A velocity map imaging study of the photodissociation of the methyl iodide cation

• Published in: Physical chemistry chemical physics : PCCP 2017-03, Vol.19 (11), p.7886-7896
• Main Authors: Marggi Poullain, S, Chicharro, D. V, González-Vázquez, J, Rubio-Lago, L, Bañares, L
• Format: Article
• Language: English
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c7cp00319f

The photodissociation dynamics of the methyl iodide cation has been studied using the velocity map imaging technique. A first laser pulse is used to ionize methyl iodide via a (2 + 1) REMPI scheme through the 5pπ → 6p Rydberg state two-photon transition. The produced CH 3 I + ( X&cmb.tilde; 2 E 3/2 ) ions are subsequently excited at several wavelengths between 242 and 260 nm. The reported translational energy distributions for the methyl and iodine ions present a Boltzmann-type unstructured distribution at low excitation energies as well as a recoiled narrow structure at higher excitation energies highlighting two different dissociation processes. High level ab initio calculations have been performed in order to obtain a deeper understanding of the photodissociation dynamics of the CH 3 I + ion. Direct dissociation on a repulsive state from the manifold of states representing the B&cmb.tilde; excited state leads to CH 3 + ( X&cmb.tilde; 1 A 1 ′) + I*( 2 P 1/2 ), while the CH 3 + I + ( 3 P 2 ) channel is populated through an avoided crossing outside the Franck-Condon region. In contrast, an indirect process involving the transfer of energy from highly excited electronic states to the ground state of the ion is responsible for the observed Boltzmann-type distributions. The photodissociation dynamics of the methyl iodide cation has been studied using velocity map imaging and ab initio theory to disentangle the dissociation mechanisms.