J . Phys. Chem. 1992,96, 1582-1589
1582
Reaction of Atomic Hydrogen and Carbon Disulfide. Infrared Spectra of HSCS and HSHCS in Solid Argon Robert B. Bohn, G. Dana Brabson, and Lester Andrews* Chemistry Department, University of Virginia, McCormick Road, Charlottesville, Virginia 22901 (Received: August 8, 1991)
Matrix infrared spectroscopy has been used to characterize the cocondensation reaction products of H atoms and CS2in solid argon at 12 K. The major product bands at 1275.2 and 1227.8 cm-l were characterized by photolysis with 320-1000-nm radiation and reappearance on annealing to 18 K to allow diffusion and reaction of trapped H atoms. Deuterium, 13C,and 34Sisotopic data were used to identify the major product as the HSCS radical. Vibrational frequencies calculated at the DZP level for the trans conformer are in excellent agreement with the observed spectrum. A most striking feature in the spectrum is the intensification of the 2uc-s mode due to Fermi resonance with the Y~ fundamental. Minor product bands at 1082 and 1059 cm-l increased on 320-1000-nm photolysis, disappeared on 220-1000-nm irradiation, and did not reappear on final sample annealing. DZP calculations support assignment of these bands to cis- and trans-dithioformic acid, respectively.
Introduction Reactions of H atoms with various systems are fundamental to our understanding of chemical dynamics especially in the combustion of hydr0carbons.l Although reaction 1 is a vital step H O + CO [HOCO] H + C02 (1)
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H2CSand HSHCS, have been studied by infrared and microwave ~pectroscopy.l~-~~ Therefore, it is the goal of these experiments to characterize new ternary H, C, and S species by matrix infrared spectroscopy.
Experimental Section Ar/CS2 mixtures with matrix/reagent (M/R) of 100/1 were in the conversion of CO into C 0 2 , the reverse reaction (-1) from prepared on a stainless steel vacuum line using standard manophotolysis of HBr in the presence of C 0 2 requires hot H atoms.z4 metric techniques. CS2 (Merck) was cooled to 77 K using liquid Wittig et al. have investigated reaction -1 with hydrogen-bonded complexes of C 0 2 prepared in a supersonic e x p a n s i ~ n . ~ - I ~ N,, and the line was evacuated to remove volatile impurities. Ar/l3CS2(Cambridge Isotope Laboratories) and Ar/C34S2(EG Photodissociation of H-X (X = Br, SH) by an ArF laser leaves & G Applied Technologies) samples were prepared in a similar behind the H-OCO fragment which then goes as reaction -1. way. Hydrogen (D2) (Matheson) samples were diluted to M/R Milligan and Jacox” photolyzed H 2 0 in a C O matrix and = 50/1 or 100/1. characterized the products of reaction 1 as cis and trans forms Figure 1 illustrates one experimental method for the reaction of HOCO. of H atoms with CS2. This 6-mm-0.d. quartz tube was bent From a chemical standpoint, it is of interest to prepare sulfur approximately 1 in from the end to eliminate irradiation of the analogues of known oxygen-containing compounds. For instance, matrix by the microwave-powered Ar/H2 discharge (Evensonthe sulfur analogues of C O and COz are well-known stable Broida cavity, Burdick MW-200 diathermy); microwave power molecules. In addition, the HCO radical occurs in the upper was maintained in the 30-40 W range to keep the discharge short atmosphere and is a very important combustion intermediate. of the bend in the tube (hereafter called a “blind” discharge). The Surprisingly, sulfur counterparts of the above radicals, HCS and Ar/CSz mixture was codeposited from a separate vacuum line HSCS, have not been observed. Various objects in the solar with the discharged Ar/H2 sample onto a CsI window maintained systemI2 (Io and comets) are abundant in hydrogen, carbon, and at 12 K by an Air Products closed-cycle helium refrigerator. Gas sulfur. Moreover, on Earth a substantial amount of coal mined deposition rates were 1-2 mmol/h each. Sample photolysis was in Illinois contains a large quantity of sulfur, which contributes performed by light from a high-pressure mercury arc (T. J. Sales, to the acid rain. It is important to know the intermediate species Inc., BH-6-1, 1000 W) passed through water and Corning glass produced in combustion-like processes involving hydrocarbons and long-wavelength pass filters (290, 320, 470 nm). The other exsulfur. perimental method employed a straight 6-mm-0.d. quartz disCH4 + 2S2 2H2S + CS2 (2) charge tube open to the condensing samples with a protruding discharge (hereafter called ‘open” discharge). Although the intermediate HCS has not been observed, ab initio Infrared spectra were recorded at 0.5 cm-’ resolution using a calculations have predicted the vibrational spectrum of HCS.I3 Nicolet 7199 spectrometer. First, 250 interferrograms of the cold The unstable formaldehyde and formic acid sulfur analogues, CsI window were collected and processed to produce a background spectrum. Second, an additional set of 250 interferrograms of (1) Lewis, B.; Elbe, G. Combustion, Flames and Explosions of Gases; the samples were collected, processed, and ratioed to the backAcademic Press: New York, 1961; p 90. ground spectrum to give a simulated double-beam spectrum. (2) Quick, C. R., Jr.; Tiee, J . J . Chem. Phys. Lerr. 1983, 100, 223.
