Ionized Nitrogen Mono-hydride Bands are Identified in the Pre-solar and Carbonado Diamond Spectra J. GARAI1,2*
1Department of Mechanical and Materials Engineering, Florida International University, Miami, FL 33199 2 Department of Mechanical and Structural Engineering, Ybl Miklós Faculty, Szent István University, Budapest, Hungary
E-mail: [email protected]
Abstract-None of the well established Nitrogen related IR absorption bands, common in synthetic and terrestrial diamonds, have been identified in the pre- solar diamond spectra. In the carbonado diamond spectra only the single nitrogen impurity (C centre) is identified and the assignments of the rest of the nitrogen-related bands are still debated. It is speculated that the unidentified bands in the Nitrogen absorption region are not induced by Nitrogen but rather by Nitrogen-hydrides because in the interstellar environment Nitrogen reacts with + Hydrogen and forms NH ; NH; NH2; NH3. Among these Hydrides the electronic configuration of NH+ is the closest to Carbon. Thus this ionized Nitrogen-mono- hydride is the best candidate to substitute Carbon in the diamond structure. The bands of the substitutional NH+ defect are deduced by red shifting the irradiation induced N+ bands due to the mass of the additional Hydrogen. The six bands of the NH+ defects are identified in both the pre-solar and the carbonado diamond spectra. The new assignments identify all of the nitrogen-related bands in the spectra, indicating that pre-solar and carbonado diamonds contain only single nitrogen impurities.
INTRODUCTION
Nitrogen is the most important impurity in diamonds. The content and the type of the nitrogen defects are even used to classify the diamonds (Davis, 1977). If the nitrogen content is significant, typically measured in ppm but can be as high as 1%, then the diamonds are Type I while diamonds with undetectable or very small amounts of nitrogen are Type II. When a diamond forms, nitrogen atoms can replace the carbon atoms, forming an isolated single impurity. Thus newly formed diamonds, like synthetic diamonds, almost exclusively contain single nitrogen impurities. Energetically, a higher level of aggregation of nitrogen impurities is
1 favored, single nitrogen impurities tend to unify and form higher levels of aggregation. The bonds between the carbon atoms in diamonds are very strong resulting in very slow diffusion, even on the time scale of a billion years. Elevated pressures and temperatures increase diffusion rates resulting in higher levels of aggregation, clustering two, four, or more nitrogen atoms. The aggregation level of nitrogen can be used to estimate the mantle residence time for terrestrial diamonds. The lack of higher level nitrogen aggregation indicates that diamonds were not affected by high pressures and temperatures and long annealing times after formation. The nano-size of the pre-solar diamonds, which typically contain in the order of 103 C atoms and 10 N atoms (Jones & d’Hendecourt, 2000; Jones, 2001), might put constraints on the Nitrogen aggregation. About 98% of natural terrestrial diamonds contain defects with 2 and 4 aggregated nitrogen atoms. Based on the aggregation level of the nitrogen, Type I diamonds are subdivided into two subgroups. Type Ia diamonds (98%) contain clustered nitrogen atoms, and Type Ib (0.1%) contain scattered or single nitrogen atoms. Type II diamonds are also subdivided into Type IIa (1-2%), which is almost pure carbon, and to Type IIb (0.1%) containing boron atoms. The percentages refer to the natural occurrence of different diamond types. The aggregation level of nitrogen can be identified by infrared absorption. The single (C center), pair (A center), four (B center) nitrogen and higher aggregations, like platelets each induce well-defined characteristic infrared absorption bands. These nitrogen-related bands are present in terrestrial and synthetic diamonds but lacking in the pre-solar diamond IR spectra (Lewis et al. 1989; Colangeli et al. 1994; Koike et al. 1995; Mutschke et al. 1995; Hill et al. 1997; Andersen et al. 1998; Braatz et al. 2000). The spectra of carbonado diamond contain the bands relating to substitutional N defects at 1130 cm-1 and 1344 cm-1; however, the spectra is very different from type Ib diamonds (Fig. 1) and contains many additional unidentified bands in the Nitrogen region. No other bands relating to higher nitrogen aggregation are present in the spectra. The rest of the characteristics bands identified in the carbonado diamond spectra (Garai et al. 2006; Kagi and Fukura 2008) are similar to the pre-solar bands; therefore, these diamonds are also included in this investigation. It should be noted that the origin of carbonado remains enigmatic. The almost identical IR spectra are not an ultimate proof for same origin and formation. The assignments of the nitrogen-related bands in the pre-solar and carbonado diamonds spectra are still debated and the exact configuration of N is not known.
