Sub-Doppler nonlinear spectroscopy as a probe of photodissociation dynamics

Abstract

The nonlinear optical technique of degenerate four-wave mixing (DFWM) is shown to be an effective tool for the interrogation of nascent product molecules generated during a photodissociation event. By combining an absorption-based, beam-like response with the sensitivity afforded by full resonant enhancement, this scheme provides an attractive alterative to the ubiquitous laser-induced fluorescence (LIF) methodology. DFWM spectroscopy has been used to probe the unrelaxed hydroxyl (OH) radicals formed upon 266 nm photolysis of hydrogen peroxide (HOOH), with a sub-Doppler experimental configuration enabling extraction of both scalar and vector properties. In particular, the rovibrational population distribution of the ground electronic state fragments, as well as the spatial alignment of their rotational angular momenta, have been measured. These results are compared with those obtained in previous LIF studies, thereby demonstrating the utility of four-wave mixing techniques for the quantum state-specific characterization of nascent reaction products.