Two separate studies of the CD radical in vibrationally excited levels of its X2Π ground state have been made by the technique of laser magnetic resonance. The first of these studies was in the far-infrared; rotational transitions of CD in the v=1 and 2 levels have been detected. The second study was carried out in the mid-infrared using a carbon monoxide laser magnetic resonance spectrometer. In these experiments, transitions in the (1,0), (2,1), and (3,2) bands have been detected. All the available data on CD in its X2Π state have been used to determine an improved set of molecular parameters for the CD radical. In addition to the above data sets, previous far-infrared laser magnetic resonance on the CD radical in the v=0 level and FTIR observations of the (1,0) and (2,1) bands have been included. The principal molecular parameters determined are: ν0=2032.03360(18)cm-1, ωexe=34.72785(58)cm-1, B0=7.7018632(14)cm-1, αB=-αe=-0.212239(11)cm-1, where the figures given in parentheses are one standard deviation from the least squares fit. A small but significant dependence of the orbital contribution to the magnetic dipole moment on the vibrational quantum number is detected. This may reflect the mixing between the X2Π and a4Σ- states of CD.

Re-vibrational transitions in the (1-0) band of the electronic ground state X (3) Pi of the SiC radical have been observed with high accuracy using CO2-Faraday laser magnetic resonance (LMR) spectroscopy. The molecule parameters of this electronic state were determined in a nonlinear least-squares fit including all relevant experimental data of earlier work. No indication for a perturbation by other electronic states could be found. For the band origin of the fundamental band we obtained 953.32062(27) cm(-1). (C) 1997 Elsevier Science B.V.

The gas phase spectrum of the C2H radical in the region between 3191 and 3342 cm−1has been studied using a Faraday LMR spectrometer with a CO overtone laser. The C2H molecules were produced in an electric dc glow discharge of normal type containing a mixture of helium, acetylene, and hydrogen. We observed two bands of theX2Σ+→A2Π electronic transition with origins at 3321 and 3229 cm−1. The lower level of both bands was the first excited bending level of the electronic ground stateX. The upper levels were assigned to two2Π vibronic levels with term values of 3693 and 3600 cm−1, respectively. They correspond to mixtures of vibrationally excited levels of theXelectronic state with the lowest vibronic level of the first excited electronic stateA. From the analysis of the spectra we could determine the orbitalgfactors of the upper levels. These parameters are a very sensitive measure for the mixing between theXandAelectronic states. The experimentally derived values were compared with theoretical values, obtained byab initiocalculations, and could be explained by the theoretical model using an improved energy distance between theXandAstates.