 9.0X10 8.2X10 8.2X10 5.2X10 " 4.0X10" 8.0X10" 8.2X10 5.2X10 " 8.2X10 7.6X10 1.0X10 5.2X10 7.6X10 2.2X10 " 2.0X10 3.2X10 " 2.0X10 2.2X10 " 2.7X10 " 2.0X10 " 2.2X10 3.2X10 2.0X10 " 2.0X10“ 2.0X10“ 2.0X10 “ 2.0X10“ 2.0X10“ 2.0X10 " 1.2X10 " 1.0X10 " 1.1X10“ 1.4X10 " 1.2X10“ 1.0X10" 3.2X10" 1.0X10" 1.4X10 " 3.2X10" 1.0X10" 2.0X10" 1.0X10“ 2.1X10 1.0X10 “ 1.0X10 1.8X10 1.8X10 1.1X10 1.0X10" 1.0X10" ï-9 ^-9 -10 -16 -9 -9 -9 -9 -9 -10 Rate Parameters B C Status M M M M M M M M M M M M SA80; f25 PH80A PH80A AHF76 AHF76 AHF76 H77;SB79 PH80A PH80A AHF76 AHF76;fl PH80A PH80A PH80A PH80A AHF76 AHF76 PH80A fl2 PH80A PH80A AHF76 PH80A PH80A V80 PH80A KH75A = R(426) PH80A PH80A;fl PH80A = R(426) = R(426) = R(423) = R(405) =R(431) = R(422) = R(4I9) = R(417) = R(414) = R(404) = R(435) = R(414) =R(436) =R(437) = R(363) = R(361) = R(359) = R(357) = R(354) =R(353) References, remarks 1982ApJS. . .48. .32 IG Reaction Number 502 501 505 503 509 507 506 504 619 613 514 513 512 511 510 508 612 611 609 608 606 605 604 601 599 515 610 607 603 602 520 519 518 516 533 532 531 530 528 523 522 521 540 539 538 537 536 535 534 529 527 526 525 524 © American Astronomical Society •Provided by theNASA Astrophysics DataSystem ,3+ + +12 + + +13 +12 +13 + + +13 +12 l213+12 + +1 313 3+ 3+ 3+1 3+ 3+ 3+1213 312 312 313 313 313 313 3+12 3+1213 312 3+13 3+ 3+12,3, 3+,13 3+113 3+ 3+13 3+13 3+121 3+12 3+,2 3+12 3+,3 3+13 3+13 3+113 3+121312 3+1213 3+113 3+12 312 3+13 313 3+,3 C Reactions N +O,^0NO N+ C- N +0—► N -I-0^NO+O N+ CN- N+ CN- N+ +Helle\2q+13 N+ C- N+ H- N +Si- N+ CO- n+ œ- + nc—CCN N+ +M—N N ,O''Reactions 2 2 2 CN 2 2 N+c C+ +M—M++C C +OH c +o c +o—Hœh C +NO C +NH C +co—c c+ +ch c+ +ch C+ +CH C+ +CH C+ +HCH/ C+ +Si^Si+C c+ ch C -1-HN^CN+H c++ ch c +h- c +nh- C +HCN^ c +hn—nh c +hco^ c +ho c+ ch c+ ch c+ ch C +Hœ C -hhco c +hco C +NH^HCN c +nh^ c+ ch, C +HCN—N C +HCO—CHœ2H c +hco^Hœ C +HCO—CH-1-2H c+ ch c++ ch c +hco c+ +hco c +hco 2 2 2 3 2 2 2 2 2 0 2 2 2 2 32 3 2 3 3 2 2 2 2 2 + + - NH+3H > Si+N 3 13+ +13 +13 13+ 13+ 12+ 13 12+ -HCO+ 2H ^ o+co 13+ 12+ 13+ 1213 I3 ^ NO+C ► HCN+3H ♦ HCN+N2H >HCN +N2H ► hco++n ► HCO+N 2 2 2 C+ CN C+ CN 13+ ► HCN+2H ^ CCH+H — CH^+H 2 2 2 1213 1213 12+13 13 13+ HCO + 13+ 1313 13+ 12+13 12+13 13+ 13 1213 13 1213 ■ ch^++h CCH^+ 3H CH3 +C2H CH^+ 3H CH+ C+2H 2 2 3 ► ch+coh ► hco++ch ► Hœ+c ► hco+c ► hco+ch 13+12 ch+ ch CH^+ H+ ch^"+ c+h ch^+ +h 3 2 2 CCH^+ 2H 3 2 2 ch+ coh 1213+13 3 cch+ h 2 Chemical Reaction TABLE 2—Continued 327 10 _10 10 -16 10 10 n 10 10 9 9 9 9 9 9 9 -9 9 9 9 9 9 9 -9 -9 9 9 4.0X10“ 8.0X10 5.2X10 “ 1.0X10 9.0X10 9.0X10 5.2X10 “ 5.2X10~ 4.8X10' 3.0X10 “ 2.7X10“ 3.0X10“ 2.0X10 “ 4.9X10 2.0X10 ~ 4.9X10 5.0X10 2.0X10 “ 5.0X10 2.0X10 “ 2.0X10 “ 2.0X10 “ 2.0X10 “ 2.1X10 2.0X10 “ 2.0X10 “ 1.0X10“ 3.2X10 2.7X10 “ 2.2X10 2.0X10 3.2X10 “ 2.0X10“ 2.2X10 1.1X10 1.1X10 3.2X10 1.2X10 1.0X10 3.2X10 1.0X10“ 1.0X10 1.4X10 1.2X10 1.0X10 1.4X10 1.0X10“ 1.0X10 1.0X10 1.1X10“ 1.1X10 1.0X10 1.2X10 1.2X10 9 n-9 3 “ 1-9 -10 -10 -10 -9 -9 -9 -9 -9 -9 -9 -9 -9 -9 -9 -9 -10 Rate Parameters B C Status M M M SA80; f25 = R(404) = R(402) = R(410) =R(409) = R(405);f2 = R(404) = R(405) =R(403); fl2 = R(401) = R(412) = R(411) = R(413) 0.5*R(604) 0.5*R(604) PH80A = R(415);f2 = R(415) = R(414) R72;PH80A;F73 = R(419) = R(417) A79 A79 PH80A = R(417) A79 H77 KTH75B = R(422) = R(421) = R(419) = R(430) = R(426) = R(426) = R(426) = R(423) = R(422) = R(423) = R(601) = R(437) = R(435);f3 = R(434) = R(431) = R(431) = R(426) = R(604) = R(436) = R(437);f3 = R(436);f3 = R(433) = R(435) = R(610) = R(608) References, remarks o
TABLE 2— Continued Reaction Chemical Rate Parameters References, l_0 Number Reaction B C Status remarks a 12 + i2 614 N+ + H2 CO ^NH3 + CO + H 1.3X10“ PH80A 13 + 13 -9 615 n+ + h2 co ► nh3 + œ + H 1.3X10 = R(614) 651 0+ + M ■» + O 2.9X10“ M R72;PH80A;F73 652 0+ + Si > Si+ + O 2.9X10 -9 = R(616) + + 653 0 + H, H30 + 3H 1.6X10“ M KTH75B + -12 654 0+ + N2 NO + N 1.2X10 M D68 655 0+ T NH, » NH^ + O 1.0X10 -9 B75
Metal Ion Reactions 701 Si+ + M —► M+ + Si 2.9X10“9 PH80A 711 S+ + M — M+ + S 1.0X10-9 PH80A 712 S+ + Si ^ Si+ + S 1.6X10-9 PH80A 713 s+ + h12co h12co+ + s 3.6X10”10 PH80A 714 s+ + h13co — h13co+ + s 3.6X10”10 = R(713) 715 s+ + h12co — sh+ + 12œ 3.6X10 -10 PH80A 716 S+ + H13CO SH+ + 13CO 3.6X10 -10 = R(715) + 12 12 + 717 S + CH3 ^ H CS + H 1.0X10“ PH80A + 13 13 + -11 718 s + ch3-^h cs + h 1.0X10 = R(717) + + 719 S + NH, ^ NH3 + S 1.2X10“ M LH73 SH + , OJ“ Reactions + + 801 SH + O - » S + OH 2.9X10 -10 PH80A + + -9 821 o2 '+- M --> M + 02 1.2X10 R72 822 of + N - - NO+ + O 1.8X10”10 M G66 823 of+ S- S+ 5.4X10“10 PH80A * + + °2 9 824 of- Si — Si + O0 1.6X10“ PH80A 12 12 + 9 825 of + h2 co ► h2 co + o2 1.0X10“ PH80A 13 13 + 1.0X10 ”9 826 of + h2 co - ► h2 co + o2 = R(825)
HCO“1" Reactions 1001 H12CO+ + M^M++ 12CO + H 2.9X10“9 See text 1002 h12co+ + S —+ SH+ + 12CO 3.3X10”10 PH80A 1003 h12co+ + si ^si+ + n12œ 5.0X10”10 PH80A 1004 h12co+ + 13co — h13co++ 12co 6.8X10”10 SA80; f25 1005 h12co+ + 12cs — h12cs++ 12co 1.3X10”9 PH80A 1006 h12co+ + 13cs — h13cs++ 12co 1.3X10”9 = R(1005) 1007 h12co+ + NH —> NHf -f 12CO + H 6.4X10”10 PH80A 1008 h12co+ + 12CH2 12CHf + 12CO 8.7X10 ”10 PH80A 1009 h12co+ + 13cH 13CHf + 12CO 8.7X10“10 = R( 1008) 12 + 12 2 12 + 12 9 1010 h co + h cn h2 cn + co 4.0X10 ” M H77 12 + 12 12 + 12 9 1011 h co + hn c h2 cn + co 4.0X10 “ = R(1010) l2 + 13 13 + 12 -9 1012 n œ + h cn h2 cn -h co 4.0X10 =R(1010) 12 + 13 13 + 12 -9 1013 h co + hn c H2 CN -f- CO 4.0X10 = R(1010) 12 + 12 10 1014 h co + nh2 — NHf + CO 8.9X10 ” PH80A 12 + 12 12 + 12 9 1015 h co + h2 co ^ h3 co + co 3.3X10 “ PH80A 12 + 3 13 + 12 9 1016 H œ + h2 co ► H3 œ + œ 3.3X10 ” = R(1015) 1017 h12co+ + NH3 »NHf + 12CO 2.6X10 -9 H77 1051 h13co+ + M —♦ M“1“ + 13CO + H 2.9X10”9 = R( 1001) 1052 h13co+ + S —» SH“*" + 13CO 3.3X10“10 =R(1002) 1053 H13œ+ + Si —» Si+ + H13CX) 5.0X10 -10 =R( 1003) 1054 Hl3CO+ + 12co ^ h12co++ 13co 2.9X10“10 M SA80; f25 1055 h13co+ + 12cs^h12cs++ ,3co 1.3X10”9 = R(1005) 1056 h13co+ + 13cs^ h13cs++ 13co 1.3X10”9 =R(1005)
328
© American Astronomical Society • Provided by the NASA Astrophysics Data System 1982ApJS. . .48. .32 IG + Reaction Number 1188 NH, NH0Reactions 1189 1187 1184 1186 1185 1183 1182 1103 1062 1058 1057 1181 1172 1171 1170 1169 1168 1167 1166 1165 1163 1162 1066 1065 1064 1063 1061 1060 1059 1164 1116 1113 1112 1109 1104 1102 1101 1067 1161 1115 1114 1111 1110 1108 1107 1106 1105 32 © American Astronomical Society •Provided by theNASA Astrophysics DataSystem +13 +12 + +,313 +12 + + + 13+ +12,2 +13 + + +13 + +12 +13 +12 +12 + +13 1212 +1313 +13 + + +1313 +12 + 12 NH+ +1212 +12 + +13 13+ 13 I3 13 13 13 13 13 13+ 13 13 oh +Hœ^co oh +cx)—Hœ oh + oh +ch^ oh-i- ch oh +oho+ oh +s- oh +- N.H+ +H,CO^N-> nh +co nh+ cs- nh +nh- NH +NH—NH. nh+ ch- NH +NH—► nh+ cs- nh+ co nh+ co nh+ ch- NH + NH, +H.CO NH.+ +H.CO^NH/+H NH +HNC^NH^CN nh+ ch- NH +S^SH nh +ho- nh +hcn^nh/ nh +hcn- NH +—►NH4N NH++ CH 3 NH nh +hnc^NH^cn nh+ ch- NH +H nh+ ch hco + hco+ + hco+ + hco+ + hco+ + hco+ + hco+ + hco+ + hco + hco+ + hco+ + 23 23 2 23 2 23 2 2 23 2 23 2 2 2 2 2 2 2 3 3 32 2 32 3 3 3 3 3 32 3 3 o '"2 TI12’1^114 3 + M + Si 13 -13 13 12 121213 1313 1313+ -NH+l 1213 13+l3 2 + NH —NH^+CO NH NH —»NHj+COH Hœ hnc hcn cn++co + hnc hcn++co hcn +co ch^ ch^+co ch-+ CO 3 0 2 2 2 2 2 23 ^ SH+O. ► ho+ 32 Si+ +NH M+ + 13+ 12 13+ 12+ 13 ♦ nh/+nh » NH/+OH H+ +O. 2 ► ho+ » NH^+n 12 13+ 32 ^hcs +n. »hcs+ +n -hco +n - hco+n »NH/+ C 2 2 2 2 12+ -NH+- -nh/+ cn • ch+nh NH, 12+ 13+ 12+ 32 13 12+13 +13 ch +nh + N. ch +o. 32 ch +n ch +n NH/ +HCO ^hcn+ œ 3 32 32 +12 nh +œ 2 13+ 3 NH. + C »Hœ+ co 4 3 + N,H + N. Chemical Reaction '2 TABLE 2—Continued 329 10 10 10 10 10 10 10 10 10 1U 10 10 10 10 10 10 10 1 13 10 1 1 1 9 9 9 9 9 9 9 9 9 9 9 9 8.7X10 “ 6.4X10“ 6.2X10 9.6X10“ 6.9X10“ 8.7X10 “ 9.9X10" 6.4X10" 8.8X10 “ 8.9X10“ 9.9X10" 8.2X10" 8.6X10" 6.1X10" 8.9X10" 8.7X10“ 6.4X10“ 8.8X10 “ 5.0X10“ 7.1X10 “ 6.9X10“ 8.7X10 “ 8.8X10 9.6X10“ 8.6X10" 8.8X10 “ 5.0X10“ 1.0X10“ 1.0X10 “ 1.1X10“ 1.0X10“ 1.0X10“ 1.0X10“ 4.0X10 “ 4.0X10 “ 4.0X10 “ 3.3X10 “ 3.3X10 “ 4.0X10 “ 3.2X10 “ 2.6X10 “ 3.3X10 ~ 3.2X10 2.3X10' 1.9X10 “ 1.1X10 1.1X10“ 1.1X10“ ï—9 -10 -9 -9 -10 Rate Parameters B C 200. Status M F79;PH80A;KTH75B M M M KTH75A;fl5 M M M PH 80A PH80A PH 80A PH80A PH80A PH80A PH 80A PH80A =R(1010) H77 = R(1010) = R(1008) =R(1008) =R(1007) PH80A PH80A PH80A PH80A f23 H75 HP73;H77 H77 =R(1010) PH80A PH80A PH80A PH80A PH 80A H77;fl4 = R(1015) = R(1015) = R(1014) = R(1010) = R(1104) = R(1017) = R(1188) = R(1114) = R(1109) = R(1185) = R(1170) = R(1164) = R(1162) = R(1109) = R(1109) = R(1107) = R(1167) References, remarks o 00C\] GO TABLE 2— Continued Reaction Chemical Rate Parameters References, |-D Number Reaction B C Status remarks a CTico Hj" Reactions
