PH2 internal energy distribution produced by the 193 nm photodissociation of PH3

Abstract

Experimental results involving 193 nm PH3 photodissociation are reported. Detection of the PH2 fragment using laser induced fluorescence suggests that PH2 is formed with appreciable internal excitation, but no quantitative results concerning nascent PH2 could be obtained using this direct method. In related kinetics studies, the reaction of thermalized (300 K) PH2 with O2 yields a rate coefficient of 2.7×10−13 cm3 molecule−1 s−1, while PH2+NO is rather unreactive (k<10−14 cm3 molecule−1 s−1). In separate experiments, sub-Doppler spectroscopy on the H-atom fragment at Lyman-α (121.6 nm) allowed the center-of-mass kinetic energy distribution to be extracted; the PH2 internal energy distribution was obtained using energy conservation. Most of the available energy (E° ≂hν−D0=22 000 cm−1) appears as PH2 internal excitation; the mean internal energy is 14 000 cm−1 and the distribution peaks at ∼19 000 cm−1. The experimental distribution compares favorably with a simple statistical (prior) calculation, and the agreement is discussed in terms of possible photodissociation mechanisms.