Vacuum ultraviolet photochemistry of the conformers of the ethyl peroxy radical.

We study the conformers of the ethyl peroxy radical (CHO), 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 (CH) with oxygen molecules, where CH is generated the hydrogen-abstraction reaction of ethane with fluorine atoms. Two kinds of CH, originating from photoionization of CH and from dissociative photoionization of CHO, whose cation is not stable, have been identified and separated in photoionization mass spectra. The photoionization spectrum corresponding to CHO is obtained and assigned with Franck-Condon calculations. The present findings show that the conformer (-CHO) of CHO has favorable Franck-Condon factors in the ionization transitions, whereas the contribution of the conformer (-CHO) 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 CHO and its detailed dissociation mechanisms have been unraveled with the aid of the calculated potential energy curves.