The emission bands of HO2 between 1·43 and 1·51 μm

The 2 A′ →2 A″ electronic spectrum of HO2 at 1·43 μm has been recorded at high resolution with a SISAM spectrometer. The analysis of the spectrum has yielded accurate molecular constants for the lowest vibrational level of the excited state. Emission is only observed from K′ ⩽ 2>; possible explanations for this phenomenon are discussed. Forbidden ΔK = 0 transitions are observed; the principal mechanism for their existence is believed to be a Renner-Teller interaction between the two electronic states. Vibrational hotbands of the type 2 A′ (v 1 v 2 v 3) →2 A″(v 1 v 2 v 3) are observed. New spectro-scopic information includes the three vibrational frequencies of the excited electronic state; the previous discrepancy in the value of ν3 is explained. The O-H stretching overtone band 2 A″(200) →2 A″(000) at 1·51 μm has also been recorded and analysed.