title: The First Excited Ca-C-C Bending Vibration Levels in the A2Pi and X2Sigma+ States of the CaCCH Radical: The Renner-Teller Effect and K-type Resonance
abstract: The 5(1)0 and 5(1)1 bands of the CaCCH A2Pi-X2Sigma+ transition, corresponding to the Ca-C-C bending mode, have been rotationally analyzed through cw dye laser excitation and dispersed fluorescence with a CCD array detector. The upper state is subject to Renner-Teller and spin-orbit couplings, and strong K-type resonance interactions were observed between the nearby 2Delta and 2Sigma vibronic components. A model that invokes a full matrix treatment of these interactions was employed in a least-squares fit of a total of 708 rotational lines of the two bands, recorded with high precision. The fundamental bending frequencies have been determined as nu5 = 101.394(1) and 102.940(1) cm-1 for the A2Pi and X2Sigma+ electronic states, respectively. The Renner-Teller parameter has been determined as epsilon5omega5 = 3.528(14) cm-1. The nonadiabatic parameter for the nu5 mode, gK = 0.6542(10) cm-1, is in accord with the observation that the 2Delta5/2 vibronic component lies above the normally highest kappa2Sigma component.
authors.affiliation: Department of Chemistry, Dalhousie University, Halifax, B3H 4J3, Canada
authors.initials: M
authors.lastname: Li
authors.initials: JA
authors.lastname: Coxon