On the Wavelength-Dependent Photochemistry of the Atmospheric Molecule CF3COCl

Jiří Janoš; Ivo S Vinklárek; Jozef Rakovský; Deb Pratim Mukhopadhyay; Basile F E Curchod; Michal Fárník; Petr Slavíček

doi:10.1021/acsearthspacechem.3c00196

On the Wavelength-Dependent Photochemistry of the Atmospheric Molecule CF₃COCl

ACS Earth Space Chem. 2023 Oct 16;7(11):2275-2286. doi: 10.1021/acsearthspacechem.3c00196. eCollection 2023 Nov 16.

Authors

Jiří Janoš¹, Ivo S Vinklárek², Jozef Rakovský², Deb Pratim Mukhopadhyay², Basile F E Curchod³, Michal Fárník², Petr Slavíček¹

Affiliations

¹ Department of Physical Chemistry, University of Chemistry and Technology, Technická 5, Prague 6 166 28, Czech Republic.
² Department of Dynamics of Molecules and Clusters, J. Heyrovský Institute of Physical Chemistry, v.v.i., The Czech Academy of Sciences, Dolejškova 2155/3, 182 23 Prague, Czech Republic.
³ Centre for Computational Chemistry, School of Chemistry, University of Bristol, Bristol BS8 1TS, U.K.

Abstract

The wavelength control of photochemistry usually results from ultrafast dynamics following the excitation of different electronic states. Here, we investigate the CF₃COCl molecule, exhibiting wavelength-dependent photochemistry both via (i) depositing increasing internal energy into a single state and (ii) populating different electronic states. We reveal the mechanism behind the photon-energy dependence by combining nonadiabatic ab initio molecular dynamics techniques with the velocity map imaging experiment. We describe a consecutive mechanism of photodissociation where an immediate release of Cl taking place in an excited electronic state is followed by a slower ground-state dissociation of the CO fragment. The CO release is subject to an activation barrier and is controlled by excess internal energy via the excitation wavelength. Therefore, a selective release of CO along with Cl can be achieved. The mechanism is fully supported by both the measured kinetic energy distributions and anisotropies of the angular distributions. Interestingly, the kinetic energy of the released Cl atom is sensitively modified by accounting for spin-orbit coupling. Given the atmospheric importance of CF₃COCl, we discuss the consequences of our findings for atmospheric photochemistry.