A measurement of the lambda-type doubling spectrum of the CH radical by microwave-optical double resonance: further characterization of the A2Δ state

Abstract

Several lines in the lambda-doubling spectrum of the CH radical in its ground ²Π state have been recorded by the technique of microwave-optical double resonance. Individual lines in the (0, 0) band of the A²Π–X²Π system at 431 nm were pumped with a dye laser and the absorption of microwave radiation was detected as an increase in the level of fluorescence. The microwave transition frequencies were measured to an accuracy of 0.1 MHz and the results were used to determine values for the lambda-doubling parameters in the molecular effective Hamiltonian. Several lines in the (0, 0) band of the A–X system were also recorded with sub-Doppler line widths using the saturation technique of intermodulated fluorescence. The proton hyperfine structure was easily resolved. The very small effects of lambda-doubling in the A²Δ state were also detected for the higher rotational levels by precise measurement of the laser induced fluorescence spectrum. The values obtained for the parameters that described these effects in the molecular Hamiltonian are discussed.