7412
J . Phys. Chem. 1993,97, 7412-7416
ARTICLES Laser Ablated Boron Atom Reaction with Carbon Disulfide. Infrared Spectrum of SBCS in Solid Argon and ab Initio Geometry and Frequency Calculations for Possible Products Parviz Hassanzadebt and Lester Andrews' Department of Chemistry, University of Virginia, Charlottesville, Virginia 22901
Randall Dean Davy Department of Chemistry, Liberty University, Lynchberg, Virginia 24506 Received: October 20, 1992
Codeposition of laser ablated boron atoms with a mixture of carbon disulfide in argon produced SBCS with absorption bands at 1201.9 and 1226.8 cm-l for llB and 1°B, respectively. Carbon-13 substitution shifted these bands to 1188.2 and 1210.3 cm-l. Sulfur-34 isotopic counterparts were observed at 1192.7 and 1217.6 cm-l and scrambled isotopic sulfur revealed intermediate new bands a t 1197.2.1222.8, and 1221.8 cm-1, respectively. Ab initio calculations of isotopic frequencies confirmed the identification of the SBCS insertion product.
A
Introduction Pulsed laser evaporated boron atoms have been shown to undergo insertion reactions with 0 ~ ~ 0C02, 3 , and SO2 in matrixisolation studies.14 In the case of C02 the insertion reaction required activationenergy, but the B insertionwith SO2 proceeded at 25 K in solid The present study with CS2 was performed to explore the reactivity of boron and carbon disulfide and to characterize the product by infrared spectroscopy and ab initio calculations. Experimental Section The vacuum system and chamber for matrix-isolation studies have been described previously.1.s A closed-cycle refrigerator (CTI Cryogenics, Model 22) and an indicator/controller were used to cool and monitor the temperature of the CsI window. FTIR spectra were recorded on a Nicolet 5DXB instrument at 2-cm-I resolution with an accuracy of 0.5 cm-1 and on a Nicolet 60SXR instrument at 0.5-cm-1 resolution with an accuracy of 0.1 cm-l. FTIR spectra were recorded before and after annealing and photolysis with a 175-W (Philips) medium pressure mercury arc. The first harmonic (1064 nm) of a Q-switched Nd:YAG (Quanta-Ray DCR-11) laser was focused on the boron target to generate atomic boron. The boron target was rotated at 1 rpm. Typically a laser power of about 40 mJ/pulse at the target with a pulse duration of about 5-10 ns gave sufficient boron atoms for infrared spectra of reaction products. Boron with natural abundance llB (80.2%) and loB (19.8%) (AldrichChemical Co.), enriched boron- lomaterial with 93.78% 1°B (Eagle-Pitcher Inc.), carbon disulfide (Mallinckrodt, analytical reagent), carbon disulfide with 90% enriched sulfur-34 (EG&G Mound Applied Technologies), and carbon disulfide with 99% enriched carbon13 (Cambridge Isotope Laboratories) were used as received. Carbonyl sulfide (OCS) (Matheson) was purified by condensation and vacuum distillation at 77 K. Results
B + C S 2 . A 11400 mixture of CSZ/Ar was deposited with boron atoms produced by laser evaporation of elemental boron Present addrws: Department of Chemistry, College of Sciences, Shiraz University, Shiraz, Iran.
0022-3654/93/2097-7412$04.00/0
A
cs
1400
%,
ri
1300
1200
1 100
loo0
Wavenumber
Figure 1. Infraredspcctrain the 1000-1400-cr1-~region for codeposition of CSz/Ar (1/200) with laser ablated boron. (a) Natural isotopic boron and CSz/Ar,(b) spcctruma after annealing to 30 K,and (c) 94Rjenrichcd
isotopic boron-10 with CSz/Ar.
