Peroxy radicals are chemicals that play a vital role as reaction intermediates in the oxidation of atmospheric chemistry and combustion.
Real-time detection of key species in the oxidation reactions by photoionization mass spectrometry. Image Credit: Xiaoxiao Lin.
They can react to produce a lot of secondary pollutants like ozone and secondary organic aerosols. Thus, they have had a huge impact on the atmospheric environment and human health, thereby gaining widescale attention in the last few decades.
Specifically, the increase in the mass of peroxy radicals makes their structure complex, often taking various isomers or conformers. The isomers or conformers of peroxy radicals are not well understood. Thus, they have been very difficult to identify.
A team of researchers headed by Prof. Weijun Zhang from the Hefei Institutes of Physical Science (HFIPS) of the Chinese Academy of Sciences (CAS) has analyzed ethyl peroxy radical’s vacuum ultraviolet (VUV) photochemistry and found its conformers. The study has been reported in Physical Chemistry Chemical Physics.
The researchers collaborated with colleagues from the National Synchrotron Radiation Laboratory to investigate C2H5O2, the VUV photoionization of ethyl peroxy radical, which was also the simplest peroxy radical with more than one conformer.
They used a homemade photoionization time-of-flight mass spectrometer at Hefei synchrotron to complement the experiment with theoretical calculations.
A microwave discharge flow tube was used as the reactor to synthesize the C2H5O2 radical through the reaction of C2H5 with oxygen molecules. The researchers identified and pinpointed a range of radicals involved in the oxidation reaction by using the online photoionization mass spectra.
Moreover, they observed the photoionization spectrum of C2H5O2 and assigned it with theoretical Franck–Condon (FC) calculations. The outcomes demonstrate that the gauche conformer, or G-C2H5O2, of C2H5O2 exhibits an ideal FC factor in the ionization transitions. By contrast, its trans-conformer, or T-C2H5O2, does not contribute much 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.
Xiaofeng Tang, Study Researcher, Hefei Institutes of Physical Science, Chinese Academy of Sciences
The study was financially supported by the National Natural Science Foundation of China, the International Partnership Program of CAS, and the Key Program of Research and Development of Hefei Science Center of CAS.
Journal Reference:
Wen, Z., et al. (2021) Vacuum ultraviolet photochemistry of the conformers of the ethyl peroxy radical. Physical Chemistry Chemical Physics. doi.org/10.1039/D1CP02655K.