2 NITROGEN IN INTERSTELLAR SPACE
The nitrogen in the Hydrogen rich enviroment of interstellar space can react with Hydrogen forming nitrogen hydrides. The nitrogen molecule N2 can disassociate through the reaction forming N+ (Adams & Smith, 1984) + + He + N2 → (N 2)* + He + + (N 2)* → N 2 + hν + → N + N + The kinetic energy of this reaction is 0.28 eV, which is expected to equally divided between N and N. This energy is sufficient to overcome on the endoergicity of reaction + + N + H2 → NH + H. Atomic nitrogen can also be ionized by cosmic rays in interstellar space N + hν → N+ + e-, or N + p → N+ + e- + p and form NH+ ion (Mitchell et al. 1978). NH+ can also be formed through charge transfer reaction from NH as: H+ + NH → NH+ + H, or through the exothermic reaction: + + H2 + N → NH + H, or can be synhetized from interstellar ammonia as: + + He + NH3 → NH + H2 + He, or through photolytic reaction (Huebner and Giguere, 1980) as + - NH3 → NH + H2 + e , or synthetized from HCO as: N+ + HCO → NH+ + CO, or through the ionizing reaction of NH + hν → NH+ + e-. + + In Hydrogen rich environment NH 2 and NH 3 can be formed as: + + NH + H2 → NH 2 + H and
+ + NH 2 + H2 → NH 3 + H
In reverse NH and NH2 can also been formed through the photochemical decomposition of NH3 (Kerns & Ducan, , 1972).
3 The exact mechanisms for formation of nitrogen hydrides in space enviroment are still debated; however, it is widly agreed and supported by observations that significant part of the nitrogen in + space is in the form of nitrogen hydrides (NH ; NH; NH2; NH3 ). Ammonia NH3, is widely observed in dark clouds and star-forming regions (Cheung et al. 1968). and the presence of nitrogen hydrites (NH and NH2 ) are well known in comets (e.g. Swings et al. 1941; Meier et al. 1998; Feldman et al. 1993). Both hydites, NH and NH2, have also been observed in stellar photospheres (e.g. Schmitt 1969; Farmer & Norton 1989). Interstellar NH was first detected in the diffuse clouds towards the star ξPer and HD 27778 by Meyer & Roth (1991). The presence of NH has also been detected in other regions (Goicoechea et al., 2000; Crawford & Williams, 1997; Hily-Blant et al., 2010; Persson et al., 2010). Significant concentration of NH+ ion in interstellar molecular cloud and in comets has been predicted by Almeida and Singh (1982) and detected by Persson et al. (2010). It can be concluded that in interstellar environment Nitrogen + reacts with Hydrogen and present in the form of Nirogen-hydrides NH ; NH; NH2; NH3.
