A research team led by Prof. WANG Zhandong from the University of Science and Technology of China (USTC) of the Chinese Academy of Sciences (CAS) has made progress in low-temperature combustion research. The researchers realized the measurement and accurate quantitative analysis of the photoionization cross-section of organic hydroperoxides. The study was published in PNAS.

Organic hydrogen, as a key intermediate for the autoxidation of organic compounds, plays an important role in chain-branching reactions. However, the peroxides are highly reactive and elusive. As a result, the photoionization cross-section of the peroxide is difficult to measure and the chain-branching is hard to be quantitively analyzed. 

To meet the above challenges, the researchers developed a gentle and environmentally friendly alkyl peroxide synthesis method, and obtained 13 alkyl peroxides with different structures as standard samples. They established an experimental platform able to measure the photoionization cross-sections of those alkyl peroxides.

Furthermore, the researchers developed a chemical titration method combined with synchrotron vacuum ultraviolet-photoionization mass spectrometry (SVUV-PIMS) to measure the photoionization cross-section (PICS) of the carbonyl peroxide. Through experimental measurement and theoretical calculation, they found that the photodissociation of alkyl peroxides and carbonyl peroxides mainly occurs through the path of removing OOH, thus elucidating the “fingerprint” reaction channel of peroxide photodissociation. 

Based on this fingerprint, the researchers realized the accurate quantitative analysis of the chain-branching intermediates generated by the low-temperature combustion of pentane. In comparison with the experimental data, the simulation results based on the present state-of-the-art combustion model of alkanes overpredicted the formation temperature and the mole fraction of chain-branching intermediates, indicating the present kinetic model calls for further optimization.

The synthesis method and photoionization dataset for organic hydroperoxides are useful for the measurement and quantitative analysis of photoionization cross-sections of carbonyl peroxides in other fuel systems, which lay a foundation for the improvement of the kinetic model.