Strong asymmetry induced ΔK a=3 transitions in the CH2 b 1B1→a 1A1 spectrum: A study by Fourier transform emission spectroscopy

Dispersed fluorescence spectra of the CH2b̃ 1B1→ã 1A1′2116 band were recorded by Fourier transform emission spectroscopy for a series of rotational levels in the b̃1 B1 (0,160,0) state. Strong ΔKa=3 transitions were observed with their intensity increasing as J increases in the ã 1A1 (0,1,0) state. The observed intensities could be well reproduced by a calculation based on a rigid asymmetric rotor Hamiltonian, in which CH2 was assumed to be linear in the b̃ 1B1 state and bent in the ã1A1 state. The calculation shows that the intensity of the ΔKa=3 transitions arises from the asymmetry of the ã 1A1 state.