Recoil energy distributions for dissociation of the van der Waals molecule p-difluorobenzene–Ar with 450–3000 cm⁻¹ excess energy

Abstract

<jats:p>Velocity map imaging has been used to measure the distributions of translational energy released in the dissociation of p-difluorobenzene–Ar van der Waals complexes from the 51¯, 31¯, 52¯, 3151¯, 53¯, 32¯, and 3251¯ states. These states span 818–3317cm−1 of vibrational energy and correspond to a range of energies above dissociation of 451–2950cm−1. The translational energy release (recoil energy) distributions are remarkably similar, peaking at very low energy (10–20cm−1) and decaying in an exponential fashion to approach zero near 300cm−1. The average translational energy released is small, shows no dependence on the initial vibrational energy, and spans the range 58–72cm−1 for the vibrational levels probed. The average value for the seven levels studied is 63cm−1. The low fraction of transfer to translation is qualitatively in accord with Ewing’s momentum gap model [G. E. Ewing, Faraday Discuss. 73, 325 (1982)]. No evidence is found in the distributions for a high energy tail, although it is likely that the experiment is not sufficiently sensitive to detect a low fraction of transfer at high translational energies. The average translational energy released is lower than has been seen in comparable systems dissociating from triplet and cation states.</jats:p>