Near ultraviolet photolysis of phosphine studied by H atom photofragment translational spectroscopy

Abstract

We report time-of-flight measurements of the H atom fragments arising in the photodissociation of phosphine at three near ultraviolet excitation wavelengths—218.2 nm, 221.6 nm, and 228.0 nm. For these wavelengths, energetic considerations dictate that ground state [Formula: see text] fragments must be the partner product of the primary photolysis event. The measured H atom kinetic energy distributions indicate that internal excitation of these partner fragments accounts for the major part [Formula: see text] of the available energy, in excess of that required to break the H—PH2 bond, provided by the photon. Inspection of the poorly resolved structure evident near the peak of the H atom kinetic energy distribution suggests the presence of substantial bending excitation and a-axis rotational excitation in the PH2 partner fragment. The H atom kinetic energy distribution also shows clear evidence of atoms arising from secondary photolysis of the primary [Formula: see text] fragments. This secondary photo-dissociation is observed to show a marked anisotropy, consistent with a perpendicular photo-excitation of the [Formula: see text] fragment. Arguments are presented which indicate that the secondary photolysis leads both to the formation of PH(X) fragments, carrying high levels of rotational excitation, and to the three-body atomisation process.