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oai:docta.ucm.es:20.500.14352/1240562026-05-21T11:18:08Zcom_20.500.14352_14col_20.500.14352_15

00925njm 22002777a 4500 dc Murillo Sánchez, Marta Luisa author Marggi Poullaín, Sonia author Limao-Vieira, Paulo author Zanchet, Alexandre author De Oliveira, Nelson author González Vázquez, Jesús author Bañares Morcillo, Luis author 2025-01-18 The photodissociation dynamics of vinyl iodide upon photoexcitation at 199.2 and 200 nm are investigated in a joint theoretical and experimental study. The gas-phase absorption spectrum measured by Fourier transform spectroscopy along with the use of synchrotron radiation is reported and a reassignment of the excited electronic states responsible for the absorption at the energy range of interest is proposed. Femtosecond time-resolved velocity map imaging in conjunction with resonance enhanced multiphoton ionization detection of the I(2P3/2) and I*(2P1/2) photofragments have been carried out. The experimental results are discussed in view of high-level ab initio calculations including potential energy curves and semiclassical dynamics. Three conical intersections (CIs) governing the dynamics are identified in a search for stationary points using spin–orbit gradients. Based on these results, a complete picture of the photodissociation dynamics of vinyl iodide is obtained. Photoexcitation at 200 nm, associated with a nI(⊥)σ* transition, leads to a fast dissociation occurring in a repulsive potential energy surface, which is mediated by a CI with a low-lying excited electronic state. This mechanism resembles the typical dissociation of alkyl iodides in the first absorption A-band. In contrast, one-photon excitation at 199.2 nm into a well-defined vibronic structure of the absorption spectrum is assigned to a nI(‖)π* transition. The subsequent dissociation dynamics from that state features an ultrafast electronic predissociation with sub-200 femtosecond reaction time. State-switching at a first CI with a low-lying electronic state governing the mechanism involves states of completely different character, occurring in less than 20 fs. This remarkably fast process takes place through an initial stretch of the C[double bond, length as m-dash]C bond, followed by a C–I elongation with subsequent vibrational activity in the C[double bond, length as m-dash]C stretch mode. Murillo-Sánchez, Marta L., et al. «Non-Adiabatic Photodissociation Dynamics of Vinyl Iodide from Nσ* and Nπ* Transitions». Physical Chemistry Chemical Physics, vol. 27, n.o 16, 2025, pp. 8354-67. 10.1039/D5CP00236B https://hdl.handle.net/20.500.14352/124056 https://doi.org/10.1039/D5CP00236B Non-adiabatic photodissociation dynamics of vinyl iodide from nσ* and nπ* transitions