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 ν 4 and ν 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 singletà 1 A 2 electronic state, the analogous Coriolis interaction does not occur, because theà 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 ν 4 frequency. The ν 4 frequency is reduced by so great an extent in theà state that it is the 3ν 4 overtone which is near degenerate with ν 6. In the current work, we report the precise ν 6 fundamental frequency in theà state, and we determine the strength of the a-axis Coriolis interaction between 3ν 4 and ν 6. We also provide a rotational analysis of the ν 4 + ν 6 combination band, which interacts with 3ν 4 via an additional c-axis Coriolis perturbation, and which allows us to provide a complete deperturbed fit to the 3ν 4 rotational structure. Knowledge of the Coriolis interaction strengths among the lowest-lying levels in theà state will aid the interpretation of the spectroscopy and dynamics of many higher-lying band structures, which are perturbed by analogous interactions.
Quantum state resolved molecular beam scattering studies of small polyatomic molecules from metal surfaces present new challenges for experimentalists, but provide unprecedented new opportunities for detailed study of polyatomic molecular dynamics at surfaces. In the current work, we report preliminary characterization of the scattering of formaldehyde from the Au(111) surface. We report the measured desorption energy (0.31 eV), and characterize the distinct trapping-desorption and direct scattering channels, via the dependence of the scattered velocity and rotational distributions on surface temperature and incident molecular beam energy. Finally, we estimate the trapping probability as a function of incidence energy, which indicates the importance of molecular degrees of freedom in the mechanism for trapping.
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