Organic peroxy radicals (RO2) are important intermediates in the degradation of atmospheric volatile organic compounds (VOCs). RO2 not only participates in the chain cycles of atmospheric radicals and influences oxidizing capacity of the atmosphere, but also controls the formation of secondary pollutants. Under low NOx conditions, peroxy radicals react mainly with HO2 radicals, as well as with themselves, and their products tend to have low volatility easily entering the particulate phase. However, the associated double radical reactions are complex, the chemical mechanisms are poorly understood and experimental and theoretical studies are extremely challenging.
Recently, a collaborated team headed by Prof. Weijun Zhang from Hefei Institutes of Physical Science (HFIPS) of the Chinese Academy of Sciences (CAS) studied the self-reaction of ethyl peroxy radicals (C2H5O2). In this process, they combined advanced vacuum ultraviolet (VUV) photoionization mass spectrometry with theoretical calculations, which provided a new insight into the direct measurement of the elusive dimeric product Organic peroxides (ROOR).
The results have been reported in International Journal of Molecular Sciences.
Together with scientists from Université de Lille, France, the team investigated the self-reactions of ethyl peroxy radical (C2H5O2). In addition to the main products CH3CHO, C2H5OH, C2H5O and C2H5OOH, the dimeric product C2H5OOC2H5 from self-reaction of C2H5O2 was clearly observed for the first time in VUV photoionization mass spectrum.
The kinetic experiments of self-reaction of C2H5O2 and theoretical calculations were performed to verify the reaction mechanism of the ROOR product channel. Also, the adiabatic ionization energy of C2H5OOC2H5 was determined by measuring the synchrotron photoionization efficiency spectrum. Combined with Franck-Condon factor simulations, the neutral and ionic structures of C2H5OOC2H5 were revealed.
"Our study demonstrated that the ROOR product channel is not negligible in the small RO2 self-reactions," said LIN Xiaoxiao, member of the team.
VUV lamp photoionization mass spectra measured (a) without O2 and (b) with O2 in the microwave discharge flow tube, with 5 times magnified data in red. (Image by LIN Xiaoxiao)
Photoionization spectrum of C2H5OOC2H5 and its calculated results in red. (Image by LIN Xiaoxiao)
Dimeric Product of Peroxy Radical Self-Reaction Probed with VUV Photoionization Mass Spectrometry and Theoretical Calculations: The Case of C2H5OOC2H5