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(3) Kleinermanns, K.; Wolfrum, J. Chem. Phys. Lert. 1984, 104, 157. (4) Kleinermanns, K.; Linnebach, E.; Wolfrum, J. J . Phys. Chem. 1985,
89, 2527.
(5) Buelow, S.; Radhakrishnan, G.; Catanzarite, J.; Wittig, C. J . Chem.
Phys. 1985, 83, 444.
(6) Radhakrishnan, G.; Buelow, S.; Wittig, C. J . Chem. Phys. 1986, 84, 727. (7) Buelow, S.; Noble, M.; Radhakrishnan, G.; Reisler, H.; Wittig, C.; Hancock, G. J . Phys. Chem. 1986, 90, 1015. (8) Buelow, S.;Radhakrishnan, G.; Wittig, C. J . Phys. Chem. 1987, 91, 5409. (9) Hausler, D.; Rice, J.; Wittig, C. J . Phys. Chem. 1987, 91, 5413. (10) Rice, J.; Hoffman, G.; Wittig, C. J . Chem. Phys. 1988, 88, 2841. ( 1 1 ) Milligan, D. E.; Jacox, M. E. J . Chem. Phys. 1971, 54, 927. (12) Nash, D. B.; Howell, R. R. Science 1989, 244, 454. (13) Goddard, J. D. Chem. Phys. Letf. 1983, 102, 224. Senekowitsch, J.; Carter, S . ; Rosmus, P.; Werner, H. J. Chem. Phys. 1990, 147, 281.
0022-3654/92/2096-1582$03.00/0
Results The reaction of discharged Ar/H2 with Ar/CS2 samples and isotopically substituted precursors will be presented. In addition, ab initio calculations of possible reaction product structures and spectra will be described. ~
~~
(14) Jacox, M. E.; Milligan, D. E. J . Mol. Spectrosc. 1975, 58, 142. (15) Turner, P. H.; Halonen, L.; Mills, I. M. J . Mol. Spectrosc. 1981.88, 402. (16) Clouthier, D. J.; Ramsey, D. A. Annu. Reu. Phys. Chem. 1983, 34, 31 ..
(17) Ioannoni, F.; Moule, D. C.; Goddard, J. D.; Clouthier, D. J. J . Mol. Srrucr. 1989, 197, 159. (18) Bak, B.; Nielsen. 0.;Svanholt, H. J . Mol. Spectrosc. 1979, 75, 134.
0 1992 American Chemical Society
The Reaction of Atomic Hydrogen and Carbon Disulfide AdCSZ
TABLE I: Infrared Absorptions ( c d ) of the Major Product Species A Formed by Codeposition of Discharged Argon/Hydrogen Mixtures with Argon/Carbon Disulfide
hv port
Arm,
The Journal of Physical Chemistry, Vol. 96, No. 4, 1992 1583
H/”C
H/”C
D/12C
D/’%
H/j4S
D/j4S
2527.5 1275.2 1227.8 941.4 627.9 412.9
2527.5 1247.1 1201.0 938.9 618.3
1805.3 1249.7 1213.1 713.8 614.8
1805.3 1225.7 1189.6 709.3 608.7
2527.7 1264.1 1211.2 939.2 617.1 412.8
1242.6 1195.9 710.8 605.2
-I
TABLE II: Infrared Absorptions (cm-I) of the Minor haduct Species B and c Formed by Codeposition of Ar/H, Mixtures with Ar/CS, Samples at 12 K
hp-wave cavity
Figure 1. Schematic representation of the matrix apparatus for addition of H atoms to CS2. Hydrogen atoms were produced by passing the
Ar/H2 mixture through a microwave discharge; the 6-mmquartz tube was bent approximately 1 in. from the end to prevent discharge radiation from reaching the matrix.