DISCUSSION
In order to extract the pre-solar diamonds from meteorites, the samples go through severe chemical treatments, which alter the original spectra (Braatz et al. 2000). Based on these contaminations it has been concluded that in the pre-solar diamond IR spectra only the absorption features relating to nitrogen atoms (Braatz et al. 1999) and to the multiple phonon absorption of diamonds (Hill et al. 2000) can be considered as intrinsic properties of the diamond. In this study the absorption features of Nitrogen impurities are investigated. The complete data set of previous pre-solar and carbonado diamond IR spectra reported in the literature was collected. The characteristic bands are listed in Table 1. In the Nitrogen region the band at 1085 cm-1 has been proposed results from chemical treatment (Braatz et al. 2000). The spectra of carbonado diamond contain all of the reported bands of pre-solar diamonds with the exception of the 1085 cm-1. Since the carbonado samples were not chemically treated (Garai et al., 2006), the lack of the 1085 cm-1 band is consistent with the proposed chemical treatment-induced origin of this band. The band at 1285 cm-1, characteristic of A center in terrestrial diamonds, is reported in the Orgueil and the carbonado diamond spectra. This band is greatly diminished by further oxidation of the nano-diamond residues of Orgueil chondrite indicating that the band is an artifact resulting from the chemical treatments (Hill et al. 1997). This band is present in all of the chemically treated carbonado diamond spectra (Kagi & Fukura, 2008); however, it is also
4 detected in one of the non-treated carbonado spectra. Thus the possibility that this band might be induced by A centers can not be excluded. The characteristic bands of C centre at 1130 cm-1 and 1344 cm-1 are present in the spectra of carbonado diamond. In the Allende and Orgueil spectra there is a band at 1122-1125 but the 1344 cm-1 band is missing. Thus the presence of the substitutional Nitrogen impurities (C centre) is debatable in pre-solar diamonds. None of nitrogen related bands, common in terrestrial and synthetic diamonds, are uniquely identifiable in any of the pre-solar diamond spectra. Based on the lack of the well established Nitrogen related bands, it is speculated that the unidentified bands in the Nitrogen absorption region might not induced by Nitrogen but rather by Nitrogen-hydrides because in the Hydrogen + rich interstellar environment Nitrogen reacts with Hydrogen and forms NH ; NH; NH2; NH3. The bonds between N and C are covalent. Covalent bonds are directional and dictates the spatial arrangements of the atoms. Carbon atoms in the diamond structure have tetrahedron coordination based on the spatial distribution of the sp3 hybridized electrons. In order to fit into the diamond lattice the spatial distribution of the electrons of Nitrogen has to be the same. The electronic structure of Nitrogen is 2s2 2p3. The three bonding domains of the p electrons and the one nonbonding domain of the loan electron par electrons forms a tetrahedron skeleton structure which fits into the diamond lattice. Thus, the single nitrogen impurity in the diamond lattice is bonded to three of the neighboring carbon atom. This conclusion is supported by the existence of the NV defects. If Nitrogen would bonded to four carbon atoms then the NV defects in diamond would not be stable and NV defects would not exist permanently. The tetrahedron skeleton structure of the diamond lattice can also be achieved through the ionization of the Nitrogen. If Nitrogen is ionized then the remaining four electrons are hybridized to sp3. Thus N+ fits comfortably into the diamond lattice by forming four bonds. It can be predicted that among + + the available nitrogen hydrides (NH ; NH; NH2; NH3) the coordination of NH would preferentially fit into the bulk diamond lattice. Thus, it can be predicted that NH+ could substitute carbon in the diamond lattice and form an NH+ defect when nitrogen hydrides are present at the formation of the diamonds. The absorption features of the NH+ defects are not known. In an attempt to identify the features NH+ defects the bands of N+ defects were redshifted by increasing the mass of Nitrogen with one atomic units due to the mass of the additional Hydrogen. The ionization of the substitutional N (C center) and conversion into substitutional N+ (C+ center) has been predicted (Lawson & Kanfa 1993) and later experimentally verified by the irradiation of type Ib diamonds . The irradiation-induced C+ center exhibit a sharp peak at
