The 3500 Å 1A2-1A1 transition of formaldehyde-h2 d2 and hd

Abstract

Interactions of vibrations through rotation about the principal axes of the molecule, and anharmonic resonance interactions were found to explain satisfactorily almost all the rotational level perturbations observed in the vibronic states of the H2CO, D2CO, and HDCO molecules. The basis for these explanations was found in model calculations for perturbations in vibrotors of asymmetries and inertial parameters appropriate for formaldehydes. The most important result that emerged is that it can be difficult to distinguish a-axis Coriolis and Fermi resonances, and b- and c-axis Coriolis resonances from each other unless intensity as well as energy perturbations are analyzed. Strong coupling of the levels ν4 and ν6 in the ground state of HDCO, through rotation about the a-axis was analyzed exactly to determine the inertial constants of the two states, the coupling parameter and the difference in vibrational energy levels. There is appended a set of graphs which make it possible to estimate for a given a-axis Coriolis resonance in an asymmetric rotor whether the relatively simple symmetric top energy expression will be adequate for band analysis.