12c 12 10 1301 H 3+ - CH^ + 2H + H2 8.0X10“ =R(1304) 13 13 10 1302 H^+ C CH^+2H + H2 8.1X10 “ = R(1301) + + 9 1303 3 + M - ► M + H + H2 2.0X10 “ PH80A + 10 1304 3+ + 0- H30 + 2H + H2 8.0X10“ M F76 1305 3* + S —► SH+ + H 2.0X10 “9 PH80A + 9 1306 3" + Si ■ » Si + H2 + H 3.7X10 “ PH80A 12 9 1398 H + 12C c2h^ + h + h2 1.7X10 “ PH80A H3+ + 13 2 ' 13 9 1307 3 + C2 - c2h^ + h + h2 1.7X10 “ = R(1398) + 13 12 12 13 9 1308 h3 + C C- c ch^ + h + h2 1.7X10 “ =R(1398) 12 12 + 9 1309 H + CH ch3 + h + h2 1.2X10 “ PH80A 13 13 9 1310 H3" + ch ch^ + h + h2 1.2X10 “ ==R(1.29) 12 12 + 9 1311 H + cn h2 cn + h2 + h 1.0X10 “ PH80A + 13 13 + 9 1312 h3 + cn - ♦ h2 cn + h2 + h 1.0X10“ = R(13in + 12 12 + 9 1313 h3 + co > H CO + H, 1.7X10 “ M KTH75A 1314 Hi + 13CO — H13CO+ + H. 1.7X10 “9 = R(1313) + 12 12 + 9 1315 h3 + cs - *h cs + h. 2.9X10 “ PH80A 1316 + 13CS — H13CS+ + H, 2.9X10 “9 = R(1315) 1317 -N, ♦ + H, 1.7X10 -9 M KTH75A + 1318 H3 + NH - NH7 + H, + H 1.3X10' PH80A + + -9 1319 H3 + OH - - h3o + H + h2 5.9X10 PH80A + + 1320 h3 + o2- ♦ o2h + h2 6.4X10" M KTH75A; fl5 12 12 -9 1321 h/+ c2h c2h^ + h2 1.7X10 PH80A 13 -9 1322 H + + 13C H - c2hí + h2 1.7X10 = R(1321) 3+ 12 123 12 13 9 1399 h3 -h c ch ■ c ch^ + h2 1.7X10 “ = R(1321) + 12 12 + 9 1323 h - ch2-^ ch3 + h2 1.7X10 “ PH80A 3+ 13 13 9 1324 h3 + ch2 ^ ch^ + h2 1.7X10 “ = R(1323) 12 12 + 9 1325 + H CN - >h2 cn + h2 7.0X10 “ M H77 + 12 12 + 9 1326 h3 + hn c »h2 cn + h2 7.0X10 “ = R(1325) + 13 13 + 9 1327 h3 + h cn - ♦ h2 cn + h2 7.0X10 “ = R( 1325) + 13 13 + 9 1328 h3 + hn c- ♦ h2 cn + h2 7.0X10 “ = R(1325) + 12 2 + 9 1329 h3 + h co- >h¡ co + h2 1.0X10“ PH80A 13 3 + 9 1330 H3" + h co - >h¡ co + h2 1.0X10“ = R(1329) + + 9 1331 h3 + h2o - » h3o + h2 5.9X10 “ M KTH74 + + 9 1332 h3 -h nh2 - - nh3 + h2 1.8X10 “ PH80A 1333 h^ + o12cs » H012CS+ + H. 2.1X10 -9 PH80A + 13 13 + 9 1334 h3 + o cs ho cs + h2 2.1X10 “ = R(1333) + 12 12 + 9 1336 h3 + ch3 - ch5 + h + h2 2.1X10 “ PH80A; fl6 13 13 9 1338 H3" + ch3 - ch^ + h + h2 2.1X10 “ = R(1336) + 12 12 + 9 1339 h3 + h2 co- -h3 co + h2 6.4X10 “ PH80A 13 13 + 9 1340 h^ + h2 co- ^h3 co + h2 6.4X10 “ = R(1339) + + 9 1341 H3 + NH3 — NH3" + H2 + H 2.0X10 “ M KTH74 3 + 9 1342 H3+ + nh3- nh4 + 2.7X10 “ M KTH74
HjCO-1" Reactions
12 + 12 9 1401 H2 CO + M - » M+ + H2 CO 2.6X10 “ PH80A 12 + + 9 1402 H2 CO + S ^ S + 1.0X10“ PH80A 12 + + 12 9 1403 H2 œ + sí » Si + H2 CO 1.0X10 “ PH80A 12 12 12 12 10 1404 h2 co++ c2- c2h^ + h co + h 8.2X10“ PH80A 12 + 13 l3 l2 10 1405 h2 co + c2 - ► C2H^ + H CO + H 8.2X10 “ =R(1404) 12 + 13 12 12 13 12 10 1406 h2 co + c c - C CH^ + H œ + H 8.2X10 “ = R(1404) 12 + 12 12 12 10 1407 h2 co + ch CH^ + H2 œ + 2H 3.1X10 “ PH80A;f2 12 + 13 13 12 10 1408 H2 œ + ch CH^ + H2 CO + 2H 3.1X10 “ =R(1407)
330
© American Astronomical Society • Provided by the NASA Astrophysics Data System o
TABLE 2— Continued Reaction Chemical Rate Parameters References, l_0 Number » Reaction A B C Status remarks a 12 12 + 10 1409 h2 co+ + NH ► H3 CO + N 6.4X10“ PH80A 12 12 h 12 12 10 1410 h2 co+ + c2 - c2h^ + h co 7.7X10 “ PH80A;f5 12 12 13 12 13 12 10 1411 h2 co++ c ch C CH^ + H œ 7.7X10“ =R(1410) 12 13 h 13 12 10 1412 h2 co+ + C2 c2h^ + h co 7.7X10“ =R(1410) 12 12 12 12 10 1413 h2 co+ + ch2- ch3+ + h2 co + h 4.3X10“ PH80A;f2 12 13 13 12 10 1414 h2 co+ + CH2- ch^ + h2 co + h 4.3X10“ =R(1413) 12 12 12 12 10 1415 h2 co+ + CH2- ^ ch^ + h co 4.3X10“ PH80A;f5 12 13 13 12 10 1416 h2 co+ + ch2 - - ch^ + h oo 4.3X10“ = R(1415) 12 12 12 + 12 9 1417 h2 co+ + h cn h2 cn + h co 1.4X10 “ M H77 13 13 + 12 9 1418 + h cn ^H2 CN +H œ 1.4X10 “ = R(1417) 12 + 12 12 12 9 1419 H2 œ + hn c — h2 cn+ + h co 1.4X10 “ = R(1417) 12 + 13 13 + 12 9 1420 h2 co + hn c ^h2 cn + h co 1.4X10 “ = R(1417) 12 + + 12 10 1421 h2 co + h2o — h3o + H œ 8.4X10“ PH80A 12 + 12 12 + 12 9 1422 H2 œ + h2 co ♦ h3 co + h co 1.0X10“ PH80A 12 + 13 13 + 12 9 1423 h2 co + h2 co ♦ h3 oo + h co 1.0X10“ = R(1422) ;f5 12 + 1/ 9 1424 H2 CO + NH, NH/ + H CO 1.1X10“ M H77 13 + + 13 9 1451 h2 co + M —► M + H2 CO 2.6X10 “ = R(1401) 13 + + 13 9 1452 H2 œ + 5 ♦ s + H2 œ 1.0X10 “ = R( 1402) 13 + + l3 1453 h2 co + si ^ si + H2 œ 1.0X10 =R(1403) 12 n + 13 1454 HPa)* + 2 ^ C-27H29 + H CO + H 8.2X10' = R(1404) 13 + I3 13 13 1455 h2 co + C2^ C2H2+ + H CO + H 8.2X10' = R( 1404) 13 13 12 12 13 13 1456 h2 co+ + c c c ch^ + h co + h 8.2X10' = R( 1404) 13 + 12 12 13 1457 h2 co + ch - CH/+ H2 CO + 2H 3.1X10' = R(1407) 13 + 13 13 + 13 1458 h2 co + ch - CH3 + H2 œ + 2H 3.1X10' = R(1407) 13 + 13 + 1459 h2 co + NH H3 CO + N 6.4X10' = R( 1409) ,3 + 12 2 13 1460 h2 co + c2h ' c2h+- h co 7.7X10' = R( 1410) 13 + 13 13 13 1461 h2 co + c2h c2h^ + h co 7.7X10' = R( 1410) 13 + 12 13 12 13 13 1462 h2 co + c ch c ch^ + h co 7.7X10' = R( 1410) 13 + 12 12 + 13 1463 H2 œ + ch2 - CH3 + H2 CO + H 4.3X10' = R( 1413) 13 13 H 13 + 13 1464 h2 co+ + C 2 “ - CH3 + H2 CO + H 4.3X10 = R(1413) 13 + 12 12 + 13 1465 h2 co + ch2 - ^ ch3 + H œ 4.3X10' = R( 1415) 13 + 13 13 13 1466 h2 co + ch2- - ch/ + h co 4.3X10' = R(1415) 13 + 12 12 + 13 1467 h2 co + h cn - h2 cn + H œ 1.4X10 = R( 1417) 13 + 13 13 + 13 9 1468 h2 co + h cn - h2 cn + h co 1.4X10 “ = R( 1417) 13 12 12 + 13 9 1469 h2 co+ + hn c -H2 CN + H œ 1.4X10 “ = R( 1417) 3 + 13 13 + 13 9 1470 Hj CO + hn c ^ h2 cn + h co 1.4X10 “ = R( 1417) 13 + + 13 10 1471 h2 co + h2o h3o + h co 8.4X10“ = R( 1421 ) 13 + 12 12 + 13 9 1472 h2 co + h2 co >h3 co + h oo 1.0X10 “ = R( 1422) ;f5 13 13 13 + 13 9 1473 h2 co+ + h2 co ^ h3 co + h co 1.0X10“ = R( 1422) 13 + I3 9 1474 h2 co + NH, ► NH/+ h co 1.1X10“ = R( 1424)
CHj' Reactions
12 + 12 12 + 1501 ch3 + c- c2h2 + H 5.0X10 0 PH80A 12 + 13 1502 ch3 + c- + H 5.0X10 0 = R(1501) ,2 + + 12 1503 CH3 + M -H M + CH3 2.0X10 ? PH80A 12 + 12 + 1504 ch3 + n - ► H2 CN + H 6.7X10 1 M F76 12 + 12 + 1505 ch3 + o h co + h2 4.4X10 0 M F76 12 + 12 + 1506 ch3 -i-s ► h cs + h. 1.4X10 ? PH80A 12 + 12 1507 CH3+ + Si Si + ch3 9.8X10 0 PH80A 12 + 12 1508 ch3 + h2 • CH5++ hi; 4.0X10 3 SA78; fl7 12 + 1509 ^3+ + NH -h2 cn + h2 7.5X10 0 PH80A 1510 ^H^ + NO —► NO+ + 12CH 9.5X10 0 M H77 12 + 12 + 1511 ch3 + o2- ► h co + h2o 4.3X10 1 M H77 12 12 1512 CH^ + OH -h2 co+ + h2 1.0X10 9 PH80A 13 + 12 12 13 1551 ch3 + c - C CH^ + H 5.0X10 0 = R(1501) 13 + 13 13 1552 ch3 + c - C2H^ + H 5.0X10 0 = R( 1502) 13 + 13 1553 CH3 + M - M++ CH, 2.0X10 -9 =R(1503) 331
© American Astronomical Society • Provided by the NASA Astrophysics Data System 1982ApJS. . .48. .32 IG Reaction Number 1681 1697 1696 1601 1692 1691 1682 1674 1673 1672 1671 1670 1669 1668 1667 1666 1665 1662 1661 1654 1653 1652 1648 1644 1643 1664 1663 1651 1650 1649 1647 1646 1645 1642 1610 1609 1608 1607 1606 1605 1604 1603 1602 1558 1557 1556 1555 1641 1611 1562 1561 1560 1559 1554 © American Astronomical Society •Provided by theNASA Astrophysics DataSystem 13 13+ 13+ 13+12 13+ 13+ 13+ 13+12 13+ 12+ 13+ 13+12 13 3+ 13 12+ 12 12+ 12+13 12+13 12+ +13 12+12 12+ 12+13 12+ 12+ 12+ + +13 + +12 +12 +13 13+12 12+ 12+ + +13 +12 1212+ + 1213+13 1213 13+ 1213 13+ 13+ 13+ 13+ 13+ l3 13+ 13+ hcn+ +nh- hcn +nh- hcn+ ch hcn+ ch hcn +nh- hcn +nh- hcn +ch hcn+ ch hcn+m- hcn +nh- hcn+ ch- hcn+ ch hcn++ ch h¡cn + HCN+ +M- hcn +nh- hcn+ +nh- hcn +nh- hcn+ ch hcn+ ch hcn+ ch ho+ ch- hcn +ch^hnc hcn - hcn+ ch- hcn+ CH- HCN+ CH- HCN+ M- ho +NH- ho +co- H0- H0 +HNC- ho +CH- ho+ C- CH+ CO- CH+ CO- HCN +M- ho- H0+CN- ho +HCN- H,0+ +C^HCOH, H3O+, HCN,CReactions cch +hco- cch^ +hco CH+ CO- CH^+ HCO- ch- CH +NOCH, ch- ch +h- ch +oh- CHf ch ch +o 23 23 2 2 2 2 2 2 2 23 2 2 2 2 23 2 2 2 2 2 32 23 2 2 2 2 2 3 32 3 3 32 3 2 2 2 3 3 3 2 2 2 2 2 3 3 3 32 3 3 3 'CH7 +N- 12 13 + Si— + s- hco - hnc- 2 NH 13+12 2 CH ^+HNCH +13 13+ 13+ 13+ 3 ch 13+ 13+ 13+ ^ Si+ch ► hcs+ ^ hco+ ^hcn +h 13+ 3 2 2 2 +12 »hco +h +I3 +13 +12 - hco+ *hco +ho 2 13+ -*hcn +h 2 2 12 12 12 12 -m +hcn » nh/+ho 2 2 13+ 12+ 13+ 13+ 12+ 12 ► M+HNCH ► m+hcn ^ M+HNC+H ch — nh^+hnc —► NHj"+HCN -^nh/ +hnc -^nh/ +hcn 5 13 13 NH 13+ - hco+o - hco+o - hcn+o ^ hcn+o - hcn+o * ch^+ho 12+ 32 32 2 2 2 2 13+13 1313 12+13 12+13 13+13 12+13 1313 12+13 13 ► nh/+hnc ► NH/+HCN ► +- ch +ho 13+12 13+ 12+13 13+12 12+ 32 12+12 hcn +o 13+12 12+12 ^ ch+hnc ^ ch/+hcn - ch+hnc ^ ch+hcn ► CH+HNCH • ch+hnch ► ch+hcn ► CH+HCN NHf+ HNC 2 3 3 3 3 3 3 3 12+12 13+12 ► ch+hnc ► hco+c ► hco+c ► hco+c ► hco+c ch +hnch CH+ HCN CH +HCN 3 32 32 32 32 13+1213 12+13 3 3 3 ch +hcn ch +hcn 3 3 - hco+cch -Hœ+ cch 3 3 + hv Chemical Reaction 13 hcn TABLE 2—Continued 332 10 10 n 10 13 10 -1 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 - 9.8X10“ 4.4X10“ 4.3X10 “ 7.5X10 “ 4.0X10 “ 9.5X10 “ 6.7X10 4.4X10 4.4X10 4.5X10“ 4.5X10“ 4.4X10“ 4.4X10 “ 4.4X10 “ 4.4X10“ 4.4X10“ 3.1X10 “ 3.1X10 4.1X10 “ 4.1X10 “ 4.1X10 ” 4.5X10“ 3.1X10 3.1X10 4.5X10 “ 4.4X10 “ 4.1X10“ 3.1X10 3.1X10 “ 3.1X10 4.1X10“ 4.1X10 “ 3.1X10“ 7.0X10 “ 7.0X10 “ 3.4X10 “ 2.2X10 “ 7.0X10 “ 7.0X10 “ 1.4X10 “ 3.4X10 “ 1.0X10“ 1.0X10 “ 1.0X10 “ 1.0X10“ 1.0X10“ 1.4X10 1.4X10 1.1X10“ 1.4X10 “ 1.1X10“ 1.4X10 “ 1.1X10“ 1.1X10 ï-9 -10 -10 -10 -10 -9 -9 -10 -10 -10 Rate Parameters B C Status M M PH80A PH80A PH80A PH80A PH80A; fl8 PH80A; fl8 H77 PH80A; fl8 =R(1511) =R(1510) =R(1509) = R(1605) = R(1512) = R(1508) = R(1507) = R(1505) = R(1643) = R(1641) = R(1605) = R(1605) = R(1603) = R(1601) H77 H77; fl8 PH80A; fl8 =R(1506) =R(1504) = R(1643) = R(1643) = R(1643) = R(1609) = R(1647) = R(1647) = R(1643) = R(1647) = R(1643) = R(1641) = R(1681) = R(1647) =R(1647) = R(1643) = R(1653) = R(1651) = R(1647) = R(1647) =R(1681) = R(1653) = R(1651) = R(1641) = R(1681) =R(1681) = R(1651) =R(1681) = R(1653) References, remarks 1982ApJS. . .48. .32 IG Reaction Number 2130 2129 2127 2128 2126 2125 2124 2123 2122 2119 2112 2109 2108 2107 2106 2105 2121 2120 2118 2117 2116 2115 2114 2113 2111 2110 2103 2102 2104 2101 1805 1804 1803 1802 1801 1851 1810 1809 1808 1807 1806 1857 1856 1855 1854 1853 1852 1860 1859 1858 © American Astronomical Society •Provided by theNASA Astrophysics DataSystem 12 1312 1312 13 12 12 12 13+ 12+ 12+ I2+ 12+ 12+ 12 13 13+ 13+ 13+ 13+ 13+ 13+ 12+ + 13 12 13+ 13+ 3121312 3113 3121213 31 3113 313 2112 1312 2112 212 212 212 3121213 3 3,3 313 2131213 21313,2 21 12 2,3 313 312i312 N+ c N+ CC- N+ CC- N+ c HCO+ +NH—NH^CO hco+ + hco+ + hco + hco + hco + hco + hco + hco + HCO+ + Neutral-Neutral Reactions hco+ + hco + hco + hco + hco + hco + hco + hco + HCO Reactions H +NCO H +NCO- HCX) +nh^nh/hco hco + 2 2 32 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 32 3 c +ncocn c +nco—cn c -i-ncocnœ c +nh—hnh c +hco->-I-ch c +oh—œh c +nco—cn 2c +hco^œ+ch c +hco^co+ch c +oh-^œh c +o^co C +NO^CON c +hco—ch C +O c +no->con C+ CH—c+H c +ncocn c +Nœ—cn+co CiFNH^HNC + 2c +NH—►CNH C+ CH C +NH—cnh C+ ch->C+H 2 2 0 2 2 12 + CH 13 13 12 1312 +12 1313 ,2 +13 1212+ 1313+ +13 12 12 13+12 12+ 13 12 NH, —NH^+Hœ NH. hnc- hnc- hcn Hor*"+co Si —+HCO hnc —hcn++co hnc Si ^+HCO hcn —+co 13 12 hcn —+co M ->+HCO hcn M —M++HCO ch ^+Hœ CH +HCO ch - ch — 2 2 2 2 2 2 2 2 2 32 32 3 12 13 12 cn+ c cn+ c co +o ♦ c-l-H >NH+ CO >NH+ CO 1312 1213 1312 2 cn+ c cn +c CC+ H 12 » nh/+Hœ 2 12+13 13 12+13 12+13 13+12 12+ -^hcn +hco 2 CH++ HCO+ ch+ hco »hcn +hco ► hcn+co ► hcn+co 32 32 2 2 2 Chemical Reaction TABLE 2—Continued 333 — 1 — 1 —10 -10 -12 -12 9 -12 9 9 9 9 9 -9 9 -9 9 -9 6.2X10 ° 6.2X10 6.2X10 ° 8.9X10 6.2X10 4.0X10 2.9X10 8.9X10“ 4.0X10 4.0X10 6.4X10 4.0X10 4.0X10 2.9X10“ 6.4X10 6.4X10 6.4X10 2.3X10 4.0X10 4.0X10 4.0X10 4.0X10 6.4X10 4.0X10 2.3X10 6.4X10 1.2X10 1.9X10 1.9X10 1.2X10 1.2X10 2.3X10 “ 1.2X10 1.5X10 1.2X10 1.2X10 2.3X10“ 1.5X10 1.0X10 ~ 1.0X10 “ 1.0X10 ~ 1.0X10 1.0X10 ~ 1.0X10 ~ 1.0X10 1.0X10 1.0X10' 1.0X10 1.0X10 “ 1.0X10 rt-12 ^ —10 -12 -12 -12 -9 -9 -10 Rate Parameters 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 B C Status M M M PH80A PH80A PH80A SK72 PH80A H77 PH80A 0.5*R(2112) PH80A = R(1803) 0.5*R(2112) PH80A B69 177 = R(1805) PH 80A PH80A B69 = R(1805) = R(1802) = R(1805) fl9 B75 = R(1805) = R(1803) = R(180O = R(1805) = R(1810) = R(1805) = R(1805) = R(1803) = R(2101) = R(1809) = R(2109) = R(2103) = R(2127) = R(2112) = R(2112) = R(2112) = R(2111) = R(2109) = R(2108) = 0.5*R(2127) = R(2109) = R(2107) = R(2106) = R(2105) = R(2103) = 0.5*R(2127) = R(2103) References, remarks 1982ApJS. . .48. .32 IG Reaction Number 2139 2138 2137 2135 2144 2142 2140 2136 2134 2133 2132 2131 2148 2143 2141 2156 2155 2153 2150 2149 2147 2146 2145 2164 2162 2160 2158 2157 2154 2151 2171 2169 2167 2166 2165 2163 2161 2159 2175 2173 2170 2168 2186 2184 2182 2181 2180 2179 2177 2176 2174 2172 2188 2187 2185 2183 2178 © American Astronomical Society •Provided by theNASA Astrophysics DataSystem 13 13 12 13 12 12 12 12 1313 1212 1313 1212 12 131212 131212 13 13 13 13 12 12 1212 121313 121313 13 12 12 12 12 13 1212 13 13 1313 1212 13 12 1313 13 13 13 12 1212 13 1313 12 I212 1313 n +co- N +NH—>H N+ CN—C+N N+ CN—C+N N +CH^CNH N+ CH—CN+H 0+ CH^CO+H o+ c—c+co n +co- n +hco^conh n +hco^conh N+ CH^HCN+ N+ CH-^HCN+H N +OH—►NOH N +NO—►O o+ cs^co+s o +cc—co+ o+ cc-^co+ o +c^co+ o+ ch O +OH—H O +NH—►OHN o +cs->cos o+ ch^cxm-h s+ ch^cs+h o+ ch o +hco^cooh o +cch—œ o +ch^œch o +ch^coch o +ch O +ch O +NO—>0N NO +NH—►NOH s +ch.- s +hco s +ch s +ch.S+CH—>HCS s+ ch^cs+h o +ch o +nco^cono o +nco^no O +NH—OH o +hcs— o +hcs^ocs o +hco—œOH S+ ch—hcs+h s +hco- NO +NH,—»N,H,0 Hœ- Hœ +OH 2 2 2 CS +OH—0h 2 2 2 2 ch +OH- cn +o-^nco 2 ch +OH- cn +o^nco CS +OH-»0H 2 0 3 2 2 2 2 2 2 3 2 32 2 2 2 2 2 2 OH 12 13 12 1J 13 12 13 12 l3 12 > Hcs+ ^0CS +H ^0CS +H ► HCS+ ♦ hco+ *hco- 12 2 ► CO+H > CO+H 2 2 13 12 13 12 »n+ œ ♦ n+œ 2 2 œ+ CH -^HCX) +ho -*hco +ho ► HCO+ ► Hœ+h 2 2 2 2 Chemical Reaction H TABLE 2—Continued 334 3.0X10" 4.1X10" 4.0X10“ 4.0X10" 8.7X10' 3.0X10" 4.0X10“ 4.0X10' 8.2X10' 4.0X10“ 4.0X10“ 4.0X10' 2.9X10" 2.9X10' 2.3X10' 4.0X10' 8.7X10' 2.0X10' 4.0X10“ 2.9X10' 1.0X10' 1.2X10“ 4.0X10“ 2.9X10" 4.0X10“ 6.9X10“ 2.3X10" 2.6X10' 2.3X10" 4.0X10" 1.0X10" 1.0X10' 5.0X10" 6.9X10“ 1.6X10' 1.2X10“ 2.9X10" 5.0X10" 1.0X10' 2.6X10' 2.3X10“ 4.0X10" 1.2X10' 2.9X10" 2.9X10' 1.0X10“ 5.0X10" 1.2X10' 1.2X10" 1.0X10“ 5.0X10" 1.0X10' 2.9X10' 1.2X10' 1.0X10“ 1.5X10" 1.5X10“ Rate Parameters 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 B C 250. PH80A 750. MCG74;PH80A 250. Hd77;PH80A 200. PH80A 250. 0.5*R(2158) 250. =R(2185) 250. 0.5*R(2158) 250. =R(2158) 250. =R(2187) 750. =R(2150) 410. MCM75;PH80A 200. =R(2167) 250. PH80A Status M BT68;PH80A M =R(2169) M T67;PH80A M WdH72;WMB74;PH80A M G74;PH80A M BT67;f6 SPG74;PH80A OD74A This work;f22 PH80A HG77;PH80A HG77;PH80A This work;f21 This work;f21 W72;Hd77;PH80A This paper PH80A; f20 PH80A PH80A IS78 177 PH80A PH 80A PH80A PH80A PH80A = R(2181) = R(2171) =R(2179) =R(2173) =R(2138) =R(2177) = R(2175) = R(2162) = R(2156) = R(2140) = R(2164) = R(2148) =0.5*R(2144) = R(2142) =0.5*R(2144) = R(2144) =R(2133) =R(2131) References, remarks 1982ApJS. . .48. .32 IG 2202 2203 2201 2205 2204 2210 2206 2212 2211 2209 2207 2214 Reaction 2215 2213 2216 2218 2217 2220 2219 2282 2281 2222 2221 2228 2227 2226 2224 2223 2230 2229 2225 Number 2231 2235 2234 2233 2232 2240 2238 2237 2236 2245 2244 2243 2241 2239 2249 2248 2247 2246 2242 2250 2253 2252 2251 © American Astronomical Society •Provided by theNASA Astrophysics DataSystem +- - + 1— — +— +_ — +- + 13+- 12- + + +- 12t-12 12 +- 13+—13 12+_12 13+_13 13+_ 12+ 1312+ 13+ 1312+_ 12 1312_ 12 13_ 12- 13+_ 13 12+_ 12+_ 12 ,212 12+_ 13+13 12-12 ,3+_13 13+ 13+_ 13+- 12+ 2+l2 1212 13+_ 12+ 13+_ i2 1213 1213_ 13 13 Eletron-Ioo Recombination S +e—♦hv Si++ e—»Si+hi/ 0 +e~^O+hv N"' +e—»Nhp He"*~ +e—»Hehy H +e—►hr SH+e —»SH O2" +e—>O NO +e—♦NO M++e~ —M+hy H, +e~—>H C +e^C+hp C+ +e^h* 0H+ e~ NH +e~ H0 +e HCO"" +e—CO CN++ e“-c H30+ e HCS+ e—CS+ HCS +e— HCO+e — CN+ e^- CN+e“ CCN +e“^N CN +e“ CCN +e CCN+ +eCN HCS+ +e^HCS HCS+ +e—CS HCN+ e■ HCN+ +e~■ HCN +e■ HCN +e• CH++ e“ CH^+ e~^CH CH +e HCS+ e“—CS+2H HCS++ e—CS+2H CH +e—H HCX)+e“ HCX)+ e HCO +e HCO+e~ HjCO +e~^2H HCO+ -fe“—CO+ CH4-e 2 CH+ e~ CH4-e ch+ CCH^ +e" CCH^ +e CH^ +e" 2 ch 2 3 2 2 2 2 2 2 2 2 3 2 3 32 2 2 2 2 2 3 2 3 2 2 2 + e T e 12 > OH+H ^ H04- ► 0+H ♦ N+H 13 13 12 12 2 2 2 2 12 13 13 • CH,+hv - c+2H - ch+ - c+2H ^ CH+ 13 13 13 12 12 13 2 2 2 2 CH +H CH +hl/ ch +H 1312 1213 13 13 12 12 ♦ HCO+hi; » œ+2H >HCO +H /HCO+ hv 3 2 CN +C cn+ c 2 2 - C+2H - CCH+H HNC +H HCN + HCN + HNC+ H + N + H Chemical Reaction N 2 TABLE 2—Continued 335 9 6 -6 6 6 6 6 6 6 6 6 6 6 6 6 6 9 6 6 6 6 6 9 6 6 6 6 10 6 -10 6 10 -10 6 -10 -10 5 6 -10 -10 5 6 10 5 6 6.1X10 “ 8.8X10 “ 1 7X10 5.2X10 “ 5.2X10 “ 5.2X10 “ 1.7X10 “ 5.2X10 “ 5.2X10 “ 5.2X10 “ 5.0X10 “ 5.2X10 “ 5.2X10 “ 5.0X10 “ 5.0X10 “ 5.0X10 “ 6.1X10 “ 5.0X10 “ 6.5X10 “ 6.5X10 “ 6.5X10 “ 5.0X10 “ 6.1X10 “ 6.5X10 “ 5.5X10 “ 5.2X10 “ 5.5X10 “ 2.6X10 1.9X10“ 5.2X10“ 2.6X10 1.9X10 2.6X10' 2.6X10 “ 1.9X10“ 1.9X10 5.2X10“ 2.6X10' 1.9X10 1.9X10 1.5X10“ 5.7X10" 3.2X10" 4.0X10“ 1.9X10 1.9X10 1.4X10“ 3.5X10“ 1.3X10“ 1.9X10“ 1.4X10“ 1.3X10“ -6 -6 -6 ■6 -6 -6 -6 Rate Parameters -0.7 -0.5 -0.5 -0.7 -0.5 -0.5 -0.5 -0.5 -0.5 -0.5 -0.5 -0.5 -0.5 -0.5 -0.5 -0.5 -0.5 -0.5' -0.5 -0.5 -0.5 -0.7 -0.5 -0.5 -0.7 -0.5 -0.5 -0.5 -0.5 -0.5 -0.5 -0.5 -0.8 -0.8 -0.5 -0.5 -0.5 -0.5 -0.5 -0.5 -0.5 -0.5 -0.5 -0.5 -0.5 -0.7 -0.7 -0.7 -0.7 -0.7 -0.7 -0.7 -0.7 -0.7 B C Status M MM79B M LBJ73B;PH80A M f6;f24 M MM79A M MM79A SK72;BDO75;PH80A PH80A PH 80A = R(2250) PH80A;f8 = R(2249) = R(2248) = R(2245) PH80A;f8 = R(2244) fl8 fl8 SK72;BDO75;PH80A = R(2241) MM80; H = R(2240) MM80; f7 = R(2235) = R(2234) = R(2235) M79 = R(2234) PH80A = R(2230) = R(2229) = R(2228) M79 MM79B MM79B PH80A PH80A PH 80A PH80A = R(2281) = R(2222) = 0.5*R(2216) =0.5*R(2216) = R(2215) BD77 BD77 = R(2216) = R(2215) BD77 BD77 BD77 BD77 BD77 BD77 = R(2203) References, remarks 1982ApJS. . .48. .32 IG + 13 16 + 3-1 15 -5 173 163- The rateconstantforthisreactionisassignedbyconsideringthe ionization rateisfromGUIA,adjustedforthemorerecentbranch- cosmic-ray ionization./5:Thisreactionisassumedtoproceed ing ratiogivenbyCD78forprimaryproductionofHand reaction tobelimitedbythechargeexchangestep./3:Weassume be muchsmaller.fl2:Thereactionrateconstantforradiative constant forformationofHbycatalysisongrainsissimilar nels hasbeenassignedinthiswork.flO:Thevalueoftherate reaction isbasedonMM80andassumesanequalbranchingratio arise fromtheonlychannelavailabletoreactants./7:This The endothermicityofthisreactionhasbeenestimatedfroma will bemuchloweratthetemperaturesofourcalculations.fl5\ measured byFehsenfeld1979at100K.Iftheactivationenergy that theC-Obondisnotbrokeninthisreaction.f4:Thetotal lation tolowenergiesofarate constantbasedonacollisional ions («4X10“cms”PH80A);thisrateconstantisstilllarge comparison oftheforward(reaction1320)andreverseratecon- estimated byPH80A,LE/k—1044K,iscorrect,therateconstant HIT). fl4:Thereactionrateconstantusedhereisthevalue major constituentsofthemetals,M)tobreakH-CObond(cf. cient energyremainsafterchargeexchangewithMgorFe(the diffuse cloudsisconsistentwithavalueintherange10“(Langer son ofpredictedandmeasuredvaluestheCHabundancein cule reactionsindenseclouds,isunknown;estimatesrangingfrom association ofCwithH,onethemostimportantion-mole- formation indiffuseclouds,fll:Therearenoexperimentaldata to thatsuggestedbythestudyFedermanetal.1979ofH the twochannels.f9:Thebranchingratioforalternatechan- for thetwochannels.f8:Anequalbranchingratioisassumed through protontransfer.f6:Theproductsshownareassumedto CH inclouds,sincethedetection reportedbyFoxandJennings cm s).Theprecisevalueisimportant forcalculatingthemethane much smallerrateconstantmay apply (PH80Ausek=1X10~ radiative associationofCHjisSmith andAdams’s1978extrapo- as isthecaseforallregimesofinteresthere,fl7:Thisvalue enough tojustifytheuseofanabbreviatedreactionifx(e)<10 , Dalgamo 1977).fl3:Thisreactionmaybeincorrectsinceinsuffi- for thisreaction(seeAlbritton1978),anditsrateconstantmight abundance ininterstellarclouds. Presently thereisnoevidencefor association process.Green1981 hascriticizedthisapproach;a tion, CH4,reactsmoreslowlywithHthandomostmolecular stant measuredat300K.