A study of the BrO and BrO2 radicals with vacuum ultraviolet photoelectron spectroscopy

Abstract

The BrO radical, prepared by the BrϩO 3 reaction, has been investigated by ultraviolet photoelectron spectroscopy. Two vibrationally resolved bands were observed corresponding to the ionizations BrO ϩ (X 3 ⌺ Ϫ )←BrO(X 2 ⌸) and BrO ϩ (a 1 ⌬)←BrO(X 2 ⌸). These assignments are supported by the results of complete active space self-consistent field/multireference configuration interaction ͑CASSCF/MRCI͒ calculations performed as part of this work. The adiabatic ionization energies of these bands were measured as (10.46Ϯ0.02) and (11.21Ϯ0.02)eV, respectively. Measurement of the vibrational separations in these bands led to estimates of the vibrational constants in the ionic states of (840Ϯ30) cm Ϫ1 and (880Ϯ30) cm Ϫ1 , and Franck-Condon simulations of the vibrational envelopes gave values of the ionic state bond lengths of (1.635Ϯ0.005) and (1.641Ϯ0.005) Å for the X 3 ⌺ Ϫ and a 1 ⌬ states of BrO ϩ , respectively. The OϩBr 2 reaction was found to give a band at (10.26Ϯ0.02) eV associated with a reaction product. Comparison of the results obtained for the BrϩO 3 reaction showed that it could not be assigned to ionization of BrO. Calculations of the first adiabatic ionization energies and Franck-Condon simulations of the vibrational envelopes of the first photoelectron bands of BrO 2 and Br 2 O and their isomers demonstrated that this band corresponds to the first ionization of OBrO, the BrO 2 ϩ (X 1 A 1 )←BrO 2 (X 2 B 1 ) ionization. FranckCondon simulations were performed with the experimental geometry of BrO 2 (X 2 B 1 ) but with different cationic state geometries. The simulated envelope which most closely matched the experimental envelope gave geometrical parameters of r e ϭ1.6135 Å and ЄOBrOϭ117.5°for the ionic state.

Ab initio study on the reaction mechanism of ozone with bromine atom

“…Ab initio studies on the reaction mechanism of Cl+O 3 →ClO+O 2 8 and F+O 3 →FO+O 2 9 have already been performed. The Br+O 3 reaction has been investigated by ultraviolet photoelectron spectroscopy, and the Br+O 3 reaction is exothermic by 32.3 kcal/mol 10. The rate constant of this reaction at 298 K is (1.2 ± 0.2) × 10 −12 cm 3 mol −1 s −1 11.…”

Photoionization studies of reactive intermediates using synchrotron radiation

“…By studying the Br + O3 reaction at short reaction times, using efficient pumping and electron detection methods, it proved possible to obtain sufficient concentrations of BrO to use PES to study its electronic structure and determine ionization energies to its low-lying ionic states. Also from the vibrationally resolved photoelectron bands, spectroscopic constants (equilibrium bond lengths, re, and vibrational constants ωe and ωexe ) were obtained for the ionic states (4).…”

Ab initio calculations and Franck–Condon analysis of photoelectron spectroscopy of CH3OO− and CD3OO−

“…With quantum chemical computing programs being readily available, geometries and normal modes of small to medium size molecules in different electronic states can now be calculated routinely. Based on these methods, numerous applications of FC calculations have been presented in the literature [1][2][3][4][5][6][7][8][9][10][11][12][13][14], and most of these studies just focus on the interpretation of experimentally known spectra. Because the geometry difference between two electronic states is a major factor that influences FC intensities, the simulation of vibronic spectra of ployatomic molecules can be regarded as a valuable test with respect to the quality of calculated geometries and as a starting point to obtain improved structures.…”

“…Because the geometry difference between two electronic states is a major factor that influences FC intensities, the simulation of vibronic spectra of ployatomic molecules can be regarded as a valuable test with respect to the quality of calculated geometries and as a starting point to obtain improved structures. In addition, spectral simulations of vibrational structure based on computed Franck-Condon factors (FCF) could provide fingerprint type identification of an observed spectrum, in terms of both the carrier and the electronic states in the transition (see, for examples, [9,10], and references therein). Also, it has been demonstrated that spectral simulations can be very useful in establishing vibrational assignments in an electronic spectrum observed with complex vibrational structure [1][2][3][4][5]7,10,11].…”