Peroxy radicals (RO2) are very important reaction intermediates in the oxidation of atmospheric chemistry and combustion. Their reactions can lead to the formation of a great deal of secondary pollutants, such as ozone and secondary organic aerosols, taking a large influence on the atmospheric environment and human health and attracting attentions in the past decades. In particular, with the increase of their mass, the structure of peroxy radicals becomes complex, usually taking several isomers or conformers. The knowledge on the isomers or conformers of peroxy radicals is very limited, and identifying them is still a challenge.
A research group led by Prof. ZHANG Weijun at Hefei Institutes of Physical Science (HFIPS), Chinese Academy of Sciences (CAS), has made new progresses in the vacuum ultraviolet photochemistry of the ethyl peroxy radical.
The research paper has already been published in Physical Chemistry Chemical Physics.
Together with the National Synchrotron Radiation Laboratory (NSRL), the team investigated C2H5O2, the vacuum ultraviolet (VUV) photoionization of the ethyl peroxy radical, which was also the simplest peroxy radical having more than one conformer. By using a home-made photoionization time-of-flight mass spectrometer at Hefei synchrotron, researchers complemented the experiment with theoretical calculations.
A microwave discharge flow tube was employed as reactor to produce the C2H5O2 radical via the reaction of C2H5 with oxygen molecules. Many kinds of radicals involved in the oxidation reaction was identified and determined in the online photoionization mass spectra.
In addition, the photoionization spectrum of C2H5O2 was observed and assigned with theoretical Franck–Condon (FC) calculations. The results show that the gauche conformer (G-C2H5O2) of C2H5O2 has favorable FC factor in the ionization transitions, while the trans conformer (T-C2H5O2) contributes little to the photoionization spectrum.
"This work provides important data and technical methods for online detection of different kinds of peroxy radicals plus their isomers and conformers," said TANG Xiaofeng, a member of the team.
The work was supported by the National Natural Science Foundation of China, the International Partnership Program of Chinese Academy of Sciences and the Key Program of Research and Development of Hefei Science Center, CAS.
Fig. 1 Real-time detection of key species in the oxidation reactions by photoionization mass spectrometry. (Image by LIN Xiaoxiao)
Fig. 2 The optimized structures of the gauche and the trans conformers of C2H5O2 and their cations. (Image by LIN Xiaoxiao)
Hefei Institutes of Physical Science (http://english.hf.cas.cn/)