5 1332 cm-1 and broader and weaker peaks at 1115 cm-1, 1046 cm-1, and 950 cm-1 in their spectra (Lawson et al. 1998). The same bands were observed in the spectra of synthetic diamonds after radiation damage by electrons (Collins et al. 1988) along with two additional bands at 1450 cm-1and 1502 cm-1 which have been assigned to C-N. All the bands of the C+ center are red shifted in the carbonado-diamond spectra with the exception of the band at 1332 cm-1 (Fig. 2-a). It has been shown experimentally that N15 isotope doping does not have an effect on the radiation-induced band at 1332 cm-1 (Samoilovitch et al. 1975). Thus no red shift is expected for the 1332 cm-1 band from the additional mass of Hydrogen. Using a simple force constant model the rest of the irradiation induced N+ bands are red shifted by adding one atomic unit to the mass of Nitrogen, due to the mass of the additional Hydrogen. The calculated absorption bands of the NH+ defects are listed in Table 2. The employed simple force constant model can be used and gives reasonably good results, when the bonds are uniform and spherically symmetric. The permanently positively charged Nitrogen with tetravalent bonds satisfies these requirements. The agreement between the red shifted substitutional N+ bands and the bands of the pre-solar and carbonado diamond spectra is very good. Based on this good agreement it is suggested that the ionized Nitrogen-mono-hydride complex bonded into the four neighboring carbon atoms and that the bands observed in the Nitrogen absorption region (Table 1) can be assigned to Substitutional NH+ defects. The presence of NH+ defects in carbonado diamonds is consistent with Hydrogen isotopic composition investigations, which report about 70 ±30 ppm of Hydrogen, relating to the bulk of the diamond (Demeny et al. 2011). The presence of NH+ defects in pre-solar and carbonado diamonds is also supported by the observed N-H-related bands. Both pre-solar (e.g., Andersen et al. 1998) and carbonado diamond spectra (Fig. 2-b) contain intense N-H-related stretching vibration bands in the region of 3100-3400 cm-1 and an N-H bending band at 1650 cm-1. These bands are absent or significantly weaker in the spectra of terrestrial and CVD diamonds (e.g., McNamara et al. 1994). The two steps formation of NH+ defect, ionizing the substitutional N0 or C center by irradiation and then hydrogenating the ionized nitrogen, might also be possible. However, no N +-related bands can be identified in any of the spectra. The complete lack of this “middle stage” defects in this two step formation process indicates that the NH+ defects were most likely formed by one step process. Thus the ionized Nitrogen Mono-hydrides were substituted into the diamond structure at the time of the formation. The NH+ related bands at 1420 cm-1 and 1465 cm-1 overlap with C-H deformation bands; therefore, both NH+ and C-H deformation is assigned to these bands.
6 Despite the similarities between the pre-solar and carbonado diamonds’ IR spectra, there are subtle differences. The substitutional NH+ band at 1332 cm-1 is reported only in the carbonado spectra. The nitrogen in carbonado-diamond is dominantly present in the form of NH+ defects but substitutional N0-related bands are also detectable in the spectra indicating that both Nitrogen-Hydrides and Nitrogen were available at the time of the diamond formation. The ratio between N0 and NH+ defects in the diamond could be an indicative of the environment in which the diamonds were formed.
CONCLUSIONS
It is suggested that the unidentified bands observed in the nitrogen region of pre-solar and carbonado diamond IR spectra arise from substitutional NH+ defects. In the carbonado spectra, the N0 bands are also detectable, which indicates that both Nitrogen and Nitrogen mono-hydride were present at the formation of the diamond. The bands of the substitutional NH+ defect are deduced by red shifting the irradiation-induced N+ bands due to the mass of the additional Hydrogen. The six bands assigned to the NH+ defects are identified in both the pre-solar and the carbonado diamond spectra. With the new assignments, all of the nitrogen-related bands in the spectra are identified and it is shown that pre-solar and carbonado diamonds contain almost exclusively single nitrogen impurities; therefore, they can be classified as Type Ib.
ACKNOWLEDGEMENTS: The authors thank to Andriy Durigin and Subrahmanyam Venkata Garimella for the inspiring discussions and for their thoughtful comments. We also like thank to Mike Sukop for reading and commenting the manuscript. This paper benefited from the careful review of Hugh Hill and Anthony P. Jones.
