LASER-INDUCED FLUORESCENCE SPECTROSCOPY OF JET-COOLED SIC2

We present a spectroscopic study of the approximately A 1B2 <-- approximately X 1A1 system of jet-cooled SiC2 that includes both laser-induced fluorescence (LIF) excitation and dispersed fluorescence (DF) spectra. Rotational analysis of several previously unobserved bands in the LIF spectrum enables us to reassign the vibronic structure in the approximately A 1B2 <-- approximately X 1A1 system and gives an accurate term energy for the low-frequency, antisymmetric mode in the ground state, G(0,0,1) = 196.37 (4) cm-1. Analysis of DF spectra from ten different approximately A-state levels yields vibrational term energies for 43 levels in the ground state, including (0,0,nu-3") levels as high as nu-3" = 16. The rapidly decreasing level spacings in the (0,0,nu-3") progression, coupled with a dramatic decrease in the small inertial moment, give insight into the extreme anharmonic potential surface of the ground state. These data also provide indirect evidence for the onset of large-amplitude pseudorotation that samples both cyclic and linear minima. In contrast, the approximately A state is quite harmonic at the cyclic minimum, indicative of a more substantial barrier between the two isomers.