Abstract
Despite the apparent simplicity of photodissociation in diatomic molecules, some of
the essential physics of this process is not understood when there is fine structure in
the atomic photofragments. Previous theories cannot treat the branching ratios and
angular distributions of the individual fine structure sublevels. We have developed a
complete quantum mechanical theory of the effects of nonadiabatic couplings and of
electronic angular momentum on the fine structure branching ratios, angular distributions,
and polarization in diatomic photodissociation. When the photofragments separate
with large relative kinetic energy, simple limiting expressions can be obtained for
branching ratios and the symmetry parameters which characterize fragment angular
distributions and polarized fluorescence from excited fragments. Information about
the symmetry of the molecular states involved in the optical transition which dissociates
the molecule may be deduced from fine structure branching ratios and asymmetry
parameters in the high energy limit. At low relative kinetic energies where non-adiabatic
couplings are crucial, cross sections and asymmetry parameters exhibit interesting
behavior which intimately reflect the shape of the dissociative molecular surfaces. We
employ the example of sodium hydride photodissociation to produce