with a laser power of about 40 mJ/pulse at the target. Sharp carbon monosulfide absorption bands at 1275.3 and 1270.1 cm-1 (labeled CS)6 and new absorptions at 1226.8, 1221.8, 1201.9, and 1197.1 cm-1 (labeled A) were observed after 2 h of sample deposition (Figure la). The relativeintensity of the 1226.8- and 1221.8-cm-1 bands to the 1201.9- and 1197.1-cm-1 bands was 1 /4 and remained constant on longer deposition. Three other sharp, weak new bands were observed: a BS band split at 1166.5 0 1993 American Chemical Society
The Journal of Physical Chemistry, Vol. 97, No. 29, 1993 7413
Boron Atom Reaction with Carbon Disulfide 1
I280 1580
1/60
1440
1420
1o;O
1180
1160
W avenumber Figure 2. Infrared spectra in the 1280-1160-cm-1region for codeposition of CS2/Ar (1/200) with laser ablated boron. (a) Natural isotopic boron and CSZ/Ar, (b) 94%enriched isotopic boron-10 with CSZ/Ar, and (c)
natural boron and 99% carbon-13 enriched CS2.
and 1162.7cm-lYa114doubletat 1078.4and 1058.3cm-l (labeled B), and a BS2 band at 1015.7 ~ m - l . ~ *Annealing * at 20 and 30 K caused the intensities of all the product bands to increase by 30% and those of the CS and BS bands to decrease by the same amount; however, the relative intensities did not change. All bands decreased on annealing at 40 K. The CS absorptions decreased in favor of a 1280-cm-l band assigned to (CS)2 by Bohn et a1.6 The increase in A absorptions on annealing was not observed in the experiments where the CS and BS bands were weak. Photolysis with the full radiation of the mercury arc lamp (254 nm) did not affect the spectrum. In other experiments the laser power was increased to 50 and 60 mJ/pulse at the target; the product bands were more intense, but no new band was observed. Increasing the CS2/Ar ratio to 1/100 caused the relative intensities of the new bands at 1226.8, 1221.8, 1201.9, and 1197.1 cm-1 of the CS absorption bands to increase by a factor of 2, and no new absorption was observed. In another experiment a 11100 mixture of CS2/Ar was passed through a 6-mm quartz tube subjected to tesla coil discharge and codeposited with boron atoms. The CS absorption bands were increased by a factor of 3; however, the 1227-, 1222-, 1202-, and 1197-cm-1bands were decreased by a factor of 2, and the intensities of these bands became comparable with those observed with the 11400 mixture of CS2/Ar. Additional bands due to C& and C3S2 were observed as described in previous experimenh6 Isotopic Substitution. Isotopic data were obtained for the new bands using a laser power of 40 mJ/pulse at the target and 11400 mixtures of CS2/Ar. With 93% enriched boron-10, the 1226.8and 1221.8-cm-1 bands were the major products and the 1201.9and 1197.1-cm-1bandintensitieswerereducedto6%ofthe 1226.8and 1221.8-cm-1bands (Figure ICand 2b); sharp l0BS (1208.9 cm-I), species B (1078.4 cm-I), and IOBS2 (1057.9 cm-1) bands
1260
1240
1220
1200
lis0
iiao
Wavenumber
Figure 3. Infrared spectra in the 1280-1160-cm-l region for codeposition for CS2/Ar (1/200) with laser ablated boron. (a) Natural isotopicboron and CSZ/Ar, (b) natural isotopic boron and a 3/2 mixture of ( 2 3 % ~ and C34S2,and (c) natural boron and a 4/5/3 mixture of 32SC32S, 32SC34S,
