New Investigations of the A2Δ-X2Π Band System in the CH Radical and a New Reduction of the Vibration-Rotation Spectrum of CH from the ATMOS Spectra

Abstract

Seven bands of the A2Δ-X2Π system of the CH radical have been photographed in emission from a Geissler tube using conventional spectroscopic techniques. Under high resolution and using Th lines as standards, as well as an interferometric comparator equipped with a photoelectric scanning device, the 0-0, 1-1, 2-2, 0-1, and 1-2 bands have been rephotographed and the 3-3 and 2-3 bands, with a total number of 144 lines, have been recorded for the first time. In the previously reported (J. Mol. Spectrosc.134, 305, 1989; 147, 16, 1991) evaluation of the ATMOS spectrum of CH for determining the molecular parameters we found total interparameter correlations between some of them, due to the absence of high-J lines of the P and Q branches. With the help of the precise constants obtained from our 0-0 band measurements (12 branches with Jmax = 24.5, f = 181, σ = 0.0025 cm−1) of the A2Δ-X2Π transition, we have been able to remove the correlations and obtain more accurate molecular parameters for the X2Π ground state. These constants have subsequently been used to derive new exact molecular parameters for the A2Δ , ν = 1, 2, and 3 levels of CH. The Λ-doubling constants in the A2Δ state were obtained for the first time. The complex vibrational analysis has been carried out to determine the equilibrium molecular constants. Also, RKR potentials and r-centroids have been calculated for both the combining states, as well as Franck-Condon factors for the A-X system.