THE 248 NM PHOTOLYSIS OF PHOSPHORUS TRICHLORIDE AND PHOSPHORUS TRIBROMIDE

The 248 nm excimer laser photolysis Of PCl3 and PBr3 has been studied. Emission in the region 200-600 nm is found to result from two- or thr ee-photon processes involving short-lived (less-than-or-equal-to 20 ns ) excited species. In the case of PBr3, emission is observed from the D, D' and E states of Br2 formed either by direct multiphoton dissocia tion of PBr3 or by 248 nm excitation of Br2 formed by single-photon di ssociation of PBr3. The corresponding processes are energetically inac cessible for PCl3 and no emission from molecular chlorine is observed. There are additional emission features in both photolysis systems tha t do not correspond to any reported states of X2, PX or PX2 (X = Cl or Br) and it is suggested that these features might be from previously unreported states of the phosphorus dihalides (PCl2 and PBr2). For bot h PCl3 and PBr3, we observe an excitation that is resonant with the 24 8 nm laser line which shows a progression with a spacing of 387 +/- 5 and 140 +/- 10 cm-1, respectively. This is attributed to 248 nm excita tion of a vibrationally excited species created in a ground or low-lyi ng electronic state by 248 nm photolysis. For PBr3, we suggest that th e pumped state could either be the A' state of Br2 or else the ground state of PBr2 where the observed separation would correspond to the be nding frequency, nu2. For PCl3, we can discount excitation of PCl2 and there is no previously reported state of PCI or Cl2 that can be invol ved.