Vacuum ultraviolet photochemistry of the conformers of the ethyl peroxy radical

Abstract

We study the conformers of the ethyl peroxy radical (C₂H₅O₂), the simplest peroxy radical having more than one conformer, by combining synchrotron radiation vacuum ultraviolet (VUV) photoionization mass spectrometry with theoretical calculations. The ethyl peroxy radical is formed in a microwave discharge flow tube through the reaction of the ethyl radical (C₂H₅) with oxygen molecules, where C₂H₅ is generated via the hydrogen-abstraction reaction of ethane with fluorine atoms. Two kinds of C₂H₅⁺, originating from photoionization of C₂H₅ and from dissociative photoionization of C₂H₅O₂, whose cation is not stable, have been identified and separated in photoionization mass spectra. The photoionization spectrum corresponding to C₂H₅O₂ is obtained and assigned with Franck–Condon calculations. The present findings show that the gauche conformer (G-C₂H₅O₂) of C₂H₅O₂ has favorable Franck–Condon factors in the ionization transitions, whereas the contribution of the trans conformer (T-C₂H₅O₂) to the photoionization spectrum is minor or negligible due to its large geometric changes in the photoionization process. Moreover, the reason for the instability of C₂H₅O₂⁺ and its detailed dissociation mechanisms have been unraveled with the aid of the calculated potential energy curves.