Dispersed fluorescence spectroscopy of excited rovibrational states in S formaldehyde

Abstract

Dispersed fluorescence (DF) spectroscopy is used to explore the rovibrational structure of highly excited S₀ formaldehyde (H₂CO). A narrowband laser excites formaldehyde molecules to a single S₁ rovibronic quantum state, and the resulting fluorescence is dispersed with a monochromator. DF spectra of ten vibrational levels with excitation in ν₂, the carbon–oxygen stretch, and ν₄, the out‐of‐plane bend, have been recorded, and the effective A, B, and C rotational constants are extracted. Five of the effective A rotational constants and seven of the effective B and C rotational constants are new to the literature. The dependence of these effective rotational constants on vibrational state are both calculated and discussed with regard to both the present and previous experiments. Particular attention is given to the manner in which that the effective A rotational constant depends on increasing excitation in ν₄ due to the strong A‐axis ν₄/ν₆ Coriolis interaction. For states where v₂ is less than two, quantitatively accurate values for the nonlinear dependence of the A rotational constant on quanta in ν₂ and ν₄ is achieved by a simultaneous consideration of the strong A‐axis ν₄/ν₆ Coriolis interaction and the 1₁↔4₂, 1₁↔6₂, and 5₁↔2₁6₁ Fermi interactions.