FIGURE 2 ATOMIC AND MOLECULAR PHYSICS, DILUTE MATTER, UNIVERSE SCIENCE SYNCHROTRON SOLEIL HIGHLIGHTS 2020 DESIRS BEAMLINE Associated publication Identifying isomers of peroxy radicals in the gas phase: 1-CHO vs. 2-CHO.3 32 27 7 X. Tang, X. Lin, G. A. Garcia, J.-C. Loison, Z. Gouid, H. H. Abdallah, C. Fittschen, M. Hochlaf, X. Gu, W. Zhang & L. Nahon. FIGURE 3 Chemical Communications 56, 15525 (2020). References [1] J. J. Orlando et al. , Chem. Soc. Rev. 41, 6294 (2012). [2] G. Meloni et al., J. Am. Chem. Soc. 128, 13559 (2006). [3] G. A. Garcia et al., J. Chem. Phys. 142, 164201 (2015). [4] X. Tang et al., J. Chem. Phys. 152, 104301 (2020). Corresponding author Xiaofeng Tang Hefei Institutes of Physical Science, In addition, the Franck-Condon factors for the ionization transitions of Chinese Academy of Sciences, Hefei, the two isomers 1-CHO and 2-CHO, from their neutral XA’’ ground2 Anhui 230031, China state to the cationic aA” excited state (the only one to be efficiently3 7 2 3 7 2 1 tangxf@aiofm.ac.cn populated via vertical transitions), have been calculated at the M062X/ aug-cc-pVTZ level. They indicate that only the GG, GT, G’G (for the2 2 21 1 1 Captions 1-CHO isomer) and G (for the 2-CHO) rotamers show favourable3 32 27 7 FIGURE 1: Synchrotron photoionization TOF mass Franck-Condon factors upon photoionization. The calculated photoelectron spectra and the corresponding m/z = 43 ion images spectra of these rotamers, obtained from their Franck-Condon factors, acquired (a) without and (b) with addition of oxygen into the flow tube. are presented in Figure 2 and show a very satisfactory agreement with the experimental global TPES, confirming the identification of the isomeric FIGURE 2: Threshold photoelectron spectrum of C3H7O2 distribution of the propylperoxy radical present in the reactor. Moreover, radical and its fitted calculated contribution of the various isomers/rotamers. the comparison between the fitted and experimental spectra confirm that the first two peaks of the TPES correspond to the aA” state of 2-CHO +1 FIGURE 3: Calculated stable structures of the isomers (Adiabatic Ionization Energy (AIE) = 9.759 ± 0.005 eV) and that of 1-CHO3 7 2 of the propylperoxy radical, together with their cations, + obtained at the (R)CCSD(T)-F12/aug-cc-pVDZ level of (AIE = 9.919 ± 0.005 eV). 3 7 2 theory. CONCLUSION The present study exemplifies the capabilities of iPEPICO complemented2 by advanced computations, as a powerful method able to provide new insights into on-line analysis of complex gas-phase chemical reactions, such as combustion processes and atmospheric oxidation, through isomer/ rotamer identification of elusive radical intermediates. The coincident ion kinetic energy distributions such as the ones presented here for the CH cation offer further analytical advantages to distinguish fragment+3 7 (dissociative ionization) from parent (direct ionization) ions. 61