Rovibrational State Mixing in Isolated Ground Electronic State Polyatomic Molecules

119 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1988.Rovibrational state mixing in ground electronic state polyatomic molecules has been studied using infrared laser induced fluorescence and stimulated emission pumping (SEP) spectroscopy. Molecules are cooled and isolated in supersonic molecular beams. A relationship between state mixing, measured as our experimental dilution factor, and rovibrational bath state density has been investigated from a study of IR fluorescence in the C-H stretch fundamental region of a variety of organic molecules. A threshold density of about 70 rovibrational states per cm$\sp{-1}$ with the correct J and symmetry to couple has been found to ensure mixing regardless of molecular structure except for the case of acetylenic C-H stretches, which appear to be less effective in state mixing. Fluorescence from the C-H stretch fundamental region of acetaldehyde shows that the extent of state mixing scales linearly with J, and the measured relative energy apportioned among the vibrational modes in the molecule following excitation has been explained by applying a rovibrational state mixing model. SEP spectra of glyoxal are recorded in the regions of C = 0 stretch fundamental and its overtones by employing X($\sp1$A$\sb{\rm g}$) $\gets$ A($\sp1$A$\sb{\rm u}$) rovibronic transitions up to energies of 7000 cm$\sp{-1}$ above the ground vibrational state. At low energies, only isolated states are observed. However, at higher energies, clumps of eigenstates can be seen demonstrating extensive state mixing with the dense bath states in the region.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD