The 365 nm 4 10 band of formaldehyde- d2: Analysis of rotational structure and Coriolis perturbations

Abstract

The 365 nm 4 1 0 (υ′= 0 - υ 4″ = 1) band in the A 1 A 2 - X 1 A 1 absorption system of formaldehyde- d 2, D 2CO, has been studied under high resolution. Rotational analysis procedures, which include approximations allowing for strong Coriolis perturbations to the υ 4″ = 1 level, are described and compared with more rigorous approaches. Rotational constants for both ground and excited vibronic states are determined by least-squares analysis, and significantly revised ground state vibrational frequencies reported, as follows: ν 4″ = 936.5 ± 0.1 cm −1, ν 6″ = 989.3 ± 0.1 cm −1. The coupling parameter ξ 64 a (2̃ Aζ 64 a ), associated with the a-axis Coriolis interaction between υ 4″ = 1 and υ 6″ = 1 levels, is determined to be |ξ 64 a | = 4.98 ± 0.02 cm −1. Several resonant Coriolis perturbations, arising from accidental coincidences between certain ν 4 rovibrational levels and levels of ν 6 and ν 3, are discussed and characterized. A simple theory for the intensity distribution in a pair of Coriolis-coupled vibronic bands is used to relate minor intensity anomalies observed in the 4 1 0 band to the apparent absence of the adjacent 6 1 0 band.