Threshold photoelectron spectroscopy of the HO2 radical

Abstract

We report a synchrotron radiation vacuum ultraviolet photoionization study of the hydroperoxyl radical (HO2), a key reaction intermediate in combustion and atmospheric chemistry as well as astrochemistry, using double imaging photoelectron photoion coincidence spectroscopy. The HO2 radical is formed in a microwave discharge flow tube reactor through a set of reactions initiated by F atoms in a CH4/O2/He gas mixture. The high-resolution threshold photoelectron spectrum of HO2 in the 11 eV–12 eV energy range is acquired without interferences from other species and assigned with the aid of theoretically calculated adiabatic ionization energies (AIEs) and Franck–Condon factors. The three vibrational modes of the radical cation HO2+, the H–O stretch, the H–O–O bend, and the O–O stretch, have been identified, and their individual frequencies are measured. In addition, the AIEs of the X3A″ ground state and the a1A′ first excited electronic state of HO2+ are experimentally determined at 11.359 ± 0.003 eV and 11.639 ± 0.005 eV, respectively, in agreement with high-level theoretically computed results. Furthermore, the former AIE value provides validation of thermochemical networks used to extract the enthalpy of formation of the HO2 radical.

Dimeric Product of Peroxy Radical Self-Reaction Probed with VUV Photoionization Mass Spectrometry and Theoretical Calculations: The Case of C2H5OOC2H5

“…The peak at m/z = 28 is assigned to the product C 2 H 4 . As the AIE of HO 2 is located at 11.359 eV [ 35 ], above the VUV lamp’s photon energies (hν = 10.0 and 10.6 eV), no signal of HO 2 radicals (m/z = 33) is observed in the photoionization mass spectrum. The mass peak at m/z = 32 is ascribed to O 2 + from the ionization of oxygen presented with a high concentration in the flow tube.…”

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

“…Note that the AIE of HO 2 locates at 11.359 eV, above the present photon energy, and thus no HO 2 radicals can be observed in the mass spectra. 40…”

“…Note that the AIE of HO 2 locates at 11.359 eV, above the present photon energy, and thus no HO 2 radicals can be observed in the mass spectra. 40 A previous study predicts that the reaction of the C 4 H 5 OO 2 peroxy radical with HO 2 has three channels, (R1a) C 4 H 5 OO 39 The alkoxy radical C 4 H 6 OClO formed from the self-reaction of C 4 H 6 OClO 2 or its bimolecular reaction with HO 2 can decompose to the stable product of chloroacetone (C 3 H 5 O 35 Cl and C 3 H 5 O 37 Cl) with a fast rate of B10 7 s À1 and has been completely consumed in the fast flow tube within the reaction time of B1 ms under the present experimental conditions. 39 Therefore, the signal of C 4 H 6 OClO (m/z = 121) is not observed in the photoionization mass spectrum of Fig.…”

Combined Modelling of Triply Paired Electronic States of HO2+ ion with 3 Symmetry using Coupled Eigen Model

“…The existing experimental informations for this ion are sparse and that too, pertaining to the ground electronic state of triplet multiplicity, focussing mainly on the accurate determination of OH stretching frequency of the ion in tagged state preferablywith He inert gas while the same frequency at free state was estimated with the uncertainty of about 5 cm −1 [13–15,17] . While this is being so, its neutral counterpart, HO 2 radical has significant amount of experimental [18–22] as well as theoretical investigation [23–26] …”

“…[4][5][6][7][8][9][10][11][12][13][14][15][16] The existing experimental informations for this ion are sparse and that too, pertaining to the ground electronic state of triplet multiplicity, focussing mainly on the accurate determination of OH stretching frequency of the ion in tagged state preferablywith He inert gas while the same frequency at free state was estimated with the uncertainty of about 5 cm À 1 . [13][14][15]17] While this is being so, its neutral counterpart, HO 2 radical has significant amount of experimental [18][19][20][21][22] as well as theoretical investigation. [23][24][25][26] The paper is organised as follows : After the introduction, a section is devoted to describe the details of a closed form analytical Eigen valued expressions capable of modelling a set of three electronic states interconnected via a running seam trajectory simultaneously across the multiple states.…”