Discrete variable approaches to tetratomic molecules: Part II: application to H 2O 2 and H 2CO

Abstract

We have carried out large-scale calculations for accurate vibrational energy levels of formaldehyde and hydrogen peroxide. The discrete variable representations of the radial and angular coordinates are employed together with the contraction scheme resulting from several diagonalization/truncation steps. The global potential energy surface due to Carter et al. [J. Mol. Spectrosc. 90 (1997) 729] is used for H 2CO and due to Koput et al. [J. Phys. Chem. A 102 (1998) 6325] for H 2O 2. For both molecules, the calculated vibrational energy levels are characterized by combining vibrationally averaged geometries and expectation values of rotational constants with several adiabatic projection schemes for automatic quantum number assignments. The energy levels of H 2CO involving the excited ν 2 and ν 3 vibrations appear as resonances beyond the zero-order picture consisting of uncoupled 3D stretching and 2D bending modes. The torsional energy levels of H 2O 2 are studied in great detail and different energy patterns occurring below and above the cis barrier are discussed. Our full dimensional calculations for H 2O 2 have shown that the OH triad levels, 2 ν OH, are symmetry adapted local mode states.