Vacuum ultraviolet photodynamics of the methyl peroxy radical studied by double imaging photoelectron photoion coincidences

Abstract

The vacuum ultraviolet (VUV) photoionization of the methyl peroxy radical, CH 3 O 2 , and unimolecular dissociation of internal energy selected CH 3 O 2 + cations were investigated in the 9.7-12.0 eV energy range by synchrotron-based double imaging photoelectron photoion coincidence (i 2 PEPICO). A microwave discharge flow tube was employed to produce CH 3 O 2 via the reaction of methyl radicals (CH 3) with oxygen gas. After identifying and separating the different sources of CH 3 + from photoionization of CH 3 or dissociative photoionization of CH 3 O 2 , the high resolution slow photoelectron spectrum (SPES) of CH 3 O 2 was obtained exhibiting two broad bands superimposed with a complex vibrational structure. The first band of the SPES is attributed to the X 3 A″ and a 1 A′ overlapped electronic states of CH 3 O 2 + and the second is assigned to the b 1 A′ electronic state with the help of theoretical calculations. The adiabatic ionization energy (AIE) of CH 3 O 2 is derived as 10.215 ± 0.015 eV, in good agreement with high-accuracy theoretical data from the literature. The vertical ionization energy of the b 1 A' electronic state is measured to be 11.5 eV and this state fully dissociates into CH 3 + and O 2 fragments. The 0 K adiabatic appearance energy (AE 0K) of the CH 3 + fragment ion is determined to be 11.1548 ± 0.020 eV.

Kinetics of 1- and 2-methylallyl + O2 reaction, investigated by photoionisation using synchrotron radiation

“…PEPICO has become a state-of-the-art detection tool for reactive species in the gas-phase. It has been used to investigate molecules involved in atmospheric, 33 combustion, 34 interstellar, 35,36 and catalytic processes. 37 Recently we reported a kinetic study on the allyl + O2 reaction, employing PEPICO.…”

Identifying isomers of peroxy radicals in the gas phase: 1-C3H7O2vs. 2-C3H7O2

“…A microwave discharge flow tube is employed as chemical reactor to model the low temperature oxidation of propane. 19,20 The two isomers, 1-C 3 H 7 O 2 and 2-C 3 H 7 O 2 , are clearly identified and assigned in the mass-selected threshold photoelectron spectrum (TPES) with the aid of their computed adiabatic ionization energies (AIEs) and Franck-Condon factors. The experimental and theoretical details can be found in the Supplementary Information.…”

Cl-Initiated oxidation of methacrolein under NOx-free conditions studied by VUV photoionization mass spectrometry

“…To get detailed information on the reaction system inside the fast flow tube, experiments were performed in sequence and can be divided into two parts. 32,33 Firstly, the experiment was performed without adding oxygen into the fast flow tube, and C 4 H 6 OCl and C 4 H 5 O radicals were formed from the Cl-addition reaction and the hydrogen abstraction reaction of MACR with Cl atoms, respectively. Then, with the addition of oxygen, the transient C 4 H 6 OCl and C 4 H 5 O radicals reacted with oxygen to produce peroxy radicals and these peroxy radicals could perform self-reactions or react with HO 2 radials in the flow tube under NO x -free conditions.…”