Photodissociation processes of a water–oxygen complex cation studied by an ion imaging technique. Issue 29 (16th July 2020)

• Record Type: Journal Article
• Authors: Nakashima, Yuji; Ito, Yuri; Okutsu, Kenichi; Nakano, Motoyoshi; Misaizu, Fuminori
• Is Part Of: Physical chemistry chemical physics. Volume 22:Issue 29(2020)
• Page Start: 16926
• Page End: 16933
• Publication Date: 2020-07-16
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.3
• DOI: 10.1039/d0cp03132a
• Languages: English
• ISSNs: 1463-9076

Abstract

Abstract : Photodissociation dynamics of O2 + –H2 O in the visible and ultraviolet regions was studied by ion imaging experiments and theoretical calculations. Abstract : Photochemistry of molecular complex ions in the atmosphere affects the composition, density, and growth of chemical species. Photodissociation processes of a mass-selected O2 + (H2 O) complex ion in the visible and ultraviolet regions were studied by ion imaging experiments and theoretical calculations. At 473 nm excitation, O2 + was the predominant photofragment ion produced. In this O2 + channel, the kinetic energy release was comparable to that estimated using a statistical dissociation model, and the anisotropy parameter was determined to be β = 1.0 ± 0.1. On the other hand, the H2 O + photofragment ion was mainly produced at 355 nm excitation. The kinetic energy release for the H2 O + channel was large and nonstatistical, and the anisotropy parameter was β = 1.9 ± 0.2. Theoretically, the 473 and 355 nm excitations were assigned to the B̃ 2 A′′ ← X̃ 2 A′′ and D̃ 2 A′′ ← X̃ 2 A′′ transitions, respectively, both of which were characterized by positive charge transfer from O2 to H2 O subunits. To further investigate the dissociation mechanisms, potential energy curves (PECs) and surfaces (PESs) for the O2 + (H2 O) ion were calculated for the ground and excited states. As a result, the H2 O + channel at 355 nm excitation was explained by rapid dissociation on the repulsive PES of the D̃ state, while rapid electronic relaxation from the B̃ to X̃ state followed by dissociation in the ground state was inferred in the O2 + channel at 473 nm excitation.