Competitive channels in the interaction of Xe(3PJ) with Cl2, Br2 and I2. Atom transfer, excitation transfer, energy disposal and product rotational alignment

Abstract

The collision of electronically excited rare-gas atoms, e.g. Xe[np⁵(n+ 1)s] with the molecular halogens leads both to atom transfer (generating vibrationally and electronically excited rare gas halides) and to excitation transfer (generating electronically excited molecular halogens in a range of ion-pair excimer states). Translational energy utilisation and rotational alignment in the products of the atom transfer channel have been probed using a superthermal pulsed molecular beam technique, while the vibrational energy disposal and branching ratios determined under thermal collision conditions have been reassessed through direct inversion of the resolved chemiluminescence emission spectra. The range of halogen excimer states populated through excitation transfer has been identified by appeal to the literature.

The results confirm a steady increase in the importance of the excitation transfer channel in the series Cl₂, Br₂, I₂, together with a decline in the fraction of the reactive channel vibrational exo-ergicity, and implicate the excited ionic potential V[Xe⁺⋯X^–₂(²Π_g)] in the excitation transfer channel. In contrast to an earlier analysis, the vibrational energy disposal in XeX(B) is found to be unimodal with a linear surprisal. The rotational alignment of the XeX(B) perpendicular to the collision vector k increases with increasing collision energy, but does not reach the limiting value 〈P₂(Ĵ′·k)〉=–½, implying considerable repulsion between the nascent products of atom transfer.