//<5:Theintermediateioninthisreac- 1978 hasbeenshown byEllderetal.1980tobe attributableto 10“ tocms~canbefoundintheliterature.Acompari- 1978), thevalueadoptedhere,to6X10“cms(Blackand 2 2 2 4 2 Notes.—fl: Thisreactioncombinestwopossiblechannels./2: © American Astronomical Society •Provided by theNASA Astrophysics DataSystem Reaction Number 2268 2266 2265 2264 2263 2262 2259 2257 2256 2286 2284 2260 2258 2255 2254 2285 2283 2267 2261 - 12+ 13 12 12+ 13+ 13+-13 13+ 12+ 12+ 13+ 13- 12+ 12+ 13+- NH NH NH3" +e^ NH HCO+ e“ NH H0CS++e H0CS+ +e H0CS+ e Hœ +e" HCO +e HCO +e" HCO +e" HCX)+ e H0CS +e CHf +e^CHH CH +e“^H CH +e~■ CH +e^H 3 3 32 3 3 3 2 52 5 532 + 3+e- 3 + . '+ e~ + e~ + e 12 12 12 ^ NH+H ♦ nh+h " —Hœ+ - HCO+ ► NH+hv ► NH+H ► NH+H - ^CS+OH 3 2 2 3 2 2 12 13 12 ch +h I3 ► Hœ+h ► œ+H 32 2 2 13 12 13 CO +H 2 ocs +h ocs +h cs +oh Chemical Reaction TABLE 2—Continued -9+ + + + _6 —9 —6 6 -6 isomers HCNandHNCwithequalprobability,sincethelinear bond isnotbroken.ß3:Therateconstantsetbyanalogywith Thrush 1967.BT68:Bodenand1968.BD77:Black major destructionpathforOH,thisshouldnotintroducesignifi- performed with£=8.2X10.SincereactionHisnota of thehydrogenatomstoformHCNandthatrearrangement rearrangement toformHCN(themorestableisomer)doesnot replaces oneofthehydrogenatomstoformHNCandthat (see Liddyetal.1977).fl9:Itisassumedthatthecarbonatom CHCOOH. fl8:DestructionofHCNisassumedtoformthe WAH76: Watson etal.1976. cant error. quoted hereisfor10K.ß6:Ourcalculationswereinadvertently reaction hasacomplicatedtemperaturedependence;thevalue energy tobreakeithertheC-0orC-Sbond./22:Itisassumedthat replaces thehydrogenatomandthatthereisinsufficientremaining form HNCdoesnotoccur,ßl:Itisassumedthatthesulfuratom form ofthision,HCNH,appearstobethemoststablestructure Westenberg anddeHaas1972. WMB74: Washidaetal.1974. MM80: MulandMcGowan1980. OD74A:Oppenheimerand LH74: LaudenslagerandHuntress1974.LBJ73A:Leuetal.1973a. etal. 1980.KH75A:KimandHuntress1975.KTH74: 177: Iglesias1977.IS78:andSilk1978.JCB80:Johnsen HG77: HampsonandGarvin1977.HKT74:Huntressera/.1974. Herbst era/.1975.H77:Huntress1977.Hd77:Hudson G73: Gehringetal.1973.GL74:GlassgoldandLanger1974.H75: FS71: FieldandSteigman1971.FF73:FehsenfeldFerguson F73: Ferguson1973.F76:Fehsenfeld1976.F79:1979. Dalgamo 1977.BD075:Blacketal.1975.CG74:CupittandGlass the averageofvaluesmeasuredbyLBJ73AandM79.ß5\This the sulfuratomreplaceshydrogenandthatremaining take place.ß0:Itisassumedthatthenitrogenatomreplacesone etal. 1974.V80:Viggiano1980. W72:Wilson1972.WdH72: Dalgamo 1974a.PH80A:Prasad andHuntress1980a.R72: Mul andMcGowan1979a.MM79B:19796. LBJ73B: Leuetal.19736.M79;McGowan1979.MM79A: the reactionofNHwithCO.ß4:Therateconstantusedhereis Schiff andBohme1979.SPG74: Slagleetal.1974.T67:Tunder Smith andAdams1978.SA80: Smith andAdams1980.SB79: Rutherford etal.1972.SK72:Solomon andKlemperer1972.SA78: 1973. FGK79:Federmanetal.1979.G66:Goldan1966. 1974. CM75:ClyneandMcDermid1975.D68:Dunkinetal.1968. 1979. B69:Braunetal.1969.B75:Black1975.BT67:Brownand 1974. KTH75A:Kimetal.1975a.KTH75B:etal,\915b. 215 32 2 6.0X10“ 6.0X10“ 6.0X10 6.0X10 2.0X10 9.5X10 9.5X10 6.1X10 5.2X10 5.2X10 3.5X10 1.0X10 ~ 1.0X10 3.5X10 3.5X10 1.0X10“ 1.0X10“ 3.5X10 1.0X10“ References—AHF76: Anicichetal.1976.A79:Albritton -6 -6 -6 -6 -7 -7 -6 -6 -6 Rate Parameters -0.5 -0.5 -0.5 -0.5 -0.5 -0.5 -0.5 -0.5 -0.5 -0.5 -0.5 -0.5 -0.7 -0.5 -0.5 -0.5 -0.5 -0.5 -0.5 B C Status M SK72;PH80A PH80A PH80A PH80A; f8 PH 80A PH80A PH80A; f8 PH80A PH 80A PH80A M79 = R(2266) = R(2265) = R(2284) =R(2283) = R(2258) =R(2257) = R(2265Ï = R(2259) References, remarks 1982ApJS. . .48. .32 IG 1318 12 1216 6 3 -193 -103 isotope. Forallunmeasuredexothermicreactionsinvolv- ing theC(0)isotope totalrateconstantistaken equal tothatofthecorresponding reactionforC for reactionsinvolvingcarbon(oxygen)bearingspecies tions discussedin§Ilcviiibelow),fortheC(0) are, withtwoexceptions(theisotopefractionationreac- number densityofspeciesX. breviated reaction1304isthereforetakentobethatof plifies thecalculationbyomittingfasteststepsand initial reaction(1304a).Therateconstantfortheab- less than0.1yr,ascomparedwithatleast10yrforthe The reactionrateconstantisindicatednexttothe behavior ofthetotalsystemevenifsomeatomichydro- reducing thenumberofequationssolved.Theabbrevi- reaction (Fehsenfeld1976for1304aandHuntress1977 but omitsspecifictreatmentofHmoleculesdestroyed. keeps explicitcountofthenumberHatomsproduced here. well ifHcomprisesmorethan20%ofthegas,a for 1304b,1304c).Thecharacteristictimescalesunder calculation canthusbesimplifiedwithouttheintroduc- condition n=n(H)+2n(H)27>i(^lH,thetotal H, itdoessolessrapidlythanreactswithH.(Typi- gen ispresent.Ingeneral,ifamolecularionreactswith is representedinourreactionschemeas condition satisfiedfortheregionsunderconsideration cally, thisdifferenceisafactorof~5;e.g.,N^+Hhas ated reactionschemeisagoodapproximationofthe the slowestrateinchain.Thisprocedurethussim- the conditionsconsideredhereforreactionswithHare tion oferrorsinthehydrogenabundance. Since thelattercanbecalculatedfromconservation for N^+H.)Therefore,theabbreviatedschemeworks s, comparedwithk=1.7X10cmmolecule a reactionrateconstantof1.9X10cmmolecule 2 2 tot2/7 2 2 2 3 Existing measurementsorestimatesofrateconstants Throughoutthispaperthenotation «(X)referstotheabsolute Our treatmentoftheseabbreviatedreactionschemes © American Astronomical Society •Provided by theNASA Astrophysics DataSystem iii) RateParametersforCarbonandOxygenIsotopes + OHj +H->H0+H, 23 OH+ +H^OHj+H, 2 + 103- -931 4-0^H0 +H+H+H, 32 6.1 X10“cmmolecules,(1304c) 1.1 X10cmmolecules,(1304b) -103 8X 10cmmolecules.(1304) DENSE INTERSTELLARCLOUDCHEMISTRY 1618 1213 1213 16 ple, thereactionsofcarbonionswithHCNare included allpossibleisotopecombinations.Forexam- the isotopesandderiveacorrectisotoperatio,wehave between speciescontainingbothcarbonandoxygen reactions for0/Oprocesses,northecross-reactions Table 2,whichincludesthereactionsnecessarytodis- The isotopicfeaturesofthechemistryareindicatedin initiate nitrogenchemistryinearliermodelcalculations of brevity,wehavenotpresentedheretheanalogous larger numberofpossiblefinalproductswhichcan Kuntz, 1978)becausethere is noevidenceforreactions (Herbst andKlemperer1973;Mitchell,Ginsburg, tinguish betweenCandprocesses.Intheinterest Huntress (1977)hascriticizedtheuseofthisreactionto atoms. result whenbothisotopesareinvolved.Forexample, two channelsarenecessaryforanyreactionofC, (0). Properaccountmustbetaken,however,ofthe as with portant, weindicateitasshown here. Ifnoisotopedesignationis channel is of carbonandoxygenbecausetheonlyexothermic needed, wehavefollowedthestandard conventionofomittingthe superscript forthemostabundant oftheisotopes. The reactionrateconstantforeachbranchhasbeen one isotope, taken tobehalfthatforthecorrespondingreaction 4 In ordertoconserveproperlythenumberdensityof The chemistryofH^withnitrogendiffersfromthat Wheredesignationofthecarbon oroxygenisotopeisim- 12+12 13+123 12+132 13+13 c +hn^n+h, c +hn-*n+h. c +hn->n+h, c +hn^n+h, 2 2 12132 c+o^ I313, l212 c+o^o+. c+o^o+, 2 2 H+ +N^NHj+H. iv) NitrogenChemistry 13124 ^CO +. 337 1982ApJS. . .48. .32 IG 9 3-1 + + + include thisreactionandassumearateconstant10~ of thistypeinwhichanHjionistransferred.The we havechosentoconsideronlydirectionizationof models ofPrasadandHuntress(1980a),nonetheless,do cm molecules.Inthecalculationsdescribedherein, nitrogen bycosmicraystoinitiatethenitrogen-hydro- has beendeterminedintermsoftheprimarycosmic-ray reaction, gen chemistry(e.g.,NH,NH,).Therateforthe 338 Another featureofthenitrogenchemistryininterstellar ionization rateofatomichydrogen,Ç,scaledforthe There areseveralreactionswhichproduceHCNand clouds isthepresenceofHNC,isomerHCN. ion-molecule chemistry;seeLiddy,Freeman,and has alinearstructure(notethatitispossibleother presumably nearunity,sinceitisassumedthatHCN produces bothspecies.Thebranchingratioofthesetwo reacts rapidlywithHand,inaseriesofreactions different crosssections(Langer1978).Thenitrogenion channels (reactions2240and2241)isunknownbut HNC. Forexample,recombinationofHCN, with radicals;e.g., volved intheirformation.Forexample, H, formsNH^“(seereaction603inTable2). reaction forcarbon, McEwan 1977;Allen,Goddard,andSchaefer,1980). structures ofHCNexistandcouldbeformedinthe chemistry byreactingwithothermolecularionsand (reaction 2138),onlyformsHCN,whiletheanalogous another islikelywhenneutral-neutralreactionsarein- Selective formationofoneisomerinpreferenceto oxygen inthateventhough the reaction during thereaction. (reaction 2111),shouldonlyformHNC(unlessre- 23 arrangement occurs)sinceonlyanHbondisreplaced p 2 2 2 2 2 Atomic nitrogencanalsoenterintothegasphase The sulfurchemistrydiffers fromthatofcarbonand © American Astronomical Society •Provided by theNASA Astrophysics DataSystem + + + CH^+N^HCN+H, HCNH +e^HCN+H 2 CR+N N+e+CR, + CH+N^CN +H. NH+C^HNC+H CH+N^HCN 2 2 H^ +S-*SH+H 2 v) SulfurChemistry ^HNC +H, GRAEDEL, LANGER,ANDFRERKING + + + + + is exothermic,thesubsequentreactionofSHwithH is not.OppenheimerandDalgamo(1974a)suggested but, followingtheapproachadoptedfornitrogen while avoidingtheuncertaintiesofmolecularsilicon interaction ofsiliconwiththecarbonandnitrogencycles not includethisreaction.Inourchemicalformulation, the