Predissociation dynamics in the A 3Π state of PH: An experimental and ab initio investigation

Abstract

An investigation into the predissociation dynamics of the A ³Π state of the PH radical is presented. Previous work on the v′ = 0 level found predissociation arising from a spin–orbit induced mixing with a repulsive ⁵Σ⁻ state correlating to ground state atomic fragments. The v′ = 1 and 2 levels, investigated for the first time here, show a strong Ω, parity and J dependence to the fluorescence lifetime, with low JΩ = 0 e parity levels having greatly elongated lifetimes compared to all the others. We present both experimental measurements of the lifetimes from laser induced fluorescence, and theoretical Fermi golden rule calculations on purely ab initio and experimentally refined potential energy surfaces and spin–orbit coupling matrix elements. MOLPRO 2000.1 was used to calculate all of the adiabatic potentials correlating to the first three atomic asymptotes and the spin–orbit coupling matrix elements between the electronic states involved in the predissociation at the CASSCF and MRCI level. The agreement between the purely ab initio and experimentally observed lifetimes is remarkably good.