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

Abstract

The BrO radical, prepared by the Br+O3 reaction, has been investigated by ultraviolet photoelectron spectroscopy. Two vibrationally resolved bands were observed corresponding to the ionizations BrO+(X 3Σ−)←BrO(X 2Π) and BrO+(a 1Δ)←BrO(X 2Π). These assignments are supported by the results of complete active space self-consistent field/multireference configuration interaction (CASSCF/MRCI) calculations performed as part of this work. The adiabatic ionization energies of these bands were measured as (10.46±0.02) and (11.21±0.02)eV, respectively. Measurement of the vibrational separations in these bands led to estimates of the vibrational constants in the ionic states of (840±30) cm−1 and (880±30) cm−1, and Franck–Condon simulations of the vibrational envelopes gave values of the ionic state bond lengths of (1.635±0.005) and (1.641±0.005) Å for the X 3Σ− and a 1Δ states of BrO+, respectively. The O+Br2 reaction was found to give a band at (10.26±0.02) eV associated with a reaction product. Comparison of the results obtained for the Br+O3 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 BrO2 and Br2O and their isomers demonstrated that this band corresponds to the first ionization of OBrO, the BrO2+(X 1A1)←BrO2(X 2B1) ionization. Franck–Condon simulations were performed with the experimental geometry of BrO2(X̃ 2B1) but with different cationic state geometries. The simulated envelope which most closely matched the experimental envelope gave geometrical parameters of re=1.6135 Å and ∠OBrO=117.5° for the ionic state.