and 34SC34S. were also observed. In a similar experiment, natural boron was reacted with a mixture of CS2/Ar with 99% enriched carbon-13, and new bands were observed at 1210.3, 1204.6, 1188.2, and 1183.1 cm-l (Figure 2c). The relative intensities of the 1210.3and 1204.6- to 1188.2- and 1183.1-cm-' bands were 114; the llBS band and a sharp new 1044.6-cm-1band were also observed. When this experiment was repeated with 93% enriched boron10, the 1210.3- and 1204.6-cm-' bands were predominant, while the 1188.2- and 1183.1-cm-l bands decreased to 6%of the 1210.3and 1204.6-cm-l bands, and a sharp new band appeared at 1062.2 cm-1. When natural boron was reacted with a 312 mixture of C32S2 and C34S2,all the bands showed doublet patterns, as illustrated in Figure 3b. A sample of 32SC32S,32SC34S, and 34SC34S was prepared by applying a tesla coil discharge to the 312 isotopic mixture for a few minutes and then diluting with argon. Infrared spectra of this mixture revealed absorptions at 1528.2 (32SC32S), 1524.6 (3zSC34S),and 1521.1(34SC34S)cm-l with 41513 relative intensities, respectively. A similar intensity pattern was observed at 1478.3 (32S13C32S), 1474.8 (32S13C34S), and 1471.2 (34S13C3'5) cm-l. When this mixture was deposited with laser evaporated boron, bands were observed at 1201.9, 1197.2, and 1192.7 cm-1 for boron-11 and 1226.8, 1222.8, 1221.8, and 1217.6 cm-1 for boron-10 with 411 relative intensity, respectively (Figure 3c). The relative intensities of the bandsfor boron-11 are 21211 and for boron-10 are 211 11 11. Isotopic data are collected in Table I. In another experiment the boron target was enclosed inside a coaxial 112-in. tube and the CS2/Ar was passed through the tube and over the target during laser ablation. The CS and 1226.8-, 1221.8-, 1201.9-, and 1197.1-cm-l band intensities were all enhanced by a factor of 5 compared to the separate deposition of the CS2/Ar sample.
7414 The Journal of Physical Chemistry, Vol. 97, No. 29, 1993
TABLE I: Infrared Absorption Bands (cm-I) Observed from Codeposition of Laser Ablated Boron with Carbon Disulfide in an Argon Matrix at 12 K band,@cm-I band,' cm-' SBCS
32-11-12-32 32-10-12-32 32-11-13-32 32-10-13-32 34-11-12-34
1201.9 (1197.1) 1226.8(1221.8) 1188.2 (1183.1) 1210.3 (1204.6) 1192.7 (1188.1)
12-32 13-32
1275.3(1270.1) 1239.3 (1234.8)
11-32 10-32
1166.5(1162.7) 1208.9
32-11-32
1015.7
34-10-12-34 32-11-12-34 34-10-12-32 34-11-12-32 32-10-12-34
1217.6 (1215.0) 1197.2 1222.8 1197.2 1221.8
12-34
1265.1(1261.2)
11-34
1160 (1154.8)
cs
SBS 32-10-32
1057.9
Species B
@
11-32-13-32 1044.6 10-32-13-32 1062.2
The values in parentheses are due to matrix sites.
TABLE Ik Total Electronic Energy (hartrees) for BCS, SBCS, SBCO,and SCBO in Different States at the UHF and ROHF Levels of Theow UHF((SZ))@ ROHF BCS (doublet) BCS (quartet) SBCS (doublet) SBCS (quartet) SBCO (doublet) SBCO (quartet) SCBO (doublet) SCBO (quartet)
-459.900 84 (1.791) -459.939 46 (3.824) -857.55006 (1.144) -857.500 62 (3.809) -534.923 01 (0.767) -534.826 09 (3.827) -534.939 22 (1.148) -534.849 99 (3.794)
-459.88945 -459.92905 -857.541 43 -851.486 36 -534.91747 not converged -534.928 78 -534.868 00
The values in parentheses are the eigenvalues for s2 which show the extent of spin contamination for the unrestricted Hartree-Fock calcu@
lations.
