Vector Correlations and Their Applications in Photodissociation Dynamics Study

The velocity map ion imaging technique is a powerful tool for studying photodissociation. Determination of correlated product internal and translational energy distribution, as well as vector correlations, can elucidate fundamental dynamics of the photo-induced reactions. Vector correlations, which describe the relative orientations of the transition dipole moment of the parent molecule μ, recoil velocity vector v, and angular momentum vector of photofragment rotation j are sensitive probes of the stereodynamics of photodissociation reactions. The focus of this dissertation is the development and application of a method for extracting vector correlation, from experimental angular distribution of sliced or reconstructed non-sliced images generated by 2+1 REMPI. Two general approaches for applying the new equations; direct inversion and forward convolution, are presented. The new method is tested with images of OCS photodissociation at 230 nm and NOv2 photodissociation at 355 nm and the results are compared to previous publications. The ultraviolet photodissociation of carbonyl sulfide (OCS) is an important system, not only because of its role in atmospheric chemistry, but also because of its significance as a benchmark system of photodissociation via multi-excited states. We are particularly interested in the wavelength dependence of the dynamics. The OCS photodissociation dynamics of the dominant S(^1Dv2) channel near 214 nm have been studied, as an application of our new method mentioned above. We report a vibrational branching ratio of 0.79/0.21 for CO v=0/v=1, indicating substantially higher vibrational excitation than that observed at longer wavelengths. The CO rotational distribution is bimodal for both v=0 and v=1, although the bimodality is less pronounced than at longer wavelengths. The measurements of vector correlations indicate that excitations to both the 2^1A′ (A) and 1^1A″ (B) states are important in the lower-j part of the rotational distribution, while only 21A′ state contributes to the upper part. The discovery is consistent with the previous work at longer wavelengths. The computational chemistry results from Dr. George McBane support the experimental results, and also suggest that the highest-j peak arises from molecules that begin on the 2^1A’ state but make non-adiabatic transitions to the 1^1A’ (X) state during the dissociation