Vibrational level structure of highly excited SO2 in the electronic ground state as studied by stimulated emission pumping spectroscopy

The stimulated emission pumping (SEP) spectroscopy is applied to SO2 cooled rotationally in a supersonic free jet to investigate the vibrational and rotational level structure in the 17 300–17 900, 21 400–21 500, and 22 200–22 500 cm−1 regions of the electronic ground state. It is concluded that respective vibrational levels are found to couple with each other by the network of Fermi and Coriolis interactions on the basis of the following grounds: (1) there are a number of Fermi pairs of the vibrational levels, and (2) the number of vibrational levels identified as the final states of the SEP transitions increases for rotational levels with larger rotational quantum numbers J and Ka. The distribution of the nearest neighbor vibrational level spacing shows that the vibrational quantum dynamics in the observed regions is almost quasiperiodic and the onset of the quantum chaos is estimated to be above 17 900 cm−1.