useofexothermicreaction ion-molecule chemistryapplies.Forthisreason,aswell (1977) ontheunlikelihoodofHiontransfer,wedo chemistry andinaccordwiththecommentbyHuntress chemistry. charge transfertometalswithlowerionizationpoten- only ionizationbychargeexchange(e.g.,reaction302) regions ofinterstellarcloudswherethegasphase in theirreactionsthedenseregionsofinterstellar herein. have omittedthatprocessfromthecalculationsreported in contrasttothoseofearliermodels,includedapos- carbon ornitrogen. our sulfurchemistrytoagreaterextentthanthatof and withradicals,althoughwehavechosentorestrict silicon oxideprocesses.Suchanapproachpreservesthe tials (seeLanger1976).Weneglectsiliconhydrideor and neutralizationbyrecombinationwithelectronsor as currentuncertaintiesinsiliconchemistry,weinclude Hartquist 1978),itisuncertainwhetherSiOpresentin chemistry isthoughttooccur(Lada,Oppenheimer,and clouds. AlthoughSiOisdetectedinregionswhereshock sulfur formsmoleculesbyreactingwithmolecularions and Dalgamo1977),yetsignificantdifferencesexist dant ininterstellarclouds.Theevidencethusdoesnot Linke 1981)indicatesthatHCSisreasonablyabun- Recent observationalevidence(Thaddeus,Guélin,and consequence ofthisreactionistherapiddestruction, appear tofavorthereactionofHCSwithH,andwe and hencethelowcalculatedabundance,ofHCS. tulated reactionofHwithHCStoformCS.A 2 process ofradiativerecombination, sincethemetalions 2 by chargeexchangeprocessesoftheform, do notreadilyreactwithmolecules. Theroleofnega- (reaction 1303)andareneutralized bytherelativelyslow ular cloudswaspointedoutbyOppenheimerand tively chargedgrainsinneutralizing metalionsispoten- Dalgamo (1974a).Metalatomsareionizedprincipally 2 2 The calculationsofPrasadandHuntress(1980a,h), Silicon ischemicallysimilartocarbon(e.g.,Turner The importanceofmetalstotheionbalanceinmolec- + h^+m^m+h, 2 H^" +S->SH+H, 2 vi) SiliconChemistry vii) MetalsChemistry Vol. 48 1982ApJS. . .48. .32 IG -7 -103 -1 + 5 + + 103- -103 larger thanthatofradiativerecombinationwhenx(e)< perature of10Ktheneutralizationrateongrainsis 2X10 (Elmegreen1979;UmebayashiandNakano radiative recombinationwithfreeelectrons.Atatem- tially importantsinceitcancompeteeffectivelywith dance ofspeciesrelativetothat ofH;i.e.,the“relativeabun- values usedinourcalculations incorporatethistempera- lower temperaturestheforwardrateconstantswillbe proton exchangereactionSmithandAdams(1980)de- with decreasingtemperature.At80Ktheydeterminea be importantistheprotontransferreactionbetween No. 3,1982 dance.” LE/k =\4±5K(ingoodagreementwiththeestimate isotope exchangereactionwillbeevenmoreimportant measured byWatson,Anicich,andHuntress(1976)at rate constantof6.8X10cmmoleculesforthe was firstconsideredbyWatson,Anicich,andHuntress reverse valuesisconstant(Smith andAdams1980).The of 17KGuélin,Langer,andWilson,1982).Ateven cule sat80Kandfromthereverserateavaluefor room temperature.Theirmeasurementsindicatethatthe carbon isotopicexchangereaction,3timesthevalue HCO, COreactionsoveratemperaturerangeof80- and oxygenisotopeswitchingby reaction (1976) whoalsomeasuredtherateconstantfor 1980). and reverserateconstantsofboththeC,CO switching isaccomphshedby HCO andCO(Langeretal.1978).Carbonisotope temperature giventheuncertaintyofmeasurements. to measureanydifferenceinthesetworatesatroom to Watsonetal.LE/k=?>5K,anditwasnotpossible K forboththeforwardandreverseprocess.According and found(2±0.2)X10“cmmoleculesat300 somewhat largersincethesumofforwardand termine aforwardrateconstantof4.2X10cmmole- than hasalreadybeensuggested(Langer1977).Forthe 500 Kandfindanincreaseintheforwardrateconstant (other isotopiccombinationsareobviouslypossible). 2 5 Another isotopicenhancementreactionwhichcould Throughoutthispaperthenotation jc[X]referstotheabun- Isotopic fractionationofcarboninmonoxide Smith andAdams(1980)havemeasuredtheforward © American Astronomical Society •Provided by theNASA Astrophysics DataSystem 12+l3 16+8 HCO +O
+ Fig. 3.—Relative carbon pool abundances as functions of cloud age and cloud density for C and CO. The fraction n(C )/n(Ctot) is less than 0.02 throughout the density-time regime displayed here. For the large electron abundance appropriate to the high metal abundance model, the conversion from atomic carbon to molecular CO is complete only for densities greater than 1048 cm-3. At lower densities, substantial amounts of atomic carbon are still present. A lower electron abundance, as in the low metal abundance model, results in complete conversion of C into CO at lower densities.
344
© American Astronomical Society • Provided by the NASA Astrophysics Data System 1982ApJS. . .48. .32 IG 8 (1) moleculesthathavebeenobservedindenseinterstellarcloudsareindicatedbycross-hatching;thosewhoselifetimesextremely short contribute >5%ofthetotalformationordestructionratemoleculeareindicated.(3)Solidarrowsindicatedominant source or relative tothetimescalesofinterestareinboxeswithdottedoutline.(2)Onlyreactionswhichatsomechemicalevolution more thanonereactionhasbeenrepresentedbyasingleline,thedominantreactantiscircled.(4)Insomeinstancescontributes sink forthemoleculeatendoftime-dependentcalculation(10yr).Iftworeactionsareequallydominant,bothindicated. Where situation anarrowappearsonlynearthespeciestowhichreactionmakesa>5%contribution. >5% oftheformationrateforamoleculebutdoesnotcausetotaldestructionitsprecursor,orviceversa. Inthis Fig. 4.—ChemicalreactionflowdiagramfortheC„H„family.Thefollowingconventionsareusedonthisandsubsequentdiagrams: © American Astronomical Society •Provided by theNASA Astrophysics DataSystem 3 2 3 4 3 4 3 2 3 5 4 3 5 4 2.5X10 5.0X10 2.5X10 2.5 X10 5.0X10 2.5X10 5.0X10 5.0X10 1.0X10 1.0X10 1.0X10 1.0X10 1.0X10 1.0X10 3 (cm ) n(H) 2 4.4(—9) 6.0(—8) 4.6(—11) 2.0(—10) 6.1(—10) 9.1(-5) 5.5(-5) U(-4) 1.2(-4) 1.4(—4) 1.6(-9) 1.9(-8) 1.2(-8) 1.3(-4) .x(C) 8 Fractional AbundancesoftheCarbonFamilyat10Years 2.8(—9) 3.5(—10) 4-5(—9) 2.1(-11) 6.6(—11) 2.9(—9) 6.9(-9) 3.7(—12) l.l(-9) l.l(-8) 1.7(-8) 1.5(—10) l.l(-ll) 1.5(-9) jc(CH) High Metals Low Metals TABLES 2.6(-9) 4.2(-9) 2.2(—8) 3.1(-11) 2.7( —10) 5.2( —10) 5.5(-9) 9.6(-9) 3.2( —8) 3.9(—8) l.l(-lO) 1.0( —9) 1.5(-11) 1.5(-8) x(CH) 2 345 4.6(—11) 6.2(—11) 6.4(—12) 2.9(—10) 8.5(—13) 7.4( —11) 9.0( —11) 9.9( —11) 3.4(—11) 5.4( —11) 8.7(— 11) 8.4( —11) l-8( —11) 1.7(—10) jc(CH) 3 4.8( —10) 4.1(-9) 5-3( —9) 9.5(-9) 2.1(-8) 2.5(-8) 2.7( —8) 9.1(—12) 3.7(—11) 9.7( —11) 2.1(—10) 1.5(-8) l.l(-ll) 1.6(-9) x(CH) 2 4.1(-9) 4.1(-8) 2.1(—10) 2-5(—9) 7.2(—13) 7.9(—9) 2.7( —8) 3.4( —12) 3.4(—11) 8.0(— 11) 8.5(—10) 1.2(-11) 1.5(-9) 1.4(-8) *(C) 2 (HIGH METAL ABUNDANCE) (HIGH METAL ABUNDANCE)
Fig. 5.—Relative abundances of selected C„H„ species as functions of cloud age and density. The time dependence of n(CH) is very similar to that of n(C) because the hydrogenation of C by (shown in Fig. 4) proceeds rapidly. The C2H abundance initially lags behind that of CH in the high metal abundance calculation because its formation requires additional chemical reactions, but after ~ 106 yr it also mimics n(C). At low electron abundance and long times, h(C+ ) is an important factor in the chemistry of these species. Shown in this figure + are C, C , CH, and C2H.
346
© American Astronomical Society • Provided by the NASA Astrophysics Data System 1982ApJS. . .48. .32 IG © American Astronomical Society •Provided by theNASA Astrophysics DataSystem (HIGH METALABUNDANCE) CH Fig. 5.—Continued 347 (HIGH METALABUNDANCE) ch 2 1982ApJS. . .48. .32 IG + + + 348 jc(H^)/x(He)>l, analogoustothesituationfor whereas HCOiscoupledtotheC„H„species(seeFig.4caption The observablespeciesHCOisverystronglycoupledtoCO, ions thanareOH,H0,and0. for explanationofsymbols). This differenceoccursbecauseCOisdestroyedbyfewer cant fractionofcarbonisinCO(~10%),whereasonly carbon inwhichnearlyallCisconvertedintoCO.Some oxygen istransformedinto0andHonlywhen are giveninTable7;alsoincludedforcomparison differences ariseifx(H^)/x(He)
High Metals + H2CN +£^HCN+H. 5.0X102 8.2(—12) 2.9(—10) 1.0X103 9.1( —12) 4.3(—10) The abundances of CN and HCN are closely linked to 2.5X103 l-l(-H) 7.1(—10) 3 the abundances and evolution of CH and CH2, respec- 5.0X10 l-l(-H) 1.3( —9) tively, as can be seen in Tables 5 and 8 and Figures 5 1.0X104 1.2( — 11) 3.0(-9) 2.5X104 1.7(— 11) 6.0( — 9) and 11. At low electron abundance, for example, the 1.0X105 7.3(—11) 1.5( —9) HCN and CN fractional abundances peak at inter- mediate times (~fewX106 yr) and then decrease sig- nificantly as carbon (a source of CH and CH2) is model calculations because the reaction of with N is converted into CO. At long times the primary source of assumed not to take place. Instead, atomic nitrogen is HCN differs in different cases. In the high metal case ionized by cosmic-ray protons, and the reaction of the (for all densities), the neutral-neutral reaction CH2+N resulting ion with H2 initiates the production of the is the primary production process. For the low electron + 3 -3 nitrogen-hydrogen molecules NH*, N2, and N2H . As abundances and h(H2)>;2X10 cm , the recombina- + discussed below, our calculations fail to reproduce the tion reaction H2CN + e is the primary HCN producer. + observed abundances of NH3 and N2H , the only The contributions of these two channels keep x(HCN)
Fig. 8.—Chemical flow diagram for the 0„H„ family. The hydrogenation of the oxygen family proceeds rapidly by means of the reactions of H J with O (see Fig. 4 caption for explanation of symbols).
© American Astronomical Society • Provided by the NASA Astrophysics Data System 1982ApJS. . .48. .32 IG 4-3 both carbonandsulfurconsistsinourmodelprimarily with CH(reaction2171),andOCSisproducedfromthe high metalmodels,sometimesbyasmuchafactorof reaction ofHCSwithO(reaction2164).Theis of reactionssulfurwithcarbon-bearingmolecules(see peratures sincenotemperature dependenceisincluded ference withearlierworkinwhichabarrierwasnot noted thatthereactionofCSwithoxygenhasan of CH(Fig.13).PrasadandHuntress(1980a)have Fig. 12).ThemoleculeCSisproducedbyreactionsofS rate constantthatresultsfor reaction2171atlowtem- of CSandOCSthussharesmanythefeaturesthat tion ofCHwithoxygen.Thetime-dependentevolution tion 2173)whichweassumeproceedsasdoesthereac- formed primarilyfromCHreactingwithsulfur(reac- changes dramaticallywithdecreasingelectronabun- largely fromCH+NandbecausetheCHabundance quite sensitivetothesevariablesbecauseitisproduced electron abundances.Incontrast,themoleculeCNis relatively constantoverawiderangeofdensitiesand No. 3,1982DENSEINTERSTELLARCLOUDCHEMISTRY351 (which formsCS),andofthe relativelysmallerreaction of CH(whichformsHCS) being largerthanthatofCH h(H) >10cm,whereCHismoderatelyabundant. demonstrates thatCSandOCSaremostabundantat assumed (OppenheimerandDalgamo19746).Table9 CS atlowtemperatures(reaction2150);thisisadif- activation barrierwhichwillinhibitthedestructionof dance andincreasingn(H). 10 (seeTable9).Thisisaconsequence oftheabundance 2 2 2 2 2 The chemistrythatproducesmoleculescontaining The OCSmoleculeismoreabundantthanCSinthe © American Astronomical Society •Provided by theNASA Astrophysics DataSystem vi) SulfurChemistry:CS,OCS 4 3 3 2 4 3 2 3 5 4 3 5 4 3 2.5 X10 2.5 X10 5.0X10 5.0X10 2.5X10 2.5 X10 5.0X10 5.0X10 1.0X10 1.0X10 1.0X10 1.0X10 1.0X10 1.0X10 -3 h(H) cm 2 8 Fractional AbundancesoftheOxygenFamilyat10Years 4.7(-5) 2.6(—4) 3.1(-4) 3-3(—4) 3.4(—4) 3.6(-5) 6.5(-5) 3.0(—4) 3.4( —4) 5.6( —5) 7.6(-5) 9.6(-5) 1.4(—4) 1.2(-4) x(0) 2.8(—8) 4.5(-8) 4.6(-7) 21(—8) 6-7( —8) 6.1(-8) 2.1(-7) 2.6( —6) 3-7(—6) x(OH) 8.1(-7) 1.9(-8) 1.3(-8) L7(—8) 1.4(—6) High Metals Low Metals TABLE? + :23 58 + -35+ + + x(H0) 2 6.4(—6) 6.3(-7) 6.6(—6) 3.6(-7) 7.1(-6) 7.6(—6) 8.1(-6) 9.6(-6) 9-7(—6) 8.8(—6) 1.9(-7) 1.4(-7) l.l(-7) 1.2(-7) exhibit thesamequalitative evolution. x(He). Inthiscaseessentially alloftheCisconverted metal model,«(H)=5X10cm~,thefractionalelec- little variationwithtimefrom10toyr. to CO.Sinceathigherdensities theelectronfractional largely dominatedbyHe,SandSi.Thecorrela- abundance isevensmaller, all thesemodelcalculations tron abundanceissmall enough sothatjc(H^")> metals. with S)andareneutralizedbychargetransfer abundance isshowninFigure14.Theregenerally here thesulfurisessentiallyneutral.Ath(H)=500 in reaction2173.TheOCSandCSabundancesare tion ofthemetalionswithtime-dependentelectron seen inTable10.Atlowerdensitiestheionabundanceis decrease byanorderofmagnitude,athigherdensities cm ittakesonly~10yrfortheSabundanceto third oftheionabundanceathigherdensities,ascanbe sulfur ionsareproducedbychargeexchange(e.g.,H this recombinationisevenfaster.Afterrecombination, (e.g., HeandHJ)butnotbyneutrals. comparable inthelowmetalmodels.BothCSandOCS sented; itcanbeseenthatforthedensitiesconsidered at lowtemperaturessincetheyaredestroyedbyions are relativelystableandabundantmolecules 2 2 + At longtimesthemetalionsmakeupmorethana Even atthelowestdensityconsideredforlow In Table9theSandabundancesarealsopre- c) GeneralComparisonofLowandHighMetal 6.8( —8) 3.0(-5) 8.0( —8) 7.0( —8) 6.7(-8) 7.8( —8) 7.8( —8) 7- 5(—5) 7.0(-5) 6- 5(—5) 5.9( —5) 4-8( —5) 3.5(-5) 8.0(-5) x(0) 2 vii) Metals Models x(CO) 5-2(—5) 2.3(-5) 8.7(-5) 3-4( —5) 8.6(—6) 1.5(—4) 1.3(-5) 1.5(-4) 1.5(—4) 1.5(-4) 1.5(-4) 1.5(-4) 1.5(-4) 1.5(-4) (HIGH METAL ABUNDANCE) (HIGH METAL ABUNDANCE)
Fig. 9.—Relative abundances of selected 0„H„ species as functions of cloud age and cloud density; shown are OH, H20, and 02. At 7 large electron abundances and high density, it takes 10 yr to reach stable values for 02 and H20. The OH abundance at late times is not as 6 5 large as that of H20 because OH serves as a source for the formation of 02. The abrupt changes in abundance at ~ 10 yr correspond to the time when the ion-molecule reactions that destroy 0„H„ species and create CO become insignificant.
© American Astronomical Society • Provided by the NASA Astrophysics Data System 1982ApJS. . .48. .32 IG © American Astronomical Society •Provided by theNASA Astrophysics DataSystem (HIGH METALABUNDANCE) (LOW METALABUNDANCE) Fig. 9.—Continued 0 2 o 2 DENSE INTERSTELLARCLOUDCHEMISTRY ¿-6 3- + 56 6 5 5-3 low metalmodel,andcomparisons aremadeherewith particular interest:temperature,cosmic-rayionization parameters. Someoftheseparameterscannotbedefini- rate, initialionizationofcarbon, andmetalabundance. made suchstudies,however,forfourparametersof in theparameters. Most ofthesesensitivitystudies areperformedwiththe desirable toassesstheresponseofmodelchanges dense clouds.Ineachoftheabovecasesitistherefore the calculationforh(H) = 2.5X10cmandT— the parameterscontainedinourcalculations.Wehave tively specified;othersareknowntovaryindifferent clouds requirethespecificationofanumberdifferent molecular abundancesgiventhewiderangeofcondi- els. our knowledgeoftheparametricvaluesinpresentmod- tions foundininterstellarcloudsandtheuncertainty 10 K. x(He). Inthesecasestheinitiallyionizedcarbonre- is intheformofCO.Intimeperiod10to4X10yr years theH^“ionsconvertCintotracemolecules(e.g., bearing moleculessuchasCH,CH,andO.In of thistime,~4X10yr,morethan99%thecarbon combines inlessthan10yr.Overthenextfewmillion contrast, theoxygen-bearingmoleculesOHandH0 CH, CH,etc.)whichthenreacttoformCO.Attheend 2 nearly allthecarbonandoxygenhavesimilar chemistry efficientlyconvertsCandOintomolecules, directly fromtheH^"+0reaction. the lowmetalmodelcloselyresemblesthatfor«(H)= be basedonaknowledgeofthedensity,temperature, between thetwomodels.Forexample,CSandOCS cant differencesariseintheabundancesofthesemole- show muchlesstimevariationsincetheyareformed models differsignificantlyforsomespecies.Thechoice cules inthetwomodels.Formost(butnotall)of abundances inbothmodels.Atlowerdensities,signifi- the relativelystablemoleculesCO,H0,and0contain there arelargevariationsintheabundancesofcarbon- § V.Bothmodelsmaybeapplicabletotheevaluationof of amodelforcomparisonwithobservationaldatamust models. model thaninthehighmetalmodel,whileHCNand and electronabundance;thisisdiscussedindetail HCO aresimilar(withinafactoroffew)inboth abundances areconsiderablysmallerinthelowmetal trace speciestherearelargevariationsinabundances 10 cmofthehighmetalmodelforwhichx(H^)> 2 2 2 2 2 2 4-3 It isnottractabletoperformsensitivitystudiesforall Detailed calculationsofthechemistryinterstellar The time-dependentbehavioroftheabundances At highdensities[«(H)>2.5X10cm],wherethe In conclusion,theabundancescalculatedforboth 2 rv. SENSITIVITYSTUDIES 353 1982ApJS. . .48. .32 IG results ofincreasingthetemperature to25Karegiven. many clouds,andthesensitivity analysisthusexplores caption forexplanationofsymbols). In generalthefractionalabundances varyonlyslightly of differenttemperature.In column(3)ofTable11the expected differencesincloud chemistryamongregions reaction ofhydrogenatedcarbonswithatomicnitrogenandarethuscloselylinkedtotheevolutionionizedneutralcarbon(see Fig.4 354 4 3 3 2 8 4 3 3 5 4 2 3 5 4 3 2.5 X107.1(—7)1.8(—8) 2.5 X105.6(—7)5.0(—9) 5.0X10 6.9(—7)7.4(—9) 5.0X10 2.7(—7)4.3(—9) Fractional AbundancesoftheC-NFamilyat10Years 2.5X10 2.3(—10)4.1(—9) 5.0X10 1.7(—9)5.6(—9) 2.5X10 4.2(—9)7.4(—9) L0X10 1.4(—10)1.3(—9) L0X10 7.9(—7)1.4(—8) 5.0X10 3.6(—8)1.5(—8) L0X10 3.7(—7)4.5(—9) 1.0X10 4.9(—11)4.1(—9) 1.0X10 6.9(—10)4.6(—9) 1.0X10 1.5(—8)1.2(—8) Temperature canbereasonablywelldeterminedfor Fig. 10.—ChemicalreactionflowdiagramforinteractionsoftheC„H„andNH„famihes.BothCNHCNareformedfrom the © American Astronomical Society •Provided by theNASA Astrophysics DataSystem -3 (cm) x(CN)x(HCN) n(U) 2 a) Temperature High Metals Low Metals TABLE 8 GRAEDEL, LANGER,ANDFRERKING 17 16 + 18- + 13 in therange£=3X10“to 3X10“(Wootten,Loren, explore thesensitivityof latetimeabundancesof limit tothetotalcosmic-rayionizationratehasbeen estimated fromobservationsofHCOandDCOtobe the effectsofloweringionization ratefromr„=ix atoms andmoleculestothe cosmic-rayionizationrate, and Snell1982;Guélin,Langer, andWilson1982).To also expected;itiscurrentlyestimatedbyextrapolating MeV) yieldalowerboundon^of3X10“s(Spitzer the knownhighenergyfluxtolowerenergies.Theupper to interactionswithhighenergycosmicrays(£’>100 reference totheprecedingdiscussions. p 1968). Acontributionfromlowenergycosmicraysis these carbonreservoirchangescanbeunderstoodby importantly, theratioofx(H^")tox(He)increases, temperatures. Themolecularabundancesthatresultfrom converting CtoCOmoreefficientlythanatlower in termsofthetemperaturedependencerecombi- nation rates,whichdecreaseasTincreases.Asexpected, are, however,sensitivetotemperaturebecauseofthe with temperatureasdotherateconstants.(Thevari- slightly highervaluesofx(e)andx(H^")result.More dances arethesubjectofPaperII.) exchange reactions408and1004;theseisotopicabun- exponential dependenceontemperatureoftheisotopic ations oflessabundantisotopicspeciescontainingC Assessments oftheionizationatomichydrogendue The variationsinabundancecanbestbeunderstood b) Cosmic-RayFlux 1982ApJS. . .48. .32 IG correlation oftheevolutionC with thoseofCNandHCN. Fig. 11.—Relativeabundances of CNandHCNasfunctionscloudagedensity. ComparisonwithFig.5showsthe © American Astronomical Society •Provided by theNASA Astrophysics DataSystem (HIGH METALABUNDANCE) CN (HIGH METALABUNDANCE) HCN 1982ApJS. . .48. .32 IG 7 + 178- + a -3 ion-molecule chemistryconvertsatomicneutralsto yr toreachstableconcentrations;thisis~3timeslarger molecules. Forthelowerrateofionizationittakes~10 decrease. Theresultisadecreaseoftherateatwhich fractional abundancesofx(e),andx(He) carbon-sulfur molecules(seeFig.4captionforexplanationofsymbols). than forthestandardionizationrate(seeFig.15). the resultsareshowninTable11.Asexpected, 356 GRAEDEL,LANGER,ANDFRERKING 10“ s“to^=3X10“shavebeencalculated; cosmic-ray fluxesistheincreasedtotalconversionof CO fromCandtheconsequentdecreaseinC,although Oppenheimer andDalgamo1974û;Elmegreen1979). an increased«(H^)/«(FIe)ratio,whichcanbe at latertimes(seeFig.16).Thisoccursbecauseof shown tobeproportional?~,where0
Fig. 14.—Relative abundances of electrons and chemically related positive ions as functions of cloud age and cloud density; shown are e, M +, Si+, and S+. Initially the electron abundance is controlled by that of ionized carbon. As the carbon is incorporated into molecules, the electron abundance is determined by the heavy element abundances.
360
© American Astronomical Society • Provided by the NASA Astrophysics Data System 1982ApJS. . .48. .32 IG © American Astronomical Society •Provided by theNASA Astrophysics DataSystem (HIGH METALABUNDANCE) (LOW METALABUNDANCE) + Si sr Fig. 14.—Continued i 361 (HIGH METALABUNDANCE) (LOW METALABUNDANCE) + S + s I—Io 00C\] 362 GRAEDEL, LANGER, AND FRERKING TABLE 11 i-D 8 3 -3 CL Sensitivity Studies: 10 yr with «(H2) = 2.5 X10 cm
»(x)/h(H2) Low Low Metals Low Metals Low Metals Intermediate High Species Metals 7’= 25 K = 3X10-18 s C+(/ = 0) = 0 Metals Metals (1) (2) (3) (4) (5) (6) (7) e 1.5( —7) 1.7(—7) 8.5(-8) L5( —7) 3- 6.5( —6) 4< —6) He+ . 3.7( —9) 3.7( —9) l.l(-9) 3.7(—9) 7.3( —9) 8.8( —9) C+ .. 9.0( —9) 8.6(-9) 2.5(-9) 9.0( —9) 7.3( —7) 2.3( — 7) M+ .. 2.4(-8) 2.4(-8) 2.3(—8) 2-4( —8) 2.5(-7) 2.5(-6) Si+ .. 1.4(-8) L4(—8) 1.2(-8) 1.4(-8) 1.6(-7) 1.5(-6) S+ ... 5.0(-8) 4.8(—8) 2.3( —8) 5.0(-8) l-4( —6) 2-2( —6) H? •• 1.6(-8) 1.9(-8) 6.2(-9) L6( —8) 1.7(-9) 9.1(—10) HCO l-4( —8) 3.0( —8) 9.0( —9) 1.4(-8) 5.1(-11) l.l(-U) C 4.4( —9) 3.0(—9) 7.8(—10) 4.4( —9) 9.7(-5) 1.2(-4) M ... 2.1(-9) 2.1(-9) 3.2( —9) 2.1(-9) 9.6(-9) 9-4{ —8) O..... 7-6(—5) 6.7( —5) 5.9(-5) 7.6(-5) 3.0(—4) 3.3(-4) S 1.2(-7) 1.2(-7) 1.4(-7) l-2( —7) 2.2( —7) 1.3(-5) c2... 2.1(—10) 1.3( —10) 4-2(—11) 2.1( —10) 4.0( —8) 1.4( —8) o2... 5.9(-5) 6.4{-5) 6.9(-5) 5-9( —5) 4.8( —8) 6.8( —8) CH .. 3.5(—10) 2.0( —10) 8.2(—11) 3.5(—10) 1.5( —8) 6.9(-9) CN .. 4-2(—9) 2-5( —9) 8.8(—10) 4.2( —9) 1.4(—6) 5.6(-7) CO .. 1.5(-4) 1.5(-4) 1.5(-4) 15( —4) 4- 2.3(-5) 7( —5) cs... 6.6(—10) 5.2( —10) 9.6(—10) 6.6(—10) 4.8( —9) 7.6( —8) OH .. 1.4(—6) 1.0( —6) 5.3(-7) 1.4( —6) 4-7( —8) 2.8( —8) C2H . 4.8( —10) 2.8( —10) 1.2(—10) 4.8( —10) 2.7( —8) 2-l( —8) CH2 . 1.0(—9) 6.6(—10) 3.2(—10) 10( —9) 2.9( —8) 2.2( —8) 8.8( —6) 8-2( —6) 7.7(-6) 8.8( —8) 6-9( —8) L4( —7) HCN 7.4(—9) 7.2( —9) 4.8( —9) 7.4( —9) 2.6(-9) 5.0( —9) OCS . 3.7(—10) 2.4(—10) 4.3(—10) 3.7( —10) 2.2( —8) 8.8( —7) ch3 . 8.7(—11) 7-l(—11) 3.9( —11) 8.7(—11) 3.4( —10) 8.4( —11) 2.3(—9) 2.3( —9) 2.3( —9) 2.3( —9) 6.6( —10) 7.1(—10)
2. Neutral carbon, recently detected by Phillips ei al. (1980) in interstellar clouds, is a third species of great chemical importance. At the present early stage of C observations, no data from cold, dense clouds are avail- able. Nonetheless, both models can satisfactorily repro- duce the observed C abundance, but at quite different values of density and time. Significant abundances of neutral carbon are predicted at early times ( < 106 yr) or 4 -3 at low densities [w(H2)< fewX 10 cm ] by the high metal abundance model and only at early times at all densities by the low metal abundance model. The ob- served C abundance appears to require either high elec- tron abundance or young cloud age ( < fewX 105 yr); the former condition is possible given high metal abun- dance. 3. The molecules CH and C2H, whose abundances are linked to a large degree with that of carbon, show considerable variation with density in both models. The latter molecule shows significant time variations as well. The abundance of CH becomes relatively stable at ~ 106 Fig. 15.—The evolution of the relative carbon reservoir abun- 4 yr, while the C2H abundance in the low metal abun- dances of C and CO for computations with n(H2) = 1.0X10 dance model evolves throughout the period shown in cm-3, 7’ = 10 K, and different cosmic-ray ionization flux values: 17 _l -18 _1 Figure Mb. The observed and calculated abundances are = 1X10“ s ( ), Hp = 3X10 s ( ). Decreasing ionization rate decreases the rate at which the ion-molecule in good agreement, but for different conditions of den- chemistry converts neutral atoms to molecules. sity and time in the two models.
© American Astronomical Society • Provided by the NASA Astrophysics Data System |- CTi co GO 00 C\] O D a
10 RELATIVE ABUNDANCE 4 5 8 7 6 3 9 10-- -12L 10 10 10‘- 10* 10' © American Astronomical Society •Provided by theNASA Astrophysics DataSystem 10- 10’ 10*i- 10-- 1-11 ä z o UJ > UJ < m r> z o: Ul _i 4 13 10 10-’— 10 10 IO 10-- io- io 10 IO ,-10 1*15 .-12 ,-11 .-«r- ,-8_ ,-9 CH + HC0 C3HIGH METALS ^ LOWMETALS E3OBSERVED KEY C^ C Fig. 16a FlG. 16fc CS CO 3 3 4 4 5 ♦ n(H)=5x10 ’'n(H) =1x10 ■ n(H)=2.5xio • n(H)=1Xio * n(H)=1xio 2 2 2 2 2 5 3 4 3 4 .*• n(H)=1Xio 2 ♦n(H)= 5x10 •n(H2> =1x10 ’ n(H)=1x10 ■ n(H)=2.5x10 2 2 2 HCN + 5-3 83- + lated relativeabundancesfromthelow NH, Snyderetal(1977);CO,En- been used:electrons,Langeretal The finalcalculatedabundancesare relative abundancesderivedfromob- Tucker etal(1976),Dickman(1978), (1978), Wootten,Snell,andGlassgold (1978), Watson,Snyder,andHollis of theobservations.Thefollowing h(H) 10*3^ l_o a icr4- io*5- UJ g 10'6 OH ñ i io-7k < 1 ^ 10-Ö § ^ 10-9 HCN KEY 10-1°- WOBSERVED • 105 YR ^LOW METALS ■10® YR 101-11 □ HIGH METALS *107 YR 12 lo- *- Fig. \la 10*5i- 10‘6- 10_7l 10'® UJ ü z n2h < 9 VZA o 10* z 3 m < 10'10 ai > 10-11 UJ CH C2H o: 10 12 _ KEY 5 10'13 W OBSERVED MO YR ^ LOW METALS 1 -106 YR 7 10'14 □ HIGH METALS J [* 10 YR 15 10' L Fig. \lb 4 3 5 7 Fig. 17.—Same as Fig. 16, but for calculations at h(H2) = l.OX 10 cm , r= 10 K, covering a cloud lifetime range of 10 -10 yr. The changes in concentration between 107 and 108 yr are too small to be seen on this figure. © American Astronomical Society • Provided by the NASA Astrophysics Data System 1982ApJS. . .48. .32 IG + + + + + + -86 + 57 3 -3 paper tobeacontrollingfactorinthetheoreticalde- in Figures16and17provideadditionalsupportforlow model. Sincetheformationanddestructionchemistryof only withthepredictionsoflowmetalabundance cold denseclouds,likethatofelectrons,isinagreement HCO involveselectronreactionsandappearstobe quite comparablewiththosederivedfromthelowmetal derived fromthehighmetalabundancemodelbutare Loren, andSnell1982;Guélin,Langer,Wilson et al.1978;Watson,Snyder,andHolhsWootten, dances indensecoresofdarkcloudshavebeende- extremely significantthatelectronfractionalabun- produces fartoomuchCS.Thetimeevolutionofits Tables 4and6).Theobservationsthusprovideaddi- which HCOandCOaredepletedinjustthatway(see magnitude smallerthanincolddenseregions,andCO regions, HCOabundancesaresometwoordersof electron abundancesinthosecolddensecloudswhich reasonably wellestabhshed,theHCOabundanceplots regarded asincorrect. metal abundancemodelatlongtimes;theother molecule whoseabundance,likethatofHCOand electron densitiesaresomewhatlarger.Thissituationis HCO measurementshavebeenmade.Inwarmerdense abundance model. termined tobeintherange3X1010(Langer termination ofthemolecularabundances.Itistherefore predicts decreasesinabundancewithtimeforboth in certaintimeanddensityregimes.Thepredictionfor dances ofNHandNH,althoughthelowmetal electrons, ispredictedsatisfactorilyonlybythelow generation producedbyelectronabundancevariations. analogous toourhighmetalabundancecalculations,in etal. 1978;Wootten,Snell,andEvans1980),while abundances maybesomewhatsmalleraswell(Wootten dance ofCNisreasonablywellpredictedbyourmodels atomic nitrogen,asoutlinedhere,mustthereforebe aspects oftheion-moleculechemistrybeginningwith abundance modelisthebetteroftwo.Thebasic times, butnotatintermediatetimes. abundance modelatearly(10yr)andlate agrees bestwiththosecalculatedfromthelowmetal abundance isunusualinthattheobserved tional evidenceofthedramaticeffectsonmolecular portance ofcloudageinthe comparisonofobserva- evidence wasfoundbyTurner andThaddeus(1977)in HCN isbetterstill.Thelowmetalabundancemodel their emissionmappingofa numberofmolecularcloud species atw(H)>fewX10 cm,apatternforwhich structures. Thisagreementemphasizes thepotentialim- 1982). Theseabundancesaresignificantlylessthanthose 32 2 + + 4. Theelectronabundancehasbeenshowninthis 5. TheobservedabundanceofHCOinthecores 6. Carbonmonosulfideisarelativelywell-studied 7. Bothmodelsfailtoexplaintheobservedabun- 8. IncontrasttoNHandNH,theobservedabun- 32 © American Astronomical Society •Provided by theNASA Astrophysics DataSystem DENSE INTERSTELLARCLOUDCHEMISTRY + + + here istobecontinuedand extended.Amongthemost presence inourmodelsofabundantatomicnitrogento not. Theagreementbetweenobservationandtheoryof magnesium. Obviously,further laboratoryexperiments of nitrogen,sulfur,silicon, andthemetalsiron inapplicability oftheion-moleculechemistryinsome well-studied molecule.Earliermodelcalculationsgener- may suggest),theoreticalpredictionsofthedistribution nitrogen isintheformofN(asHobservations react withCH*.Ifasignificantamountofgaseous dance isespeciallysensitivetodensity;thatofHCN tional datawiththeoreticalpredictions.TheCNabun- are essentialifchemicalmodeling ofthetypepresented basic aspectsoftheion-moleculechemistry.Others, in thedensecloudion-moleculechemistry;thus, of productsthenitrogenchemistrywoulddiffersub- CN andHCNabundancesisaresult,inpart,ofthe tions whichhavebeendeemed crucialtothechemistries tory) measuredrateconstants.Ashasbeenstressed cases, orthelackofacorrectreactionsetand(labora- (and other)modelsandobservationsresultfromthe dances (seethediscussionin§Ill&iii).Theformationof good agreementwiththemeasuredabundancesofthis stantially fromthosepresentedhere. throughout thetext,littleisknownaboutmanyreac- to judgewhetherthislackofagreementbetweenthese our calculationandseemtobewellexplainedbythe (e.g., CO,HCO,OH)haveabundanceswhichagreewith chains. correct formulationoftheprincipalchemicalreaction ally fellshortofpredictingthecorrectHCOabun- such asNH,seemlesswellexplained.Itispremature chemistry. Severalofthereadilyobservablemolecules physical assumptionsofthelowmetalabundancemodel promise ofprovidinginformationabouttheage ranges of10speciesincold,densecloudsandfailsonly metal abundancemodel,incontrast,yieldsequilibrium successful inexplainingtheabundancesofonlyafew agreement oftheabundancesisgoodevidencefor this polyatomicmoleculeinvolvesseveralkeyreactions successes andthefailuresofagasphaseion-molecule dense cloud,materialfollowingitscollapseintoarela- C, HCO,andCOinwarmerdenseregions.Thelow shows promiseforexplainingobservedabundancesof abundances whichoverlaptheobservedabundance the observedspeciesincold,dark,densecloudsbut tively condensedstate,especiallyforcasesinwhichthe several ofthespecies(C,CH,CN,CS,CH,HCO)show for C,NH,andNH.Figure17demonstratesthat apply. 2 2 2 3 2 32 To summarize,thehighmetalabundancemodelis 9. Thecalculatedabundancesofformaldehydearein The modelcalculationspresentedhereshowboththe VI. DISCUSSION 365 1982ApJS. . .48. .32 IG 57 7 parison withobservationalabundances.Cloudage,from .1977,Ap./.,212,396. ing thelowelectronabundancemodelapplies,areneu- be seenthatafewspeciesvaryenough(>factorof10) dense dynamicallystableobject.Priortothistime,the the standpointofourmodelcalculations,refersto calculations isthedeterminationofcloudagesbycom- Anicich, V.G.,Huntress,W.T.,Jr., andFutrell,J.H.1976,Chem. Allen, M.,andRobinson,G.W.1976,Ap.J.,207,745. in mindthatitmaynotbeasimplemattertoreadthe most sensitiveindicatorswithinthistimespan,provid- of youth”forthedensestagescloudevolution.The during thetimespan10toyraftercloudcondensa- gen atomabundance.Estimationofcloudagesby age canperhapsbebestassessedbytheresidualhydro- Black, J.H.,Dalgamo,A.,andOppenheimer, M.1975,Ap.J.,199, Black, J.H.,andDalgamo,A.1977, Ap.J.Suppl.,34,405. Black, J.H.1975,Ph.D.thesis,Harvard University. Allen, T.L.,Goddard,J.D.,andSchaefer,H.F.,III.1980, Allen, M.,andKnapp,G.R.1978,Ap.J.,225,843. Albritton, D.L.,Viggiano,A.A.,Dotan,L,andFehsenfeld,F.C. porating ahydrodynamiccomponentsuchasthatde- production duringtheearly(lowdensity)stagesofcloud selection ofappropriatemolecules.InFigure17itcan analyses ofmolecularabundanceratiosrequirescareful time elapsedsincethediffusecloudcontractedintoa Albritton, D.L.1978,AtomicDataNucl.Tables,22,1. veloped byGerolaandGlassgold(1978). models presentedheredonotaccountformolecular CH,CH,CN,H2CO); acomparisonoftheCandCO tion tobeusedestimateage,i.e.,serveas“tracers carbon andoxygenfamilyofmolecules.Finally,the h(H). Todetermineagesbeyond10yrrequiresa figures becausecloudsevolveindensityaswelltime abundances maybemostusefulofall.Itshouldkept tral carbonanditsimmediatederivatives(e.g., forcing agreementbetweencalculationanddata).A enter intoextensivediscussionofpossibleadjustments clouds andoftheapplicabilityavailableobserva- evolution. Suchananalysisrequiresacalculationincor- species withalongerevolutionarytimethanthatofthe and the(critical)electronabundanceisafunctionof age ofaparticularstagecloud’sevolutionfromour important needsare:(i)determinationofthedegree to thechemicalsetusedinourcalculations(although tional information,itdoesnotappearproductiveto 366 such adjustmentsareoftenmadewiththeintentof determination oftherolegrainsinlossandgenera- (ii) determinationofthedegreechargeexchangein Hj transferinthereaction+A,where^4=N,S,Si; tion ofinterstellarmolecules. the reaction+M,whereM=Fe,Mg,etc.;(iii) 2 2 Phys. Letters.,40,223. Chem. Phys.,73,3255. 