Theoretical Study of the Low-Lying Electronically Excited States of OBrO

Abstract

Motivated by the possible importance of OBrO in atmospheric photochemistry, multireference configuration interaction calculations of the low-lying excited states were carried out to obtain information about the electronic vertical spectrum up to excitation energies of about 6 eV from the ground state, including the transition dipole moments, and about possible photodissociation pathways, based on one-dimensional cuts through the potential energy surfaces for dissociation into BrO + O and Br + O2, respectively. In addition, for probing the angle dependence the bending potentials were also calculated. From all computed eight doublet states (two/four of each symmetry in C 2 v C s ) only the 12A2 state at 2.7 eV possesses a large transition dipole moment with the 12B1 ground state, whereas for all other states this quantity is very small or zero. Therefore the 12A2 state should play a decisive role in OBrO photochemistry. Close to the 12A2 state two other states were found at 2.4 eV (12B2) and 2.5 eV (12A1) so that interactions of these three states should certainly influence possible dissociation processes. For this reason, besides direct adiabatic photodissociation of the 12A2 state into BrO + O also predissociation via these close-lying states can be expected, leading to a very complex photodissociation mechanism for excitation energies around 2.5 eV. Moreover, in this energy range photodissociation into Br + O2 is only possible through the 12B2 state (after initial excitation of the 12A2 state) because only for this state a small barrier of 0.7 eV relative to its minimum is estimated from the calculation of a simplified C 2 v minimum energy path. For the 12A1 and 12A2 states, rather large barriers are predicted. The next higher-lying states, with excitation energies of 3.9 eV (22A1) and 4.5 eV (22B2) are well separated from lower- and higher-lying states and from each other, but due to their small transition dipole moments, they should be probably of minor importance for the OBrO photochemistry. The last two states considered in our study are predicted to lie close together at 6.0 eV (22A2) and 6.1 eV (22B1) and are strongly repulsive upon dissociation into BrO + O. Finally, it should be noted that our calculations demonstrate the expected qualitative similarity to the results previously obtained for the corresponding OClO system.

Inhibition of hydrogen oxidation by HBr and Br2

“…In addition, single-reference methods (which may, at least in principle, attain chemical accuracy) suffer from severe spin-contamination for BrOO and in general produce unusable results. The ATcT values for the triatomic bromine oxides, given in Table 1, are based on the two mentioned experimental determinations related to BrOBr and the best available theoretical results [74,89,[95][96][97][98], which were also included in the TN.…”

Environmental effects of large igneous province magmatism: a Siberian perspective

“…The rate constant for O + OH is a fit to three temperature dependence studies: Westenberg et al [1448], Lewis and Watson [817], and Howard and Smith [609]. This recommendation is consistent with earlier work near room temperature as reviewed by Lewis and Watson [817] and with the measurements of Brune et al [185], Smith and Stewart [1215] and Robertson and Smith [1121]. The ratio k(O + HO 2 )/k(O + OH) measured by Keyser [708] agrees with the rate constants recommended here.…”

“…In Table 4-141 are listed the averages over 1-nm intervals of the spectrum measured at a resolution of 0.66 nm. No quantum yields are available, but theoretical calculations by Vetter et al [817] indicate that photodissociation occurs via BrO + O( …”

Photoelectron spectroscopy of higher bromine and iodine oxide anions: Electron affinities and electronic structures of BrO2,3 and IO2–4 radicals

“…32-36 Inspired by wellresolved UV/Vis absorption spectra, 25,30,31 high-level ab initio calculations on the ground, as well as the low-lying excited states, have been reported. 31,37,38 Despite these impressive progresses, the low-lying excited states of A( 2 B 2 ) and B( 2 A 1 ) predicted to be in the proximity of C( 2 A 2 ) (Ref. 38) have not yet been probed experimentally due to extremely small dipole transitions from the ground X( 2 B 1 ) state.…”

“…31,37,38 Despite these impressive progresses, the low-lying excited states of A( 2 B 2 ) and B( 2 A 1 ) predicted to be in the proximity of C( 2 A 2 ) (Ref. 38) have not yet been probed experimentally due to extremely small dipole transitions from the ground X( 2 B 1 ) state. Being similar to ClO 2 , 6, 7 the photochemistry and photodissociation of BrO 2 and hence its atmospheric implications are expected to involve all three closed-lying states via spin-orbit and vibronic interactions following photoexcitation to C( 2 A 2 ).…”