7 REFERENCES
Adams N.G., Smith D. and Millar T.J. 1984. The importance of kinetically exited ions in the synthesis of interstellar molecules. Mon. Not. R. Astr. Soc. 211:857-865. Andersen A.S., Jørgensen U.G., Nicolaisen F.M., Sørensen P.G., and Glejbøl K. 1998. Spectral features of presolar diamonds in the laboratory and in carbon star atmospheres. Astron. Astrophys. 330:1080-1090. Braatz A., Ott U., Henning Th., Jager C., and Jeschke G. 2000. Infrared, ultraviolet, and electron paramagnetic resonance measurements on presolar diamonds: Implications for optical features and origin. Meteoritics & Planetary Sci. 35:75-84. Braatz A., Ott U., Henning Th., Jager C., and Jeschke G. 1999. Nitrogen configuration in presolar diamonds. Lunar and Planetary Science XXX, Abstract #1551. Cheung A. C., Rank D. M., Townes C. H., Thornton D. D., and Welch W. J. 1968. Detection of NH3 Molecules in the Interstellar Medium by Their Microwave Emission. Phys. Rev. Lett. 21:1701-1705. Crawford I.A., and Williams D.A. 1997. Detection of interstellar NH towards Zeta Ophiuchi by means of ultra-high-resolution spectroscopy. Mon. Not. R. Astrn. Soc. 291, L53-L56. Colangeli L., Mennella V., Stephens J.R., and Bussoletti E. 1994. Laboratory simulation of microdiamonds present in space. Astron. Astrophys 284:583-592. Collins A.T. 1978. Migration of nitrogen in electron-irradiated type Ib diamond. J. Phys. C: Solid State Phys. 11:L417-L422. Collinst, A.T., Daviest, G., Kandae H. and Woods, G.S. 1988. Spectroscopic study of carbon-13 synthetic diamond. J. Phys. C: Solid State Phys. 21:1363-1376. Daulton T.L., Eisenhour D.D., Bernatowicz T.J., Lewis R.S., and Buseck P. 1996. Genesis of presolar diamonds: comparative high-resolution transmission electron microscopy study of meteoritic and terrestrial nano-diamonds. Geochim. Cosmochim. Acta 60:4853-4872. Davis J. 1977. The optical properties of diamonds, In Chemistry and Physics of Carbon. eds. Philips P. and Turner P. New York: Marcel Dekker Inc. p. 1-143. de Almeida A.A., and Singh P.D. 1982. NH+ - A Candidate for Comets and Interstellar Space. Astron. Astrophys. 113:199-204. Demeny A., Garai J., Nagy G., Bajnoczi B., Nemeth T. and Drozd V., 2011. Hydrogen isotope compositions in carbonado diamond: constrains on terrestrial formation. Central European Geology, 54:51-74. Farmer C. B., and Norton R. H. 1989, A high-resolution atlas of the infrared spectrum of the sun and the earth atmosphere from space, A compilation of ATMOS spectra of the region from 650 to 4800 cm−1 (2.3 to 16 µm), Vol. I, The sun, Ed. Farmer C.B., and Norton R.H. Feldman P. D., Fournier K. B., Grinin V. P., and Zvereva A. M. 1993. The abundance of ammonia in Comet P/Halley derived from ultraviolet spectrophotometry of NH by ASTRON and IUE ApJ 404:348-355. Field, J.E. 1992. The Properties of Natural and Synthetic Diamonds. London:Academic Press
8 Garai J., Haggerty S.E., Rekhi S., and Chance M. 2006. Infrared Absorption Investigations Confirm the Extraterrestrial Origin of Carbonado-Diamonds. Astrophys. J. Lett. 653:L153- L156. Goicoechea J.R., Cernicharo J., and Caux E., ISO beyond the peaks: The 2nd ISO workshop on analytical spectroscopy. Eds. A. Salama, M.F.Kessler, K. Leech & B. Schulz. ESA-SP 456. p. 99 Hill H.G.M., d’Hendecourt L.B., Perron C. and Jones A. 1997. Infrared spectroscopy of interstellar nanodiamonds from the Orgueil meteorite. Meteorit. Planet. Sci. 32:713-718. Hill H.G.M., d’Hendecourt L.B., and Kress W., Carabatos-Nedelec C. 2000. Infrared absorption of “interstellar” nanodiamonds in the two-phonon range. In Cluster and nanostructure interfaces. Edited by P. Jena, S.N. Khanna, and B. K. Rao, World Scientific Publishing, p. 419-428. Hily-Blant et