Analysis of the electronic transition of the 2,1-hydroxypropylperoxy radical using cavity ringdown spectroscopy

The near infrared A ∼ – X ∼ electronic absorption spectrum of the 2,1-hydroxypropyl peroxy radical (2,1-HPP) has been recorded at room temperature by cavity ringdown spectroscopy. Twenty-five conformers of 2,1-HPP are predicted to exist as minima on the potential energy surface calculated via either ab initio or density functional theory. However, the experimental spectrum is explained in terms of the origin bands and vibrational structure of the three conformers predicted to be most stable. In addition to the OO stretch and COO bend bands typically observed in the A ∼ – X ∼ spectra of peroxy radicals, we attribute some observed bands to low-frequency fundamentals corresponding to the OOCC bending of 2,1-HPP. This assignment is supported by both Franck–Condon simulations and experiments on jet-cooled radicals.