The far-infrared and microwave spectra of the CH radical in the v =1 level of the X 2Π state

Abstract: Transitions between the spin–rotational levels of the 12CH radical in the v =1 level of the X 2Π state have been studied by the technique of laser magnetic resonance at far-infrared wavelengths. The data have been combined with a measurement of lambda-doubling transition frequencies at 7GHz to determine an improved set of molecular parameters for CH in the v =1 level. The parameters provide information on the effects of vibrational excitation on the structural properties of CH. Accurate predictions of the transition frequencies between the low-lying levels of the radical in the absence of a magnetic field have also been made. Small inconsistencies in the least-squares fit of the laser magnetic resonance data prompted re-measurement of three far-infrared laser frequencies, the 122.5μm line of CH2F2 pumped by 9R(22), the 122.5μm line of CH2F2 pumped by 9P(8) and the 554.4μm line of CH2CF2 pumped by 10P(14). The new measurements differ by as much as 3.8MHz from those made previously and are more accurate; they also remove the inconsistencies in the fit. The re-measured frequencies of the two 122.5μm lines are identical within experimental error which suggests that the far-infrared lasing transition is the same, namely the rR23(32) transition in the v 9=1 level of CH2F2. [Copyright &y& Elsevier]