PNNL

Abstract

This report details a photoelectron spectroscopy (PES) investigation on electron affinities (EAs) and electronic structures of several atmospherically relevant higher bromine and iodine oxide molecules in the gas phase. PES spectra of BrO2- and IO2- were recorded at 12 K and four photon energies--355 nm/3.496 eV, 266 nm/4.661 eV, 193 nm/6.424 eV, and 157 nm/7.867 eV--while BrO3-, IO3-, and IO4- were studied at 193 and 157 nm only due to their expected high electron binding energies. Spectral features corresponding to transitions from the anion ground state to the ground and excited states of the neutral are unraveled and resolved for each species. For the first time, EAs of these bromine and iodine oxides are experimentally determined (except for IO2) to be 2.515 ± 0.010 (BrO2), 2.575 ± 0.010 (IO2), 4.60 ± 0.05 (BrO3), 4.70 ± 0.05 (IO3), and 6.05 ± 0.05 eV (IO4). Three low-lying excited states with their respective excitation energies are obtained for BrO2 [1.69 (A 2B2), 1.79 (B 2A1), 1.99 eV (C 2A2)], BrO3 [0.7 (A 2A2), 1.6 (B2E), 3.1 eV (C 2E)], and IO3 [0.60 (A 2A2), 1.20 (B 2E), ~3.0 eV (C 2E)], whereas six excited states of IO2 are determined with the respective excitation energies of 1.63 (A 2B2), 1.73 (B 2A1), 1.83 (C 2A2), 4.23 (D 2A1), 4.63 (E 2B2), and 5.23 eV (F 2B1). Periodate possesses a very high electron binding energy. Only one excited state feature with 0.95 eV excitation energy is shown in the 157 nm spectrum. The obtained EAs and low-lying excited state information are compared with available theoretical calculations and discussed with their atmospheric implications.