+
B S. One experiment involved codepositing natural boron atoms with the effluent from an argon/sulfur di~charge.~ The spectrum revealed SSand S d at 679.9 and 676.1 cm-l and 662.1 and 642.7 cm-I, as described previously, and weak bands due to CS at 1275.3 cm-1 and NS2 at 1225.5 cm-l.10 A strong S20 band at 1157.3 cm-1 with a 1167-cm-1 shoulder was also observed. In addition a sharp 1/4 doublet was observed at 1057.9 and 1015.7 cm-1. Annealing increased the latter doublet by 50% with little effect on the other absorptions. B OCS. Similar experimentswere carried out with a 1/200 mixture of OCS/Ar with ]OB and llB, The spectra after 5 h showed a new band at 2007.3cm-l in the case of the B- 10 isotope, whichbelongstoBCO.ll TheCSabsorptions(1275.3and 1270.1 cm-I) and the bands observed from the deposition of boron with CS2/Ar were not detected. The strong absorption of 012CS (2050.1 cm-1) and O W S (1997.2 cm-l) did not allow inspection ofthe11BCOband(2002.3cm-1); however,aweakbandat 1952.2 cm-1 due to 11B13C0was detected. The 2138.2-cm-1 band of CO was increased by a factor of 10 from the CO impurity of the OCS/Ar sample. Ab Initio Calculations. Electronic structure calculationswere performed for the possible reaction products of laser evaporated boron with CS2 and OCS molecules. Unrestricted and restricted open shell Hartree-Fockcalculations were used for doublet, triplet, and quartet states with a DZP basis set12 using the HONDO-7.0 program and an IBM 3090 computer.13 Electronic energies for BCS, SBCS, SBCO, and SCBO are collected in Table 11. Vibrational frequencies and intensities were also calculated in the double harmonic approximationusing the DZP basis sets for the optimized structures. The bond lengths and bond angles for
+
TABLE IIk Ab Initio Calculated Structures, Frequencies, and Infrared Intensities for Different BCS Isotopes at the Optimized Geometry ROHF, S = 1.5, BCS (ground state), B-c = 1.4001A,C S = 1.5521A, LSBC 180°,E u = 459.92905bartrees frequency (intensity) B-cs 11-12-32 1735.7 (7.6) 926.4(1.5) 416.4(0.09) 416.4 (0.09) 10-12-32 1757.3 (7.4) 950.7 (1.7) 420.8(0.09) 420.8(0.09) 11-13-32 1688.1 (7.0) 923.4 (1.5) 404.6(0.08) 404.6(0.08) 10-13-32 1710.8(6.8) 946.8(1.7) 409.2 (0.09) 409.2(0.09) 11-12-34 1733.2(7.5) 916.2(1.5) 415.6(0.09) 415.6(0.09) 10-12-34 1755.0(7.3) 940.5(1.6) 420.1 (0.09) 420.1(0.09)
In cm-1. b In km/mol.
BS
11-32-12-32 1058.3 10-32-12-32 1078.4 11-34-12-34 1050.2
Hassanzadeh et ai.
the optimized geometry and the vibrational frequencies and intensities for isotopic substituted species are collected in Tables 111-VI. Additional theoretical studies were carried out at the selfconsistent field (SCF) level and the configuration interaction including all singles and doubles (CISD) level. The basis set was the DZP basis of Dunning and Huzinagal*(one set of polarization functions with exponents of B, 0.700; C, 0.750; S,0.700) using the PSI program ~ystem.1~ The structures were optimized by analytical gradient methods. Vibrational frequencies were obtained analytically for SCF results and by finite differenceof first derivatives for CISD results. Three structures were considered: the insertion product SBCS and two addition products, open chain BSCS and the three-membered ring n
containing structure BSCS. The results are summarized in Table VII. The lowest energy structure is the 2A' state of the insertion product SBCS. The next highest is the 2A' state of n