B
C
H/I2C
H/I3C
D/I2C
D/I3C
H/j4S
D/j4S
1290.5“ 1059.8 933.4 836.8 682.6 1265.4b 1082.2 925.5 807.2 725.8
1280 1037.5 925.1 828
1133.5 867 764.5 670.0 622.0 1123.4
1102.4
1289.1 1052.1 932.5 835 674.8
1128.4
B’
B” C‘ C”
H2CS
A
1255 1062.7 918.2 799.0
1091.4
776.7 655.8 613.3
1146.3 928.6 1056.5 673.9 1 139.8 938.6 1063.0 69 1
c
1118.4
1076.7 921.4 806.1
1118.1
1141.8 1049.6
1111.1
1135.5 1056.1
v1C.S) mplon
“DZP frequencies scaled by factor of 0.900 are 1320, 1050, 949, 856, and 683 cm-I. *DZP frequencies scaled by factor of 0.900 are 1300, 1080, 945, 824, and 707 cm-l. ‘Obscured by zC34S.
A
TABLE III: Infrared Absorptions (cm-I) of the Minor hoduct Species D Formed by Codeposition of Discharged Argon/Hydrogen Mixtures with Argon/Carbon Disulfide at 12 K
WSC bend
A wt.of.plan8 bnd
A
9
4 do0
lh00
1boo
800
800
400
WAVENUMBERS
Figure 2. (a) FTIR spectrum of 5 mmol of Ar/CS2 = 100/1 sample with 15 mmol of blind discharged Ar/H2 = 50/1 sample deposited on a CsI window at 12 K. (b) FTIR spectrum of the same matrix after photolysis with 320-1000-nm radiation for 1.5 h. (c) FTIR spectrum of the same matrix after annealing to 18 f 1 K for 5 min and recooling to 12 K.
+
Ar/H2 (D2) Ar/CS2. Figure 2 shows a typical spectrum recorded after the codeposition of Ar/H2 passed through a blind microwave discharge plus Ar/CS2 at 12 K. Although not presented, very strong absorptions at 1528.2 and 1478.4 cm-’ belong to I2CS2and I3CS2in their natural isotopic abundances, respectively. Figure 2a shows the spectrum after 5 h of deposition with a weak band at 2527.5 cm-l (not shown) appearing in conjunction with intense absorptions at 1275.2, 1227.8,941.4,628.4, and 412.9 cm-I labeled A. Much weaker bands were observed at 1290.5, 1059.8, and 933.4 cm-’ (species B) and 1265.4, 1082.2, and 925.5 cm-l (species C). The 1478.4-cm-’ precursor I3CS2band in natural abundance was about half again stronger than the 1275.5-cm-I product band; this means that almost 1% of the CS2reagent was
H/I2C
H/”C
D/12C
D/’)C
1252.9 1004.9
1252.3 977.9
1065.5 853.0
1034.4 850.8
H/j4S
D/34S 1062.2
999.0
converted to product assuming comparable absorption coefficients for precursor and product modes. Figure 2b illustrates the effect of 320-1000-nm radiation on the sample; species A bands were reduced by more than 90% and species C bands increased 30%. The matrix was warmed to 18 K for 5 min, and Figure 2c shows that the major product bands labeled A increased 4-fold in intensity from those of the photolyzed spectrum, but species B and C bands did not change. Substitution of D2 for H2through the blind discharge resulted in the production of five new species A absorptions at 1805.3, 1249.7, 1213.1, 713.8, and 614.8 cm-I, which parallel the above absorptions in photochemical and annealing behaviors and are listed in Table I. In addition strong new bands were observed at 1133.5 (species B) and 1123.4 cm-’(species C), which are given in Table I1 along with other bands associated by photochemical behavior. Figure 3a shows a spectrum recorded after codeposition of Ar/H2 through an open discharge with Ar/CS2. The species A bands were observed with yield comparable to those of the blind tube; however, species B bands were 400% stronger, species C bands were 200% stronger, and a strong new band was observed at 1004.9 cm-’ (species D, Table 111). Other new features included H 0 2 (1 389, 1101 cm-I), CH4 (1 306 cm-’), C3S2(1024 cm-l), CH2S (987 cm-I), and Ar,H+ (903 cm-’) absorption~.’*J~.~~ (19) Bohn, R.B.; Hannachi, Y.; Andrews, L. To be published. (20) Wight, C. A.; Ault, B. S.; Andrews, L. J . Chem. Phys. 1976,65, 1244.
1584 The Journal of Physical Chemistry, Vol. 96, No. 4, 1992
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Bohn et al.
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