The first excited Ca-C-C bending vibration levels in the (A)over-tilde(2)Pi and (X)over-tilde(2)Sigma(+) states of the CaCCH radical: The Renner-Teller effect and K-type resonance

The 5(0)(1) and 5(1)(1) bands of the CaCCH <(A)over tilde (2) Pi>-<(X)over tilde (2) Sigma(+)> 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 (2) Delta and (2) Sigma 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 nu(5) = 101.394(1) and 102.940(1) cm(-1) for the <(A)over tilde (2) Pi> and <(X)over tilde (2) Sigma(+)> electronic states, respectively. The Renner-Teller parameter has been determined as epsilon(5) omega(5) = 3.528(14) cm(-1). The nonadiabatic parameter for the nu(5) mode, g(K) = 0.6542(10) cm(-1), is in accord with the observation that the (2) Delta(5/2) vibronic component lies above the normally highest kappa(2) Sigma component. (C) 1996 Academic Press, Inc.