Imaging transient molecular configurations in UV-excited diiodomethane

Abstract

Femtosecond structural dynamics of diiodomethane ($\mathrm{C}{\mathrm{H}}_2{\mathrm{I}}_2$) triggered by ultraviolet (UV) photoabsorption at 290 nm and 330 nm are studied using time-resolved coincident Coulomb explosion imaging driven by a near-infrared probe pulse. We map the dominant single-photon process, the cleavage of the carbon-iodine bond producing rotationally excited $\mathrm{C}{\mathrm{H}}_2\mathrm{I}$ radical, identify the contributions of the three-body ($\mathrm{C}{\mathrm{H}}_2+\mathrm{I}+\mathrm{I}$) dissociation and molecular iodine formation channels, which are primarily driven by the absorption of more than one UV photon, and demonstrate the existence of a weak reaction pathway involving the formation of short-lived transient species resembling iso-$\mathrm{C}{\mathrm{H}}_2\mathrm{I}-\mathrm{I}$ geometries with a slightly shorter I-I separation compared to the ground-state $\mathrm{C}{\mathrm{H}}_2{\mathrm{I}}_2$. These transient molecular configurations, which can be separated from the other channels by applying a set of conditions on the correlated momenta of three ionic fragments, are formed within approximately 100 fs after the initial photoexcitation and decay within the next 100 fs.

arXiv comment9 pages, 10 figures

References in corpus (3)

• Probing the UV-Induced Photodissociation of CH${}_{\text{3}}$I and C${}_{\text{6}}$H${}_{\text{3}}$F${}_{\text{2}}$I with Femtosecond Time-Resolved Coulomb Explosion Imaging at FLASH
• Differentiating Three-Dimensional Molecular Structures using Laser-induced Coulomb Explosion Imaging
• A Coincidence Velocity Map Imaging Spectrometer for Ions and High-Energy Electrons to Study Inner-Shell Photoionization of Gas-Phase Molecules

Cited by in corpus (1)

• Ground and low-lying excited state potential energy surfaces of diiodomethane in four dimensions