Coriolis induced vibration and rotation mixing in formaldehyde

Abstract

The effect of Coriolis interaction on the intramolecular dynamics of formaldehyde is investigated theoretically. Classical dynamics calculations are presented that include all seven degrees of freedom, i.e., the six vibrational modes and the rotational mode associated with K, the projection of total angular momentum on a body-fixed axis. These calculations show that vibrational modes 4 (out of plane bend) and 6 (HCO bend) can be significantly coupled due to Coriolis interaction. The qualitative features of such coupling is further understood via study of a reduced dimension model that includes just modes 4, 6, and the rotational degree of freedom. Two interesting classical consequences of Coriolis interaction are noted. First, for large K (e.g., for ‖K‖∼J) we find vibrational mixing can occur without significant deterioration of K. We find that this mixing is not due to the usual ‘‘Chirikov’’ or pendulum picture of nonlinear resonance. Second, we find that both vibrational and rotational mixing can occur when the rotational frequency is in resonance with the difference in vibrational frequencies. In this situation, the resonances lead to a partial K mixing. Chaos about the resonances can lead to a more extensive K mixing. Quantum calculations are also performed for the reduced dimension model and the nature of the quantum eigenstates is discussed in relation to the corresponding classical dynamics.