Photodynamics of charge transfer and ion-pair states of Cl2:Xe complexes in liquid Ar

Abstract

Sequential two photon studies of Xe:Cl 2 complexes in liquid Ar are reported. The first photon prepares the excited state complex Xe:Cl 2 ͑ 3 ⌸ u ͒, which radiatively relaxes with a lifetime of 10Ϯ1 s ͑22Ϯ2 s for the uncomplexed Cl 2 ͑ 3 ⌸ u ͒͒. A second photon accesses either the molecular ion pair state, Xe:Cl ϩ Cl Ϫ , or the contact charge transfer transition, Xe ϩ Cl 2 Ϫ. The latter dissociates to Xe ϩ Cl Ϫ ϩCl even though the product is formed at threshold. The former undergoes charge rearrangement and decays radiatively via Xe ϩ Cl 2 Ϫ ͑ 2 ⌺ u ͒→XeCl 2 ͑ 1 ⌺ g ͒. Analysis of the excitation and emission spectra of the key intermediate in laser induced harpoon reactions, Xe ϩ Cl 2 Ϫ , leads to the conclusions that the complex is linear in both ionic and neutral states, and allows a direct contrast between dissociation dynamics on ionic versus neutral surfaces.

Molecular Photodynamics in Rare Gas Solids

“…Photoinduced harpoon reactions, in which guest−host intermolecular charge-transfer states are accessed optically, are designed to probe reactive dynamics over ionic surfaces and serve as model systems to advance theoretical rigor. The classic case of Cl 2 /Xe, which has been extensively studied in the gas phase, − in small − and large , van der Waals clusters, in the supercritical fluid, in the liquid phase, − in matrixes, ,,,, and in solids under pressure, , serves as a useful example to highlight the distinctive features of dynamics on ionic surfaces.…”

“…The intermolecular charge-transfer transition of the Xe ... Cl 2 contact pair can be directly accessed optically. , In condensed media, dielectric solvation of the ionic terminal state shifts this transition to the near-UV, and a relatively simple model can reproduce the absorption bands, as shown for all the molecular halogens in liquid Xe 65 as well as in solids of Xe and Kr . Upon excitation, the vertically created Xe + Cl 2 - ion-pair state, which was recently isolated in liquid Ar, evolves along the attractive Xe + ···Cl - coordinate and the repulsive Cl - ···Cl coordinate, toward the Xe + Cl - + Cl product of the harpoon reaction. This evolution is probed in real time in liquid Xe, where it has been shown that the reaction can be arrested by stimulating the transition from the ionic to the neutral surface .…”

Energy disposal in the two-photon laser-assisted reaction in xenon and chlorine gas mixtures

“…35 Similar arguments, however, can be presented, mutatis mutandis, for the dynamics on a reactive PES appropriate for a linear geometry.…”