TIME RESOLVED LASER INDUCED GRATING SPECTROSCOPY OF JET-COOLED $NO_{2}$

$^{1}$ T.S. Rose, W.L. Wilson, G. Wackerle, and M.D. Fayer, J. Chem. Phys. 86, 5370 (1987). $^{2}$ E.F. McCormick, S.T. Pratt, P.M. Dehmer and J.L. Dehmer, Chem. Phys. Lett. 227, 656 (1994).Author Institution: Department of Chemistry, Marquette UniversityWe report studies of jet-cooled $NO_{2}$ using time resolved laser induced grating spectroscopy (LIGS). The decay of a grating formed by two ``pump'' pulses tuned to probe vibronic transitions near 487 nm is monitored by a third ``probe'' pulse which is scanned in time. The decay profiles are found to strongly depend on polarization configuration. For certain configurations, pronounced oscillations (``quantum beats'') are observed which arise from coherent exciation of different hyperfine levels. These oscillations, which have previously been observed using LIGS for other $systems,^{1,2}$ give detailed information on the hyperfine structure of $NO_{2}$. We will report on our initial attempts to describe this phenomenon within a theoretical framework