1979, J.Chem.Phys.,71,3295. A potentiallyusefulapplicationofchemicalmodel Because ofuncertaintiesininitialconditionsdense © American Astronomical Society •Provided by theNASA Astrophysics DataSystem GRAEDEL, LANGER,ANDFRERKING REFERENCES Dickman, R.L.1978,Ap.J.Suppl., TH,407. de Jong,T.,Dalgamo,A.,andBoland, W.1980,Astr.Ap.,91,68. Brown, J.M.,andThrush,B.A.1967,Trans.FaradaySoc.,63, Cupitt, L.T.,andGlass,G.P. 1975, Internat.J.Chem.Kinetic Crutcher, R.M.1979,Ap.J.,234, 881. Cravens, T.E.,andDalgamo,A. 1978,^4/?./.,219,750. Braun, W.,Bass,A.M.,Davis,D.D.,andSimmon,J.1969, Boden, J.C,andThrush,B.A.1968,Proc.Roy.Soc.London,A, Clyne, M.A.A.,andMcDermid,I.S.1975,J.Chem.Soc.Faraday Massachusetts. information onion-moleculechemistry,andthepro- provide aframeworkwithinwhichtoplacemuchofthe be mostuseful.Notwithstandingthesedifficulties,the laboratory programsandobservationalstudies;perhaps interstellar cloudchemistrymodelscanbeprovidedby completed whileW.D.L.wasattheUniversityof data priortoitspublication.Partofthisworkwas duction ofmoleculesastrophysicalinterest. clouds arereasonablywellunderstood.Assuch,they results presentedhereindicatethatmanyoftheprin- mechanism. Thedeterminationoftemperaturesand models unlessthoseobservationsaremadeforseveral P. GoldsmithandR.Linkeforprovidinguswiththeir and R.W.Wilsonforhelpfulcomments, cipal chemicalprocessesoccurringindenseinterstellar one oftheimportantconsequencesourworkisto chemical intermediate. of theimportantspeciesC,andH0,an electron abundancesisvital,asarefurtherobservations grain orion-moleculeformationasthechiefproduction (Langer etal.1979,1980h)oratleasttochoosebetween cases observationsofdeuteratedmoleculeshavehelped demonstrate thatitisdifficultforextensiveobservations describe thosedata. benchmarks againstwhichsucheffortsarebased.Until suggest specificareasinwhichtheeffortsofotherscan aging, itisclearthatmuchremainstobedone. sources. Isotopicobservationsareusefulaswell:insome species incommonphysicalregionsofeachseveral detailed accuracyofthechemicaltheorydevelopedto conceptual problemwith“chemicaljuggling”istherela- Guidance intheformulationandanalysisofresults sive, andagreementwithobservationaldataisencour- to elucidatethepathwaysofion-moleculechemistry to provideconstraintsoninterstellarcloudchemistry available, itisdifficultorimpossibletoevaluatethe observational dataofsufficientdetailandaccuracyare tively sparseandincompletelydefinedobservational 2 305, 107. 630. Symp., 1,39. Proc. Roy.Soc.London,A,312,417. Trans. I,71,2189. We wishtothankJ.Black,Kwan,A.Penzias, Although theresultspresentedinthispaperareexten- The wideabundancevariationsofFigures16and17 Vol. 48 No. 3, 1982 DENSE INTERSTELLAR CLOUD CHEMISTRY 367 Dunkin, D. B., Fehsenfeld, F. C, Schmeltekopf, A. L., and Langer, W. D., and Glassgold, A. E. 1976, Astr. Ap., 48, 395. Ferguson, E. E. 1968, J. Chem. Phys., 49, 1365. Langer, W. D., Frerking, M. A., Graedel, T. E., and Armentrout, Edelson, D. 1975, Computers and Chemistry, 1, 29. P. B. 1982, in preparation (Paper II). Elmegreen, B. G. 1979, Ap.J., 232, 729. Langer, W. D., Wilson, R. W., Henry, P. S., and Guélin, M. 1978, Encrenaz, P. J., Falgarone, E., and Lucas, R. 1975, Astr. Ap., 44, Ap.J. (Utters), 225, LI 39. 73. Laudenslager, J. B., and Huntress, W. T., Jr. 1974, Internat. J. Evans, N. J., Zuckerman, B., Morris, G., and Sato, T. 1975, Ap. J., Mass Spectrometry Ion Phys., 15, 223. 196, 433. Leu, M. T., Biondi, M. A., and Johnsen, R. 1973a, Phys. Rev. A, 1, Farrow, L. A., and Edelson, D. 1974, Internat. J. Chem. Kinetics, 292. 6, 787. L. 19736, Phys. Rev. A, 8, 420. Federman, S. R., Glassgold, A. E., and Kwan, J. 1979, Ap. J., 227, Liddy, J. P., Freeman, C. G., and McEwan, M. J. 1977, 466. M.N.R.A.S., 180, 683. Fehsenfeld, F. C. 1976, Ap. J., 209, 638. Linke, R. A., and Goldsmith, P. F. 1980, Ap.J., 235, 437. . 1980, I AU Symposium 87, Interstellar Molecules, ed. Mahoney, M. J., McCutcheon, W. H., and Shuter, W. L. H. 1976, B. Andrew (Dordrecht: Reidel), p. 291-296. A. J.,%\, 508. Fehsenfeld, F. C, and Ferguson, E. E. 1972, J. Chem. Phys., 56, Martin, R. N., and Barrett, A. H. 1977, Ap. J. Suppl., 36, 1. 3066. Mattila, K., Winnberg, A., and Grasshoff, M. 1979, Astr. Ap., 78, Ferguson, E. E. 1973, Atomic Data Nucl. Tables, 12, 159. 275. Field, G. B., and Steigman, G. 1971, Ap. J., 166, 59. McCutcheon, W. H., Shuter, W. L. H., and Booth, R. S. 1978, Fox, K., and Jennings, D. E. 1978, Ap. J. (Letters), 226, 43. M.N.R.A.S., 185, 755. Frerking, M. A., Langer, W. D., and Graedel, T. E. 1982, in McGowan, J. W., Mul, P. M., D’Angelo, V. S., Mitchell, J. B. A., preparation (Paper III). Defrance, P., and Froelich, H. R. 1979, Phys. Rev. Utters, 42, Frerking, M. A., Langer, W. D., and Wilson, R. W. 1982, Ap. J., in 373. press. Mehr, F. J., and Biondi, M. A. 1969, Phys. Rev., 181, 264. Gear, C. W. 1971, Comm. ACM, 14, 176. Minn, Y. K, and Greenberg, J. M. 1979, Astr. Ap., 77, 37. Gehnng, M., Hoyermann, K., Schecke, H., and Wolfrum, J. 1973, Mitchell, G. F. 1978, A.J., 83, 1612. 14th Internat. Symp. on Combustion (Pittsburgh: Combustion Mitchell, G. F., Ginsburg, J. L., and Kuntz, P. J. 1978, Ap. J. Institute), p. 99. Suppl., 38, 39. Gerola, H., and Glassgold, A. E. 1978, Ap. J. Suppl., 37, 1. Mul, P. M., and McGowan, J. W. 1979a, J. Phys. B., 12, 1591. Glassgold, A. E., and Langer, W. D. 1974, Ap. J., 193, 73. . 19796, Ap. J. (Utters), 227, L157. Goldan, P. D., Schmeltekopf, A. L., Fehsenfeld, F. C, Schiff, H. L, . 1980, Ap. J., 237, 749. and Ferguson, E. E. 1966, J. Chem. Phys., 44, 4095. Oppenheimer, M., and Dalgamo, A. 1974a, Ap. J., 187, 231. Goldsmith, P. F., Langer, W. D., Carlson, E. R., and Wilson, . 19746, Ap. J., 192, 29. R. W. 1980, I AU Symposium 87, Interstellar Molecules, ed. Penzias, A. A. 1980,1AU Symposium 87, Interstellar Molecules, ed. B. Andrew (Dordrecht: Reidel), p. 417-420. B. Andrews, (Dordrecht: Reidel), pp. 397-404. Green, S. 1981, Ann. Rev. Phys. Chem., 32, 103. Phillips, T. G., Huggins, P. J., Kuiper, T. B. H., and Miller, R. E. Guélin, M., Langer, W. D., Snell, R. L., and Wootten, H. A. 1977, 1980, Ap.J. (Utters), 238, LI 03. Ap. J. (Letters), 217, L165. Prasad, S. S., and Huntress, W. T., Jr. 1980 a, Ap.J. Suppl., 43, 1. Guélin, M., Langer, W. D., and Wilson, R. W. 1982, Astr. Ap., in . 19806, Ap. J., 239, 151. press. Rutherford, J. A., and Vroom, D. A. 1972, J. Chem. Phys., 57, Hampson, R. F., and Garvin, D. 1977, Reaction Rate and Pho- 3091. tochemical Data for Atmospheric Chemistry-1977 (NBS Spec. Rydbeck, O. Eo. H., Elldér, J., Irvine, W. M., Sume, A., and Pub. 513). Hjalmarson, Â. 1974, Astr. Ap., 34, 479. o Herbst, E., Bohme, D. K., Payzant, J. D., and Schiff, H. I. 1975, Rydbeck, O. E. H., Sume, A, Hjalmarson, A., Elldér, J., Rönnäng, Ap. J., 201, 603. B. O., and Kollberg, E. 1977, Ap. J. (Utters), 215, L35. Herbst, E., and Klemperer, W. 1973, Ap.J., 185, 505. Schiff, H. L, and Bohme, D. K. 1979, Ap. J., 232, 740. Ho, P. T. P., Martin, R. N., Myers, P. C., and Barrett, A. H. 1977, Scoville, N. Z., and Hersh, K. 1979, Ap. J., 229, 578. Ap.J. (Letters), 215, L29. Slagle, I. R., Pruss, F. J., Jr., and Gutman, D. 1974, Internat. J. Hudson, R. D., ed. 1977, Chlorofluoromethanes and the Stratosphere Chem. Kinetics, 6, 111. (NASA Ref. Pub. 1010). Smith, D., and Adams, N. G. 1978, Ap. J. (Utters), 220, L93. Huntress, W. T., Jr. 1977, Ap. J. Suppl., 33, 495. . 1980, Ap. J., 242, 424. Huntress, W. T., Jr., Kim, J. K., and Theard, L. P. 1974, Chem. Snell, R. L., Langer, W. D., and Frerking, M. A. 1982, Ap. J., in Phys. Letters, 29, 189. press. Huntress, W. T., Jr., and Pinizzotto, P. F. 1973, J. Chem. Phys., 59, Snyder, L. E., Hollis, J. M., Buhl, D., and Watson, W. D. 1977, Ap. 4742. J. (Utters), 218, L61. Iglesias, E. 1977, Ap. J., 218, 697. Solomon, P. M, and Klemperer, W. 1972, Ap. J., 178, 389. Iglesias, E., and Silk, J. \91%, Ap. J., 226, 851. Spitzer, L., Jr. 1968, Diffuse Matter in Space (New York: Wiley Johnsen, R., and Biondi, M. A. 1974, Icarus, 23, 139. and Sons). Johnsen, R., Chen, A., and Biondi, M. A. 1980, J. Chem. Phys., 72, Spitzer, L., Jr., and Jenkins, E. B. 1975, Ann. Rev. Astr. Ap., 13, 3085. 133. de Jong, T., Dalgamo, A., and Boland, W. 1980, Astr. Ap., 91, 68. Thaddeus, P., Guélin, M., and Linke, R. A. 1981, Ap. J. (Utters), Kim, J. K., and Huntress, W. T., Jr. 1975, Internat. J. Mass 246,41. Spectrometry Ion Phys., 16, 451. Tucker, K. D., Dickman, R. L., Encrenaz, P. J., and Kutner, M. J. Kim, J. K., Theard, L. P., and Huntress, W. T., Jr. 1974, Internat. 1976, Ap. J., 210, 679. J. Mass Spectrometry Ion Phys., 15, 223. Tunder, R., Mayer, S., Cook, E., and Schnieper, L. 1967, Aero- . 1975a, Chem. Phys. Letters, 32, 610. space Corp. Rept. No. TR-001 (9210-02)-!. . 19756,/. Chem. Phys., 62, 45. Turner, B. E., and Thaddeus, P. 1977, Ap. J., 211, 755. Kwan, J. 1979, Ap. J., 229, 567. Turner, J. L., and Dalgamo, A. 1977, Ap. J., 213, 386. Lada, C. J., Oppenheimer, M., and Hartquist, T. W. 1978, Ap. J. Umebayashi, T., and Nakano, T. 1980, Pub. Astr. Soc. Japan, 32, (Letters), 226, LI53. 405. Langer, W. Û. 1976, Ap. J., 206, 699. Viggiano, A. A., Howorka, F., Albritton, D. L., Fehsenfeld, F. C, . 1977, Ap. J. (Utters), 212, L39. Adams, N. G., and Smith, D. 1980, Ap. J., 236, 492. . 1978, Ap. J., 225, 860. Washida, N., Martinez, R. R., and Bayes, K. D. 1974, Zs. Natur- Langer, W. D., Goldsmith, P. F., Carlson, E. R., and Wilson, forschung, A29, 251. R. W. 1980a, Ap. J. (Utters), 235, L39. Watson, W. D. 1973, Ap. J. (Utters), 183, L17. Langer, W. D., Schloerb, F. P., Snell, R. L., and Young, J. 19806, . 1976, Rev. Mod. Phys., 48, 513. Ap. J. (Utters), 239, L125. © American Astronomical Society • Provided by the NASA Astrophysics Data System 368 GRAEDEL, LANGER, AND FRERKING Watson, W. D., Anicich, V. G., and Huntress, W. T., Jr. 1976, Ap. Wootten, H. A., Bozyan, E. P., Garrett, D. B., Loren, R. B., and J. {Letters), 205, L165. Snell, R. L. 1980, Ap. J., 239, 844. Watson, W. D., Snyder, L. E., and Hollis, J. M. 1978, Ap. J. Wootten, H. A., Evans, N. J., Snell, R. L., and Vanden Bout, P. {Letters), 222, LI45. 1978, Ap. J. {Utters), 225, L143. Weisheit, J. C, and Upham, R. J., Jr. 1978, M.N.R.A.S., 184, 227. Wootten, H. A., Loren, R. B., and Snell, R. L. 1982, Ap. J., in Weller, C. S., and Biondi, M. A. 1968, Phys. Rev., 181, 264. press. Westenberg, A. A., and deHaas, N. 1972, J. Phys. Chem., 76, 2215. Wootten, H. A., Snell, R., and Evans, N. J., II. 1980, Ap. J., 240, Wilson, R. W., Langer, W. D., and Goldsmith, P. F. 1981, 4?. /. 532. (Letters), 243, 47. Wootten, H. A., Snell, R. L., and Glassgold, A. E. 1979, Ap. J., Wilson, T. L., and Minn, Y. K. 1977, Astr. Ap., 54, 933. 234, 876. Wilson, W. E., Jr. 1972, J. Phys. Chem. Ref. Data. 1, 535. Zuckerman, B., and Turner, B. E. 1975, Ap. J., 197, 123. Margaret A. Frerking: Jet Propulsion Laboratory, Mail Stop 168-314, Pasadena, CA 91103 T. E. Graedel: Bell Laboratories, Murray Hill, NJ 07974 William D. Langer: Princeton University, PO Box 451, Princeton, NJ 08544 © American Astronomical Society • Provided by the NASA Astrophysics Data System