Observation of the Ã−X̃ Electronic Transition of the β-Hydroxyethylperoxy Radical

The Ã−X̃ electronic absorption spectrum of β-hydroxyethyl peroxy radical (β-HEP) has been recorded in the NIR by cavity ringdown spectroscopy. The precursor, β-hydroxyethyl radical, is generated by photolysis of 2-iodoethanol and by OH-initiated oxidation of ethene, in both cases followed by addition of O₂ to form the peroxy. Although electronic structure calculations predict that 13 conformers of β-HEP exist as minima on the potential energy surface, the experimental spectrum is rationalized in terms of the band origins and vibrational progressions of only the two most stable conformers, G₁G₂G₃ and G₁^′G₂G<sub>3