Observation of Non-Fluorescent Molecules by Laser-Induced Grating $Spectroscopy^{\\ast}$

Two-color laser-induced grating spectroscopy (LIGS) is a four-wave mixing technique that has been shown to be a potentially powerful tool for molecular $spectroscopy^{1}$ and photodissociation $dynamics.^{2}$ A distinct advantage of LIGS is that signal generation requires only molecular absorbance. While LIF is a tremendous weapon in the arsenal of the molecular spectroscopist, it is limited to molecules that fluoresce with reasonable quantum yield. Many important combustion radicals and large aromatic molecules do not fluoresce. We present the results of a model study aimed at exploring the use of LIGS to observe non-fluorescent molecules. We demonstrate that molecules that predissociate or experience other rapid nonradiative decay can, in many instances, be probed using this technique.