[Infrared, Raman and density functional study of vibration spectra of 2, 3-dichloropyrazine]

Fourier transform infrared (FTIR) spectra of 2,3-dichloropyrazine in the region 400-4000 cm(-1) were measured under solid state condition using KBr pellets method and liquid state by the melting method, besides, a Fourier transform Raman (FT-Raman) spectra in region 600-4 000 cm(-1) was recorded. Then equilibrium geometry of 2,3-DCP was optimized, and based on this, the harmonic vibrational frequencies, infrared intensities and Raman activities were calculated using B3LYP method of the density function theory (DFT) in conjunction with 6-311++G(2df, 2pd) basis set, furthermore, a comprehensive anharmonic calculation was also been performed for obtaining more accurate vibrational frequencies using second-order perturbation theory treatment based on quadratic, cubic and quartic force constants. Infrared and Raman spectra were simulated corresponding to theory. Experimental FTIR and FT-Raman bands were compared with those positions of peaks obtained from anharmonic calculations and intensities or activities from harmonic carefully. Each vibrational band was assigned and interpreted in detail with help of potential energy distribution (PED) for the first time. In addition, it was shown that anharmonic results exactly reproduced to experimental data, improved the validity of prediction greatly in vibration frequencies, discrepancies between anharmonic and experimental results were limited to below 10 cm(-1) in most of vibrational bands, even if in the high energy regions, which have a poor performance for hanmonic calculation, and these differences would be decreased to lower than 19 cm(-1). It is extremely helpful for assigning and predicting vibrational spectra. Present conclusion can be expanded to others molecular systems.