title: The ν6 fundamental frequency of the Ã state of formaldehyde and Coriolis perturbations in the 3ν4 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 ν4 and ν6 (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 Ã (1)A2 electronic state, the analogous Coriolis interaction does not occur, because the Ã state suffers from a pseudo-Jahn-Teller distortion, which causes a double-well potential energy structure in the q4 (') out-of-plane coordinate, and which dramatically reduces the effective ν4 (') frequency. The ν4 (') frequency is reduced by such a great extent in the Ã state that it is the 3ν4 (') overtone which is near degenerate with ν6 ('). In the current work, we report the precise ν6 (') fundamental frequency in the Ã state, and we determine the strength of the a-axis Coriolis interaction between 3ν4 (') and ν6 ('). We also provide a rotational analysis of the ν4 (')+ν6 (') combination band, which interacts with 3ν4 (') via an additional c-axis Coriolis perturbation, and which allows us to provide a complete deperturbed fit to the 3ν4 (') rotational structure. Knowledge of the Coriolis interaction strengths among the lowest-lying levels in the Ã state will aid the interpretation of the spectroscopy and dynamics of many higher-lying band structures, which are perturbed by analogous interactions.
authors.affiliation: Institute for Physical Chemistry, University of Göttingen, Tammannstraße 6, 37077 Göttingen, Germany.
authors.forename: G Barratt
authors.initials: GB
authors.lastname: Park
authors.affiliation: Institute for Physical Chemistry, University of Göttingen, Tammannstraße 6, 37077 Göttingen, Germany.
authors.forename: Bastian C
authors.initials: BC
authors.lastname: Krüger
authors.affiliation: Institute for Physical Chemistry, University of Göttingen, Tammannstraße 6, 37077 Göttingen, Germany.
authors.forename: Sven
authors.initials: S
authors.lastname: Meyer
authors.affiliation: Max Planck Institute for Biophysical Chemistry, Göttingen, Am Faßberg 11, 37077 Göttingen, Germany.
authors.forename: Dirk
authors.initials: D
authors.lastname: Schwarzer
authors.affiliation: Institute for Physical Chemistry, University of Göttingen, Tammannstraße 6, 37077 Göttingen, Germany.
authors.forename: Tim
authors.initials: T
authors.lastname: Schäfer