BENDING OVERTONES AND BARRIER HEIGHT OF A-1A1 CH2 BY FLASH-PHOTOLYSIS STIMULATED-EMISSION PUMPING

The J≤7 and Ka ≤3 rotational levels of the bending vibrational overtones, (0,2,0), (0,3,0), and (0,4,0), and the ( 1,1,0) combination band of ã1A1CH2 were characterized in detail by stimulated emission spectroscopy. The methylene was generated from ketene photolysis. Spectroscopic analyses using a rigid rotor Hamiltonian gave the vibrational term values and rotational constants. The latter were found to be strongly J and Ka dependent suggesting the inadequacy of the rigid rotor Hamiltonian for calculating the rotational energy to high accuracy. Effects of Coriolis, Fermi, and singlet-triplet perturbations were all observed in the spectra and discussed. Abnormally intense ΔK a= 3 transitions were observed in the ã←b̃, 2 216 and 2316 bands. From fitting the experimentally measured bending vibrational term values by a model calculation based on the WKB theory, the barrier height to linearity in the ã state was determined to be 9870 cm -1 © 1990 American Institute of Physics.