Ab initio calculation of anharmonic vibrational spectra of hydrazine and hydrazine-d 4

Abstract

Anharmonic vibrational spectra of gauche conformers of hydrazine and hydrazine-d 4 were studied using vibrational self-consistent field (VSCF) and correlation-corrected vibrational self-consistent field (CC-VSCF) methods within second order Møller–Plesset perturbation theory (MP2). Wavenumbers and intensities of both fundamental and overtone transitions were computed in TZV(d,p) and TZV(2d,2p) basis sets. Anharmonic spectra calculated on MP2/TZV(2d,2p) potential energy surface are in much better agreement with the experiment than those obtained in TZV(d,p) basis, but the energy sequence of ν(N–H) stretching modes is preserved in both basis sets. CC-VSCF computed wavenumber of the torsional mode overestimates its experimental position by 80 and 34 cm −1 in TZV(d,p) and TZV(2d,2p) basis sets, respectively. The anharmonic spectrum of hydrazine-d 4 computed at the same level of theory also provides adequate description of the experimental data, with the position of torsional vibration 9 cm −1 above the observed one.