Electronic spectrum and structure of the HSO radical

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Abstract
A chemiluminescence spectrum in the range 5200–9600 Å is assigned to the 2A′–2Am’ transition of the HSO radical. The 0–0 band is observed at 6960 Å. The deuterated radical was also studied. The vibrational frequencies deduced from the vibronic transitions are ν′2(HSO) =828, ν″2(HSO) =1063, ν′2(DSO) =600±10, and ν″2(DSO) =770±10 for the bending vibration, and ν′3(HSO) =702±5 and ν″3(HSO) =1013±5 cm−1 for the SO bond stretch. The latter does not change significantly upon deuteration. The SH bond stretch ν1 is not manifested in the spectrum, and is assumed to come close to the SH group frequency of 2570 cm−1 in the electronic ground state. The frequency increases slightly upon excitation to the 2A′ state, as follows from the shift of the 0–0 band to 6958 cm−1 upon deuteration. Approximate bond lengths and angles of HSO in both electronic states are deduced from the partially resolved subband structure of the vibronic bands, which is compared with computed band contours. Relative Franck–Condon factors obtained from the intensities within the v″3 progressions are in accordance with an increase of the SO bond length from r″SO=1.54 to r′SO=1.69 Å. Emission from HSO (2A′) is observed up to v′3=7 in the system O/H2S/O3. Excitation is believed to occur through the chemiluminescent reaction SH+O3→SHO*+O2, leading to an upper limit of ΔH°f(HSO) ≲14.9 kcal/mole.