Infrared and raman spectra of C4H4Se and C 4D4se isotopomers: A DFT-PT2 anharmonic study

Ir and raman spectra of selenophene and of its perdeuterated isotopomer have been obtained in gas phase through density-functional theory (dft) computations. vibrational wavenumbers have been calculated using harmonic and anharmonic second-order perturbation theory (pt2) procedures with the b3lyp method and the 6-311 g** basis set. anharmonic overtones have been determined by means of the pt2 method. the introduction of anharmonic terms decreases the harmonic wavenumbers,giving a significantly better agreement with the experimental data. the most significant anharmonic effects occur for the c-h and c-d stretching modes,the observed h/d isotopic wavenumber redshifts being satisfactorily reproduced by the pt2 computations within 6-20 cm -1 (1-3%). in the spectral region between 500 cm-1 and 1500 cm-1,the ir spectra are dominated by the out-of-plane c-h (c-d) bending transition,whereas the raman spectra are mainly characterized by a strong peak mainly attributed to the c=c + c-c bonds stretching vibration with the contribution of the in-plane c-h (c-d) bending deformation. the current results confirm that the pt2 approach combined with the b3lyp/6-311 g level of calculation is a satisfactory choice for predicting vibrational spectra of cyclic molecules. © 2013 andrea alparone.