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Fourier transform infrared measurements on the spectra of the products of the vaporization of silicon/carbon mixtures trapped in solid argon in concert with ab initio calculations using second order many body perturbation theory have resulted in the identification for the first time of two vibrational fundamentals, 3 (b 1u )ϭ982.9 and 4 (b 2u )ϭ382.2 cm Ϫ1 , of the rhombic ground state structure of Si 2 C 2 . The observed frequencies, intensities, and isotopic shifts are in good agreement with the ab initio predictions. Tentative assignments are also made for fundamentals of the linear ͑SiCCSi͒ and distorted trapezoidal isomers. The relative energies of the three isomers have been estimated at various ab initio levels.

Fourier transform infrared observation of the ν2 stretching mode of the HCCCO radical in solid Ar J. Chem. Phys. 98, 9251 (1993); 10.1063/1.464405Fourier transform far infrared spectroscopy of the ν' 3 vibration of SiC2 in Ar at 10 K A Fourier transform infrared study of the vibrational spectrum of Si 2 C produced by vaporizing mixtures of silicon and carbon-12 or carbon-13 and quenching the products in Ar at 13 K has confirmed a previously observed vibration at 1188.4 cm -1 as the v~ (b 2 ), antisymmetric Si-C stretching mode, and resulted in the identification of a new vibration at 839.5 cm -1 as the vi'(a l ), symmetric Si-Si stretching fundamental. No bending mode has been observed; however, the identification of an absorption at 1354.8 cm -I as the v;(a l ) + V~(b2) combination band is proposed. The results are confirmed by l3C, 29Si, and 30Si isotopic data and are in excellent agreement with the predictions of ab initio calculations carried out by Rittby in collaboration with this work. Force constant adjustment calculations confirm the ground state geometry as a floppy, bent symmetrical structure.

The products of vaporization of boron/carbon mixtures around 3000 K were trapped in argon matrices at 10 K and their Fourier transform infrared spectra were measured. Analysis of the spectra combined with the predictions of density functional theory (DFT) calculations have resulted in the assignment of a previously observed vibration at 1194.4 cm−1 to the ν2 fundamental of cyclic BC2, which is effectively symmetric. The assignment is supported by 10B, 11B, and 13C isotopic data and is in good agreement with the theoretical predictions.

Articles you may be interested inElectronic structure of diatomic boron nitride Fourier transform infrared measurements on the spectra of the products of the vaporization of silicon/carbon mixtures trapped in argon at ϳ10 K combined with the results from a published ab initio study and from new theoretical calculations carried out in the present work, have resulted in the first observation of a spectrum for the pentagonal Si 3 C 2 cluster. Three vibrational fundamentals have been assigned: the 2 ͑a 1 ͒ symmetric ''breathing'' vibration at 681.1 cm Ϫ1 , the 7 ͑b 2 ͒ Si ␣ -C-C-Si ␣ stretching deformation at 956.7 cm Ϫ1 , and the 8 ͑b 2 ͒ C-Si ␤ -C antisymmetric stretching vibration at 597.8 cm Ϫ1 . The observed frequencies, relative intensities, and 13 C, 29 Si, and 30 Si isotopic shifts are in excellent agreement with the theoretical predictions.

Fourier transform infrared matrix measurements carried out in conjunction with ab initio calculations reported in a companion paper by Rittby have resulted in the first identification of two fundamental vibrations, the C=C stretching mode ν3(σu)=1955.2 cm−1, and the Si–C stretching mode ν4(σu)=898.9 cm−1, of the SiC3Si cluster formed by trapping the products of the vaporization of silicon/carbon mixtures in Ar at 10 K. The observed frequencies, relative intensities, and 13C, 29Si, and 30Si isotopic shifts for the ν3 and ν4 vibrations are in good agreement with the results of the ab initio calculations at the second-order many-body perturbation theory [MBPT(2)] level which predict a linear centrosymmetric geometry for the ground state of SiC3Si. The results of force constant adjustment calculations are consistent with the proposed vibrational assignments and structure.

A Fourier transform study of the vibrational spectrum of SiC2 produced by vaporizing mixtures of silicon and carbon-12 or carbon-13 at 2900 K and quenching the products in argon at 10 K, has enabled the identification for the first time of the ν″3(b2) vibrational mode, which the results of an earlier matrix study had suggested should lie in the far infrared. The assignment of a frequency observed at 160.4 cm−1 to the ν″3 mode is confirmed by isotopic data and supported by the predictions of ab initio calculations. Optimized force constants have been derived using the frequencies of the newly assigned mode, the previously reported, ν″1(a1)=1741.3 and ν″2(a1)=824.3 cm−1 vibrations, and their values on single and double carbon-13 substitution. Two models, cyclic and T-shaped, are discussed for the molecule, which is of C2V symmetry.

The vibrational spectrum of Si 3 C has been observed for the first time in a Fourier transform infrared study of the products of the vaporization of carbon/silicon mixtures trapped in Ar at 13 K. Five of the six fundamental modes have been assigned: the symmetric breathing vibration, VI (a l ) = 658.2 cm-I ; the Sip-Sia-Sip symmetric deformation vibration, v 2 (a l ) = 511.8 cm-I ; the Sip-C--Sip symmetric deformation vibration, v 3 (a l ) = 309.5 cm-I ; the Sip-C antisymmetric stretching vibration, v 5 (b 2 ) = 1101.4 cm-\ and the Sia-Sip antisymmetric stretching vibration, v 6 (b 2 ) = 357.6 cm -I. The assignments are supported by 13C, 29Si, and 30Si isotopic data and are in excellent agreement with the predictions of an ab initio study carried out by Rittby in collaboration with this work. The results of force constant adjustment calculations are consistent with the ground state geometry established by the ab initio calculation, a rhomboidal structure of C 2v symmetry, with carbon-silicon transannular bonding between the two equivalent Sip atoms.