15min:

DAVID B. MOSS, Division of Science and Mathematics, College of General Studies, Boston University, Boston, MA 02215; RICHARD DUAN, MATTHEW P. JACOBSON, JONATHAN P. O'BRIEN AND ROBERT W. FIELD, Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139 .

Stimulated emission pumping (SEP) spectroscopy has been used to investigate the rovibrational level structure of S₀ acetylene with 0.1\,cm^-1 resolution at a vibrational energy of approximately 4400\,cm^-1. Both the e and f parity levels of the expected zero-order bright state ₂ + 4₄ ( \ell = 0, 2 ) are observed to be doubled by a rotationally inhomogeneous perturbation. SEP spectra obtained using S₁ intermediate levels with K = 1 vs. K = 0 reveal complementary intensity patterns, indicating that the perturbation follows a selection rule for vibrational angular momentum of \ell = odd. The perturbation is assigned to a Coriolis interaction between ₂ + 4₄ and the pure bending dark state 7₄. Zero-order vibrational energies and B values, as well as the Coriolis coupling coefficient, are derived from a fit of greater than 60 rovibrational levels of both parities with J = 1 to 13. Parameters derived from the fit are compared with predictions based on previous infrared and dispersed fluorescence studies. Axis-switching effects are also found to contribute significantly to the observed intensities.