al. 2010. Nitrogen hydrides in the cold envelope of IRAS 16293-2422. A&A 521:L52. Huebner W.F., and Giguere P.T. 1980. A model of comet comae. II - Effects of solar photodissociative ionization. Astrophys. J. 238:753-762. Jones A., and d’Hendecourt L.B. 2000. Interstellar Nanodiamonds: the Carriers of Mid-Infrared Emission Bands”, 2000, A&A, 355, 1191 Jones A. 2001. The Nature of Very Small Interstellar Grains, in Galactic Structure, Stars and the Interstellar Medium. Edited by C. E. Woodward, M. D. Bicay, & J. M. Shull, ASP Conf. Series, 231, 171 Kagi H., and Fukura S. 2008. Infrared and Raman spectroscopic observations of Central African carbonado and implications for its origin. Eur. J. Mineral. 20:387-393. Kerns B., and Duncan B.F. 1972. Predictions on Finding the NH and NH2 Radicals in Interstellar Space. The Astrophysical Joural 172:331-334. Koike C., Wickramasinghe C., Kano N., Yamakoshi K., Yamamoto T., Kaito C., Kimura S, and Okuda H. 1995. The infrared spectra of diamond-like residues from the Allende meteorite. Mon. Not. R. Astron. Soc. 277:986-994. Lawson S.C. and Kanda H. 1993. An annealing study of Nickel point defects in high-pressure synthetic diamond. J. Appl. Phys. 73:3967-3973. Lawson S.C., Fisher D., Hunt D.C. and Newton M.E. 1998. On the existance of positively charged single-substitutional nitrogen in diamond. J. Phys.: Condens. Matter 10:6171-6180. Lewis R.S., Anders E., and Draine T. 1989. Properties, detectability and origin of interstellar diamonds in meteorites. Nature 339:117-121. McNamara K.M., Williams G.E., Gleason K.K., and Scruggs B.E. 1994. Identification of defects and impurities in chemical-vapor-deposited diamond through infrared spectroscopy. J. Appl. Phys. 76:2466-2472. McNamara K.M. 2003. Aggregate nitrogen in synthetic diamond. Appl. Phys. Lett. 83:1325-1327. Meier R., Wellnitz D., Kim S. J., and A’Hearn M. F. 1998, The NH and CH bands of comet C/ 1996 B2 (Hyakutake). Icarus 136:268-279.
9 Meyer D.M., and Roth K.C. 1991. Discovery of interstellar NH. The Astrophysical Journal 376:L49-L52. Mitchell G.F., Ginsburg G.L., and Kuntz P.J. 1978. A steady-state calculation of molecule abundances in interstellar clouds. Atrophys. J. Suppl. 38:39-68. Mutschke H., Dorschner J., Henning Th., Jäger C. and Ott U. 1995. Facts and Artifacts in Interstellar Diamond Spectra. Astrophys. J. Lett. 454:L157-L160. Mutschke H., Dorschner J., Henning Th., Jäger C. and Ott U. 1996. Facts and Artifacts in Interstellar Diamond Spectra, Errata. Astrophys. J. Lett. 461:L59. Persson C.M. et al. 2010. Nitrogen hydrides in interstellar gas. A&A 521:L45. Petrovsky V.A., Shiryaev A.A., Lyutoev V.P., Sukharev A.E. and Martins M. 2010. Morphology and defects of diamond grains in carbonado: clues to carbonado genesis. Eur. J. Mineral. 22:35-47. Russell S.S., Arden J.W., and Phillinger C.T. 1996. A carbon and nitrogen isotope study of diamonds from primitive chondrites. Meteoriti. Planet. Sci. 31:343-355. Samoilovitch M.I., Bezrukov G.N., Butuzov V.P., and Podol’skikh L.D. 1975. Sou. Phys.-Dokl. 19:409-410. Ozima M. and Tatsumoto M. 1997. Radiation-induced diamond crystallization: Origin of carbonados and its implication on meteorite nano-diamonds. Geochim. Cosmochim. Acta 61:369-376. Sano Y., Yokochi R., Terada K., Chaves M.L. and Ozima M. 2002. Ion probe Pb–Pb dating of carbonado, polycrystalline diamond. Precamb. Res. 133:155-168. Saslaw W.C., and Gaustad J.E. 1969. Interstellar Dust and Diamonds. Nature 221:160-162. Schmitt J. L. 1969. An Investigation of the NH Bands in Stellar Spectra. Publications of the Astronomical Society of the Pacific. 81:657-664. Swing C.T. Elvey and H.W. Babcock 1941. The Spectrum of Comet Cunningham, 1940C ApJ 94:320-343.