BSCS at +45.6 kcal/mol (CISD) relative to SBCS. The highest is the open chain BSCS at +87.3 kcal/mol (CISD) relative to SBCS. Theoretical vibrational frequencies were calculated for these isomers, and only the values for the SBCS species matched experimental results. BCS. The total electronic energiesand the eigenvalues for SZ (indicative of spin contamination) for doublet and quartet states of the BCS molecule are compared in Table 11. The doublet BCS shows high spin contamination at the UHF level. Comparison of the total eiectronicenergies at the ROHF level clearly shows that the quartet state is 24.8 kcal/mol more stable than the doublet state and is assigned as the ground state of the BCS molecule. Likewise, BCO has a quartet ground state.Il Furthermore the restricted open shell Hartree-Fock calculation for the doublet state removes the degeneracy of the bending mode by slightly bending the molecule. SBCS. The total electronic energies and the eigenvalues for S2for doublet and quartet states of the SBCS molecule are given in Table 11. The doublet state shows high spin contamination at the UHF level. Comparison of the total electronic energies at the ROHF level predicts that the doublet state is 34.6 kcal/mol more stable than the quartet state and is the ground state of the SBCS molecule. The optimized geometry for the doublet state is slightly bent at the terminal sulfur atom, which is in contrast with the linear geometry for the quartet state. Calculations for the B + C02 system show that the insertion product is lower in energy than the addition products?Js and this is also found to be the case with the B + CS2 system. SCBO dSBCO. The doublet state of SCBO has high spin contamination, and comparison of the total electronic energies at the ROHF level predicts that the doublet state is 38.1 kcal/ mol more stable than the quartet state and is the ground state of the SCBO molecule (Table 11). The quartet state of the SBCO molecule did not converge at the ROHF level; however, the total electronic energies for the doublet state at both the UHF and ROHF levels are lower than
The Journal of Physical Chemistry, Vol. 97, No. 29, 1993 7415
Boron Atom Reaction with Carbon Disulfide
TABLE Iv: Ab Initio Calculated Structures, Frequencies, and Infrared Intensities for Different SBCS Isotopes at the Optimized Geometry ROHF, S = 0.5, SBCS (ground state), S r B = 1.6056 A, B-C = 1.4740A, C S 1 = 1.5314 A, LSlBC = 179.07569O.LBCSl = 179.1°,,??-I= -857.54143 hartrees freuuencp - - (intensitvb) . ~~~
StB-CSl 32-11-12-32 32-10-12-32 32-11-13-32 32-10-13-32 34-11-12-34 34-10-12-34 34-11-12-32 34-10-12-32 32-11- 12-34 32-10-12-34 a
~
_
1803.0 (2.1) 1837.7 (3.1) 1765.2 (2.7) 1803.2 (3.9) 1798.9 (2.1) 1833.9 (3.2) 1801.9(2.0) 1836.5 (3.1) 1800.0 (2.2) 1835.2 (3.3)
1298.3 (13.1) 1326.2 (13.2) 1283.5(12.4) 1308.3 (12.4) 1288.4 (12.9) 1316.3(12.9) 1293.4(13.0) 1321.7(13.1) 1293.4 (12.9) 1320.8(13.0)
535.9 (0.2) 549.2 (0.2) 526.3 (0.2) 539.9 (0.2) 535.3 (0.2) 548.6 (0.2) 535.6 (0.2) 548.9 (0.2) 535.6 (0.2) 548.9 (0.2)
I
507.1 (0.04) 507.8 (0.04) 506.2 (0.04) 506.9 (0.04) 493.0 (0.04) 493.6(0.04) 499.8 (0.04) 500.3 (0.04) 500.3 (0.05) 501.0 (0.04)
370.3 (0.4) 384.3(0.4) 368.0 (0.4) 382.1 (0.4) 369.6 (0.4) 383.6 (0.4) 369.6(0.4) 383.6 (0.4) 370.3 (0.4) 384.3 (0.4)
170.3 (0.05) 173.1 (0.05) 167.6(0.05) 170.2 (0.05) 168.9 (0.05) 171.8 (0.05) 169.6 (0.05) 172.5 (0.05) 169.6 (0.05) 172.4 (0.05)
96.9(0.01) 97.3 (0.01) 94.3 (0.01) 94.6 (0.01) 96.2 (0.01) 96.6(0.01) 96.7 (0.01) 97.1 (0.01) 96.5 (0.01) 96.9 (0.01)
In cm-1. b In km/mol.
