Dynamics of Molecular Photofragmentation

Abstract

AbstractPhotodissociation dynamics provides a vast amount of information in understanding chemical dynamics. The obtained energy‐release data describe scalar properties of the chemical interaction which can be compared directly with the results of classical or quantum mechanical scattering calculations. However, even a complete knowledge of the product distribution provides only a limited view of the dissociation process, as long as vector correlations between observables are not taken into account. These correlations can be obtained by measuring Doppler profiles of the products using polarized light and different excitation and detection geometries. – The correlation between the transition dipole moment μ in the parent and the recoil velocity v of the fragment, as well as the correlation between μ and the rotational vector J of the product, may reveal the symmetry and geometry of the dissociative state. Any decrease in fragment anisotropy of directional properties caused by parent rotation gives information on the lifetime of the parent excited state. Very recently a substantial progress in the field of photodissociation dynamics has been achieved by observing not only the <μJ> and <μv> correlation but also the correlation between the rotational and translation motion of the fragment, <μJ>, and between μ, v, and J. – Observation of fragment anisotropy can also be used to discriminate between two different dissociation channels. If two electronic states are responsible for the dissociation process, the observed line shape is a linear combination of two Doppler profiles. The bipolar moments of the <μv> correlation for each contributing parent dissociation channel can be used to calculate the product state distribution referring to the two different fragmentation channels. As an example, the dynamics of the photofragmentation of the H2O2 and D2O2 is analyzed by a characterization of scalar and directed properties of the recoiling OH fragments.