Experimental and Theoretical Studies of the Radiative Lifetime and Predissociation Rates of theA²Δ State of PH⁺

Lifetimes of 28 different rotational levels of the PH + A 2 Δ state υ' = 0, 1) have been measured using the High Frequency Deflection technique. Rotational levels above the dissociation limit of the ground state showed influences of predissociations. CASSCF calculations of the electronic transition moment of the A 2 Δ – X 2 Π transition made possible the determination of the lifetimes toward predissociation. CASSCF + CI calculations of the A 2 Δ, X 2 Π, 2 Σ - , and 4 Π state potential energy curves were performed. These curves were combined with experimental Rydberg-Klein-Dunham potential energy curves in a scaling procedure in order to obtain accurate potential energy curves which were used in a model calculation of the predissociation rates. These model calculations showed that a second order interaction between the A 2 Δ state and the 2 Σ - state via an excited 2 Π state is the most plausible mechanism for the observed predissociation.