Substituent effects on H3+ formation via H2 roaming mechanisms from organic molecules under strong-field photodissociation.

Roaming chemical reactions are often associated with neutral molecules. The recent findings of roaming processes in ionic species, in particular, ones that lead to the formation of H3+ under strong-field laser excitation, are of considerable interest. Given that such gas-phase reactions are initiated by double ionization and subsequently facilitated through deprotonation, we investigate the strong-field photodissociation of ethanethiol, also known as ethyl mercaptan, and compare it to results from ethanol. Contrary to expectations, the H3+ yield was found to be an order of magnitude lower for ethanethiol at certain laser field intensities, despite its lower ionization energy and higher acidity compared to ethanol. In-depth analysis of the femtosecond time-resolved experimental findings, supported by ab initio quantum mechanical calculations, provides key information regarding the roaming mechanisms related to H3+ formation. Results of this study on the dynamics of dissociative half-collisions involving H3+, a vital cation which acts as a Brønsted–Lowry acid protonating interstellar organic compounds, may also provide valuable information regarding the formation mechanisms and observed natural abundances of complex organic molecules in interstellar media and planetary atmospheres. [ABSTRACT FROM AUTHOR]