Photodissociation of the alkali iodides at 347.1 nm: Experimental angular distributions and dynamic model for their interpretation

Abstract

The angular distributions of the alkali photofragment resulting from photodissociation of a molecular beam of NaI, KI, CsI, or RbI by a pulsed, linearly polarized laser beam at 347.1 nm have been measured. At the wavelength used, only production of ground state atoms is energetically feasible. The angular distributions indicate a trend in the perpendicular:parallel transition ratio from about 4:1 for NaI to about 2:1 for RbI and CsI. This interpretation assumes Hund’s case (c) coupling and excited states of pure perpendicular or parallel symmetry. A new model was developed to calculate the laboratory distribution from any center of mass distribution, including those resulting from multiphoton or saturated transitions. The individual counting model (ICM) simultaneously takes into account contributions from excited state lifetime, rotational distribution, and translational motion of the molecule. It is concluded that further study of the systems at several wavelengths in the lowest energy absorption band is necessary to unambiguously characterize the symmetry and electronic coupling of the low-lying excited states of the alkali iodides.