Ab initio calculation of anharmonic vibrational spectra of hydrazine and hydrazine-d4

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 Mphiller-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 v(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. (C) 2003 Elsevier Science B.V. All rights reserved.