Spectra and structure of silicon‐containing compounds. XXXVI—Raman and infrared spectra, conformational stability, ab initio calculations and vibrational assignment of ethyldibromosilane

Abstract

The Raman spectrum of liquid ethyldibromosilane, CH 3 CH 2 SiHBr 2 , was recorded at various temperatures between 298 and 218 K, and the spectrum of the crystal was obtained at 210 K from a sample sealed in a capillary. Additional spectra of the amorphous and annealed crystals, which were deposited on a copper finger cooled with boiling liquid nitrogen, were recorded. The infrared spectra were recorded of the vapor and amorphous and crystalline solid in the range 4000-50 cm −1 and mid-infrared spectra isolated at 4.8 K in argon and nitrogen matrices were also observed. These vibrational spectra show that two conformers, anti and gauche, are present in the vapor and in the liquid, but only the anti conformer remains in the crystalline solid. Three conformer pairs in the Raman spectrum of the liquid phase were used to obtain the enthalpy difference, which gave an average value of 128 ± 17 cm −1 (1.53 ± 0.2 kJ mol −1 ) with the anti form lower in energy. At ambient temperature it is estimated that there is 52 ± 2% of the gauche conformer present in the liquid. The optimized geometries, infrared and Raman intensities, and scaled vibrational wavenumbers for the anti and gauche conformers were obtained from ab initio MP2/6-31G(d) calculations with full electron correlation. The conformational energy difference was also obtained from ab initio MP2/6-311 + G(d,p) calculations which gave a predicted energy difference of 97 cm −1 with the anti form the conformer of lower energy. These spectroscopic and theoretical results are discussed and compared with the corresponding quantities for some similar molecules.

Vibrational study of thiophene and its solvation in two polar solvents, DMSO and methanol by Raman spectroscopy combined with ab initio and DFT calculations

“…The Raman scattering cross section, or/oX, which are proportional to Raman intensities may be calculated from the Raman scattering amplitude and predicted wavenumbers for each normal modes using the relationship [43][44]:…”

Understanding excited-state structure in metal polypyridyl complexes using resonance Raman excitation profiles, time-resolved resonance Raman spectroscopy and density functional theory

“…This parameter may be related to the observed Raman intensity in terms of the differential scattering cross-section as given in Eq. (5) [56] assuming that all appropriate experimental biases have been accounted for.…”

“…Some care is required in dealing with intensity outputs from programmes such as Gaussian [52]. The IR intensities are relatively straightforward-they are related to the square of the dipole moment change with respect to Q, the relevant normal coordinate [53][54][55][56]; however, the Raman activities reported in the Gaussian output are not directly related to the observed differential Raman cross-sections ∂ j /∂˝, i.e. the observed signal intensities.…”

Synthesis, structural and optical properties of a novel bilayered organic–inorganic perovskite C5Pb2I5

“…2 shows the Raman bands due to internal vibration modes of the organic cations. The assignment of these bands is based on previous works [28][29][30][31] and on calculations of the vibration eigenvectors performed using the ab-initio PM3 method [32,33]. The Raman bands due to bending vibrations of the organic skeleton occur between 350 and 550 cm À 1 .…”