TABLE V Geometry
Ab Initio Calculated Structures, Frequencies, and Infrared Intensities for Different SCBO Isotopes at the Optimized ROHF, S = 0.5, SCBO (ground state), S-C = 1.5371 A,C-B = 1.5048 A, B-0 = 1.1929A, LSCB = 152.1°,LCBO = 176.7O,E t d 2: -534.92879 hartrees
S-C-B-0 32-12-11-16 32-12-10-16 32-13-11-16 32-13-10-16
frequency (intensityb) 2218.6 (13.4) 2289.9(14.6) 2214.2(13.6) 2285.7(14.8)
1540.0(2.2) 1540.5 (2.2) 1493.9 (1.9) 1494.1 (1.9)
650.7 (0.6) 655.5 (0.6) 646.0 (0.6) 650.9(0.6)
506.3(1.6) 524.1 (1.7) 504.4(1.6) 522.3 (1.7)
447.4 (2.1) 463.2(2.3) 445.6 (2.1) 461.5 (2.3)
126.1 (0.1) 126.4(0.1) 123.3(0.1) 123.6(0.1)
66.7 (0.0007) 66.9 (0.0008) 65.2 (O.OOO9) 65.3 (0.001)
I, In cm-1. b In km/mol.
TABLE VI: Ab Initio Calculated Structures, Frequencies, and Infrared Intensities for Different SBCO Isotopes at the Optimized Geometry ROHF, S = 0.5,SBCO (ground state), S-B = 1.5942 A, B-C = 1.5387A, C-O = 1.1577 A, LSBC = 171.4O,LBCO = 142.0°,EM = 534.91747hartrees frequency (intensityb) s-B-C-O 32-11-12-16 32-10-12-16 32-11-13-16 32-10-13-16 0
2222.4 (6.7) 2225.0(6.3) 2169.7(6.3) 2172.4(5.9)
1471.6 (10.4) 1529.5(11.4) 1471.3 (10.4) 1529.1 (11.4)
583.6 (0.03) 584.7 (0.03) 574.4(0.03) 575.4(0.02)
292.9 (0.3) 304.6 (0.3) 291.9 (0.3) 303.6 (0.3)
157.0(0.4) 158.9 (0.4) 155.2 (0.4) 156.9 (0.4)
82.9 (0.09) 83.0(0.09) 81.4 (0.08) 81.5 (0.08)
In cm-1. b In km/mol.
TABLE W: Comparison of CISD and SCF Calculations for Three B + C S 2 Product Isomers CISD SCF CISD SCF S-B, A B-C,A C-S,
A
S-B, A
S-C (ring), A B-C, A -9
470.2 (0.1) 483.1 (0.1) 465.8 (0.1) 479.0(0.1)
=,A
A
CS,A
SBCS 1.607 1.604 CSBC,deg 1.464 1.473 ~BSc,deg 1.536 1.528 energy, hartreea BSCS 1.751 1.760 C S (exo), A 1.843 1.801 LBCS (exo),deg 1.501 1.509 energy, hartrea BSCS 1.851 1.877 LBSC,deg
180 180 180 180 -858.064522 -857.51643 1.584 1.587 161.7 159.1 -857.991860 -857.468023
94.9 99.3 142.2 1.718 1.719 CSCS,deg 142.7 1.564 1.563 energy, hartrees -857.925478 -857.409506
the energy of the quartet state at the UHF level, and thus, the doublet state is predicted to be the ground state of the SBCO molecule. The doublet state is about 60.9 kcal/mol (calculated from UHF-UHF) and 57.3 kcal/mol (calculated from ROHFUHF)more stable than the quartet state (Table 11). Finally, the more stable arrangement of the B OCS insertion product (SCBO) is predicted to be 7.1 kcal/mol more stable than the SBCO arrangement.
+
Discussion The new product bands will be identified, and the reactivity of CS2 with atomic boron will be considered.
