15min:

MIN ZHANG, JIANQIANG MA, Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104; HAI-LUNG DAI, Department of Chemistry, Temple University, Philadelphia, PA 19122.

The collision relaxation cross section of highly vibrationally excited SO₂ at energies around 45,000 cm^\-1, which is just below the dissociation limit, has been measured for several \testitsingle, highly vibrationally excited levels. The measurement was conducted on rotationally cooled SO₂ in supersonic jet condition using quantum beat spectroscopy. Quantum beat in laser induced fluorescence from the C state is due to vibronic coupling between zero-order rovibronic levels of C and X states and can be analyzed to give the decay rate constants of the high vibrational levels of the X state. It is found that the collision relaxation cross section of the single highly vibrationally excited level shows a strong correlation with the corresponding vibronic coupling matrix element, likely reflecting that the part of the vibrational character of the single high vibrational level that gives a larger coupling with the C state also provide a stronger transition dipole moment contribution to its collision relaxation.