VIBRATION-ROTATION SPECTROSCOPY BY STIMULATED EMISSION PUMPING IN A SUPERSONIC BEAM: a-AXIS CORIOLIS COUPLED $\nu_{4}=1$ and $\nu_{8}=1$ LEVELS OF X1Ag GLYOXAL

Author Institution: Chemistry Department, University of Pennsylvania PhiladelphiaRotational cooling in a supersonic expansion combined with the rotational-level selection in stimulated emission pumping allowed vibrational levels of medium-size molecules to be studied with single rotational-level resolution and selectivity. We have shown that the vibration-rotation spectra of X3 Ag glyoxai can be obtained at sub-mTorr pressure and $0.04 cm^{-1}$ resolution. As a demonstration, the $\nu_{4}=1 C-C$ stretch and $\nu_{5}=1 CH$ wag levels were studied. The vibrational term values were determined as 1065.78 and $1048.08 cm^{-1}$, respectively. The greatly reduced rotational congestion in the spectra makes the assignment straightforward. In addition to the determination of their rotational constants, it was found that the two vibrational levels are strongly coupled to each other through an a-axis Coriolis coupling