Imaging the elusive C–C bond dissociation channel of photoexcited ethyl radical

Abstract

The C–C bond dissociation channel of the ethyl (CH${}_3$–CH${}_2$) radical is investigated at 197.4, 199.98 and 201 nm by velocity map imaging and resonance enhanced multiphoton ionisation (REMPI) detection of the produced CH${}_3$ fragments. On the light of high-level ab initio calculations performed in this work, up to four dissociation pathways are identified leading, respectively, to ground state CH${}_3$ radicals in correlation with CH${}_2$ fragments in the first four electronic states. The major pathway is associated with threshold dissociation over an exit barrier located at the point of a conical intersection between the initially populated 3$p_{A^{\prime }}$ state and a dissociative valence state. As discussed in the text, the concomitance of both features opens the narrow window in which C–C bond dissociation occurs for ethyl and, presumably, for other similar alkyl radicals.

GRAPHICAL ABSTRACT

Acknowledgments

This research has been carried out within the Unidad Asociada Química Física Molecular between the Departamento de Química Física of Universidad Complutense de Madrid (UCM) and the Consejo Superior de Investigaciones Científicas (CSIC). The Center for Ultrafast Lasers of UCM, the Centro de Supercomputación de Galicia (CESGA, Spain) and the Centro Técnico de Informática (CTI, CSIC) are acknowledged for the use of their resources.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

D. V. C. acknowledges financial support from Spanish MINECO under the FPI predoctoral program. A. G.-V., O. Y., and A. B. acknowledge funding from the I-COOP program from Consejo Superior de Investigaciones Científicas (CSIC) [I-COOP COOPB20364], which made possible a research stay of A.B. at Instituto de Física Fundamental, CSIC. This work has been financed by the Spanish Ministry of Science and Innovation [PGC2018-096444-B-I00].