An experimental investigation of predissociation effects in theA3Π-X3Σ-transition of PH

The high frequency deflection technique has been applied to the PH A 3Π-X 3Σ- transition for measurements of the fluorescence lifetimes of individual rotational levels of the v′ = 0 vibrational level of the A 3Π state. The onset of a rotationally dependent predissociation is observed at about J′ = 11 as a decrease in the measured lifetimes. The predissociation is interpreted in terms of a first-order spin-orbit interaction between the A 3Π state and a repulsive 5Σ- state arising from the ground state dissociation products. The average radiative lifetime of low rotational levels is 450 ns and the observed predissociation gives an upper limit of 3·74ev to the PH dissociation energy.