Half-projected Hartree-Fock calculations for the spectroscopic parameters, frequencies, and intensities of the torsional mode of the lowest lying singlet excited states of hydrogen peroxide

Abstract

Quantum chemical calculations have been performed in half-projected Hartree–Fock (HPHF) and CIS approaches for estimating the energy levels of the lowest two excited states of hydrogen peroxide. Geometry optimization was performed for the respective states at the equilibrium configuration with an elaborate quadrupole-zeta basis set augmented with polarization and diffuse functions. The model of the nonrigid rotor in an anharmonic potential was used for calculating the frequencies and intensities of the torsional mode, and the spectroscopic parameters were evaluated with a view to understand more closely the vibrational structure associated with the experimental ultraviolet (UV) spectrum of this molecule. While the spectroscopic parameters are new, reasonably good agreement is achieved for the frequencies of the torsional mode with the existing theoretical and experimental data for the 11B state. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 75: 631–636, 1999