DYNAMICS AND SPECTROSCOPY OF HIGHER BENDING VIBRATIONAL LEVELS OF PH2((A)OVER-TILDE-(2)A1)

The zero-pressure lifetimes of the bending vibrational levels from v(2 )' = 5,6, and 7 of PH2(($) over tilde A (2)A(1)) have been measured an d are found to be 720, 35 ((P)Q(1)), 26 (P-P(1)), and 3 ns, respective ly. The self-quenching constants are (11.0 +/- 0.9) X 10(-10) cm(3) mo lecule(-1) s(-1) for v(2)' = 5 and (7.4 +/- 1.4) [(P)Q(1)] and (7.7 +/ - 1.4) [P-P(1)] X 10(-10) cm(3) molecule(-1) s(-1) for v(2)' = 6. Evid ence of predissociation of PH2(A (2)A(1)) is shown by the sudden drop of its lifetime at v(2)' = 6, which however should start at v I = 4. A model of indirect predissociation mechanism has been proposed. Compos ite emissions due to simultaneous excitation of v(2)' = 5 and v(2)' = 6 and resulting in biexponential fluorescence decay curves have been i dentified in the laser-induced fluorescence (LIF) excitation spectrum of v(2)' = 5 where the spectroscopic assignment concerning some rotati onal lines and reported in literature has also been found to likely be incorrect. Besides, the origin of some unassigned peaks recorded in t he same spectrum has been found, through fluorescence decay studies, t o itself be v(2)' = 5.