The nu(6) fundamental frequency of the (A)over-tilde state of formaldehyde and Coriolis perturbations in the 3 nu(4) level

Abstract

Formaldehyde is the smallest stable organic molecule containing the carbonyl functional group and is commonly considered to be a prototype for the study of high-resolution spectroscopy of polyatomic molecules. The a-axis Coriolis interaction between the near-degenerate nu(4) and nu(6) (out-of-plane and in-plane wagging modes, respectively) of the ground electronic state has received extensive attention and is thoroughly understood. In the first excited singlet (A) over tilde (1)A(2) electronic state, the analogous Coriolis interaction does not occur, because the (A) over tilde state suffers from a pseudo-Jahn-Teller distortion, which causes a double-well potential energy structure in the q'(4) out-of-plane coordinate, and which dramatically reduces the effective nu'(4) frequency. The nu'(4) frequency is reduced by such a great extent in the (A) over tilde state that it is the 3 nu'(4) overtone which is near degenerate with nu'(6). In the current work, we report the precise nu'(6) fundamental frequency in the (A) over tilde state, and we determine the strength of the a-axis Coriolis interaction between 3 nu'(4) and nu'(6). We also provide a rotational analysis of the nu'(4) + nu'(6) combination band, which interacts with 3 nu'(4) via an additional c-axis Coriolis perturbation, and which allows us to provide a complete deperturbed fit to the 3 nu'(4) rotational structure. Knowledge of the Coriolis interaction strengths among the lowest-lying levels in the (A) over tilde state will aid the interpretation of the spectroscopy and dynamics of many higher-lying band structures, which are perturbed by analogous interactions. Published by AIP Publishing.