BS and BS2. The split bands at 1166.5 and 1162.7 cm-1 in solid argon bracket the 1165.3-cm-l band assigned to l1BS in solid neon. The 1166.5-cm-1 band exhibited a 1OBS counterpart at 1208.9 cm-l in exact agreement with a harmonic oscillator diatomic ratio (1.0364). Furthermore, the bands showed an appropriate 34S shift for BS although the individual sites were not resolved. Of course no 13Cshift was observed. The 1165.5and 1162.7-cm-1 bands are assigned to "BS in solid argon in near agreement with the 1167.6-cm-1 gas-phaseand 1165.3-cm-1 solid neon fundamentals.' The 1/4doublet at 1057.9 and 1015.7cm-1 in the B elemental sulfur experiments is clearly due to the vibration of a single boron atom. The bands are 1.1-1.2 cm-l higher than the bands assigned to lOBS2 and 11BS2in solid neon.8 The boron isotopic ratio is exactly that expected for the v3 mode of the linear SBS molecule (1.0416), and the bands are assigned accordingly. The BS and BS2 molecules are minor products in the boron atom reaction with CS2. SpeciesA. Figure 1shows that the overwhelming major product is species A. The relative intensity of 1/4 for the major 1226.8and 1221.8-cm-1 bands to the 1201.9- and 1197.1-cm-* bands suggests that the former two bands belong to the boron-10 containing species and that the 1201.9- and 1197.1-cm-1bands belong to the boron-11 containing species. Enhancement of the 1226.8- and 1221.8-cm-l bands compared to the 1201.9- and 1197.1-cm-l bands by a ratio of 93/7 with the 93% enriched boron-10 isotope clearly confirms this assignment. The relative intensity of 1/4 and the enhancement of the upper bands to the
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7416 The Journal of Physical Chemistry, Vol. 97, No. 29, 1993
lower bands by 93/7 were alsoobserved for thereactionof natural boron and 93% enriched boron- 10 with sulfur-34 and carbon-13. The bands at 1221.8 and 1197.1 cm-1 show similar isotopic ratios to those of the 1226.8- and 1201.9-cm-1 bands; thus, the former bands are identified as matrix sites of the latter bands. Similarly,carbon monosulfide showed matrix sites at 1275.3 and 1270.1 cm-I. These bands show sulfur and carbon isotopic shifts indicative of involvement of sulfur and carbon atoms. The doublet pattern with mixed isotopic carbon suggests that only one carbon atom is involved in species A. Appearance of a new band at 1197.2 cm-1 halfway between the 1201.9-cm-1 band for the all sulfur-32 isotope and the 1192.7-cm-l band for the all sulfur-34 isotope with boron- 11 and similarly the 1222.8- and 1221.8-cm-1 bands sandwiched between the 1226.8- and 1217.6-cm-1 bands with boron-10 are proof for involvement of more than one surfur atom in this species. Subtractionof the spectraobtainedfrom scrambled sulfur isotopes and mixed sulfur isotopes clearly shows the formation of the new bands as opposed to the matrix sites. The relative intensities of the 1201.9-, 1197.2-, and 1192.7-cm-1 boron-11 (and 1226.8-, 1222.8-, 1221.8-,and 1217.6-cm-1 boron-IO) bands are ingeneral agreement with the thoseobserved for theprecursorabsorptions. Ab initio frequency calculationspredict strong absorptionsfor possible products of the B CS2 reaction. The triatomic BCS molecule is calculated to absorb strongly at 1736 cm-1; scaling by0.90-0.93predictsanabsorptioninthe 1560-1610-~m-~ region which is not observed here. The BSCS addition product has an SCF calculated terminal C-S stretching mode at 1337.4 cm-l without a boron isotopic shift,which clearly does not match the observed bands. The strongest SBCS insertion product absorption is calculated at 1298.3 cm-1; scaling by 0.926 gives the observed 1201.9-cm-l band. The six calculated pure isotopic frequencies scale to the observed values with scale factors in the 0.925-0.926 range. This match of experimental and ab initio calculated isotopic shifts confirms the identification of SBCS. Note that ab initio frequency calculationspredict a pseudo triplet at 1298.3 (32SBC32S), 1293.4 (32SBC34S),1293.4 (34SBC32S), and 1288.4 (34SBC34S)cm-l . Accordingly, speciesA is assigned to the product of the insertion reaction of B with CS2. An increase in the SBCS absorption and a decrease in the CS and BS absorptionon annealingin the experimentswith relatively large amounts of CS and BS suggest that SBCS may also be formed from the CS BS recombination. The strong 1201.9-cm-l band exhibits a 10/11 isotopic ratio 1226.8/1201.9 = 1.0207, which is less than the 10/11 ratio for the BS diatomic. The 1201.9-cm-1 band likewise shows a 12/ 13 isotopic ratio 1201.9/1188.2 = 1.0115 that is less than that of the CS diatomic. The 32/34 ratio 1201.9/1192.7 = 1.0077 is comparable to ratios for both diatomics. Clearly the normal mode involves an antisymmetric stretching vibration of S-B and C S bonds in the SBCS molecule.