10 Fig. 1. Mid-infrared absorption spectra of carbonado diamond from the Central African Republic (CAR) in the C-N vibrational region (solid line) are plotted. The experimental procedure is described in Garai et al. 2006. Among the characteristic terrestrial diamond absorption bands only the substitutional N0 bands (C Centre) are present in the spectra. The assignments of the rest of the bands are still debated. For comparison the characteristic absorption spectra of Ib diamond containing substitutional N (C Centre) defects (dashed line) (Field 1992) and the spectra of Allende DM1 microdiamond (dotted line) (Lewis et al. 1989) are also shown. The image shows a carbonado from the Bangui Region, Central African Republic. The patina of the surface is a characteristic feature of carbonado diamonds.
11 12 Fig. 2. Mid-infrared absorption spectra collected from thin section of Brazilian (BR) and Central African republic (CAR) carbonado diamond are plotted (Garai et al. 2006). The spectra are an intrinsic property of the diamond because no chemical treatment was used in the preparation. The assigned vibrational regions are identified. a) The irradiation-induced N+ related bands are present but red shifted in the carbonado spectra. The observed red shift is consistent with one atomic mass unit increase of the nitrogen, which can be caused by the hydrogenation of the ionized nitrogen. b) The presence of hydrogenated nitrogen is supported by the N-H Stretch and Bending bands at around 3200 cm-1 (3.12 µm) and 1652 cm-1 (6.05 µm) respectively.
13 Table 1 Reported spectral bands for pre-solar and carbonado diamonds in cm-1and their proposed assignments.
TERRESTRIAL ALLENDE MURCHISON ORGUEIL CARBONADO Assignments to presolar and carbonado diamonds by (assignments) 1Lewis 2Koike 3Andersen 4Braatz 5Colangeli 6Mutschke 4Braatz 7Hill 8Garai 9Kagi and 10McNamara Int. This Paper et al. et al. et al. et al. et al. et al. et al. et al. et al. Fukura and ref. therein 2003 Previous Studies % 1989 1995 1998 2000 1994 1995 2000 1997 2006* 2008 11Lawson et al. 1998 3210 3115 3236 3164 (~3200) 1, 2, 3, 5, 6, 7 N-H Stretch N-H Stretch 1, 5 Aromatic C=C/C=O stretch, 2 1634 1640 1632 1612 1616 1623 1650 26 1640 C=O/N-H stretching, 3 O-H N-H Bending 1590 bend (in H2O) + 1462 3 Subst. NH ; 1465 4 C-H deformation (CH3/CH2) 1456 C-H def.(CH3/CH2) 1403 1401 1402 1, 3, 5 Interstitial N/ Subst. NH+; 1399 1420 14 1438 1361 1399 1385 C-H deformation (CH3) C-H def. (CH3) (1332) 3 1334 1344 (Subst. N) 11 - Subst. NH+
10 7 1289 1284 1282 (A aggregates) 2, 5, 6, 7 C-O/C-N Stretch chem. treat. /A cent. 3 1234 1210 1220 1220 11 1220 (C-N Stretch) 10 C-O/C-N/C-C Stretch/ (C-N0) Stretch
+ 1173 1178 1150 1175 1155 (1163) 40 Interstitial N (C-NH ) Stretch 1 1122 1122 1125 (1132) 34 1126 1130 (Subst. N) 10 C-O Stretch/ Interstitial N Subst. N0 1108 1108 1109 1100 100 1100 4 C-O Stretch Subst. NH+
4 4 1090 1080 1090 1084 1084 1090 1088 1072 C-O(H), CF2 chem. treatment 1028 1054 1030 45 Subst. NH+ 909 72 Subst. NH+
*The numbers represent the averages of the bands from the three spectra. The numbers in parentheses relates to bands observed in two of the spectra.
Table 2 The irradiation induced N+ bands are red shifted by adding one atomic unit to the mass of Nitrogen, due to the mass of the additional Hydrogen. The red shifts were calculated using simple force constant model.
Assignment Frequency (cm-1) C-N+ C-NH+ 950 (10.53 µm) 935 (10.70 µm) 1046 (9.56 µm) 1030 (9.71 µm) Irradiation induced Substitutional N+ 1115 (8.97 µm) 1098 (9.11 µm) + (C -centre) 1450 (6.90 µm) 1428 (7.00 µm) 1502 (6.66 µm) 1479 (6.76 µm)
14