Ultraviolet photodissociation dynamics of PCl3 at 235 nm: three-dimensional ion imaging and theoretical analysis

Abstract

The photodissociation dynamics of PCl₃ at 235 nm has been studied by monitoring ground state Cl(²P_3/2) and spin–orbitally excited Cl(²P_1/2) atoms by resonance enhanced multiphoton ionization (REMPI). Also, the PCl_n⁺ (n = 0, 1, 2) photoions were observed non-resonantly. The speed distributions and speed-dependent anisotropy parameters β for all these particles have been determined by three-dimensional photofragment ion imaging. The β parameters are close to zero for all these particles. The relative yield of excited Cl(²P_1/2) atoms for photodissociation of PCl₃ is 0.49 ± 0.03. The speed distributions of Cl(²P_3/2) and Cl(²P_1/2) atoms are bimodal, mainly resulting from the sequential photodissociation PCl₃ → PCl₂ → PCl. Near-resonant two-photon ionisation followed by near-resonance one-photon photodissociation is proposed for the production of PCl_n⁺ photoions. Using Condon's reflection principle, we constructed the vibrational mode dependent absorption spectrum by accounting for the vibrational motion for all six normal coordinates. As a result, the absorption of 235 nm radiation by PCl₃ occurs due to zero vibrational motion rather far from the equilibrium geometry. In particular, movement along the Q₂ normal coordinate results in an efficient photoinduced transition into the excited state à of D_3h symmetry due to a parallel transition.