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Species B. The minor species B bands cannot be definitively identified. The isotopic ratios are nearly the same as those for species A, so similar normal modes are involved. It is suggested that species B is probably due to the dimer of the major SBCS insertion product in possibly a ring structurewith exocyclic> C S bonds. OCS B. The presence of BCO and the absence of CS and the 1202.2- and 1227.3-cm-1 bands indicates that OCS breaks mainly at the C-S bond to give CO and S which react with boron to produce BCO and BS. However, the BS fundamental band (1165.3 cm-1) compared to the BCO band is too weak to be observed. Absence of the CS absorption band and any new band in the CS and BO stretching regions also indicate that OCS does not break through the C-O bond and that B does not react to form OBCS or OCBS in the B OCS experiments.
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Conclusions The major product of the reaction of B atoms and CSZis the SBCS insertion product. Like C02 but unlike SO2, the CS2 reaction requires activation energy which can be provided by hyperthermal boron atoms from laser ablation. The SBCS insertion product was identified from isotopic shifts at all isotopic positions and ab initio calculations of isotopicfrequencies. Further ab initio calculations show that the insertion product is more stable than a three-membered ring structure and the addition product.
Acknowledgment. We gratefully acknowledgefinancial support from the National Science Foundation Grant CHE 91-22556. References and Notes Burkholder, T.; Andrews, L. J. Chem. Phys. 1991, 95, 8697. Burkholder, T.; Andrews, L. Unpublished data. Burkholder, T.; Andrews, L.; Bartlett, R. J. J. Phys. Chem. 1993.97, Burkholder, T.; Andrews, L. Chem. Phys. Lett. 1992, 199, 455. Hassanzadeh, P.; Andrews, L. J. Phys. Chem. 1992, 96, 9177. Bohn, R.; Hannachi, Y.;Andrews, L. J . Am. Chem. Soc. 1992,114, Brom, J. M., Jr.; Weltner, W., Jr. J. Chem. Phys. 1972, 57, 3379. Brom. J. M.. Jr.: Weltner. W.. Jr. J. Mol. Soecfrosc. 1973.45. 82. (9) Hasknzadeh, P.; Andrews, L. J. Phys. Chem. 1992, 96, 6579. Brabson, G. D.; Mielke, 2.;Andrews, L. J. Phys. Chem. 1991, 95, 79. (10) Hassanzadeh, P.; Andrews, L. J. Am. Chem. Soc. 1992, 114, 83. (11) Hamrick, Y.M.; Van Zee, R. J.; Godbout, J. T.; Weltner, W., Jr.; Lauderdale, W. J.; Stanton, J. F.; Bartlett, R. J. J . Phys. Chem. 1991, 95, 2840; 1991, 95, 5366. (12) Huzinaga, S.J . Chem. Phys. 1965, 42, 1293. Dunning, T. H. J . Chem. Phys. 1970.53, 2823. (13) Dupuis,M.;Rhys,J.;King,H. F.J. Chem.Phys. 1976,65,11. Dupuis, M.; Watts, J. D.; Villar, H. 0.;Hurst,G. J. B. Comput. Phys. Commun. 1989, 52, 415. (14) PSI, Distributed by PSI-TECH, Watkinsville, GA 30606. ( 15) Marshall, P.; O'Connor, P. B.; Chan, W. T.; Khristof, P. V.; Goddard, J. D. In Gas-Phase Metal Reactions; Fontijin, A., Eds.; Elsvier: Amsterdam, 1992.
