Spectroscopic probing and diagnostics of the geometric structure of the alkoxy and alkyl peroxy radical intermediates

Abstract

The recent spectroscopy of the small to moderate sized alkoxy and peroxy organic radicals is reviewed. Rotationally resolved laser induced fluorescence spectra of the alkoxy intermediates have been obtained in cold supersonic expansions. This rotational structure allows unambiguous assignment of observed spectral transitions to particular isomers and conformers of a given chemical species. Unfortunately the organic peroxy radicals have no excited electronic states that fluoresce. However there is an electronic transition in the near IR that gives rise to sharp absorption spectra, which can be detected using cavity ringdown spectroscopy. Since these experiments have been performed at room temperature, spectral congestion prevents the resolution of rotational structure. Nonetheless careful comparison between quantum chemistry calculations and the observed spectral origins and vibrational frequencies allow the probable assignment of many spectral bands to particular isomers and conformers. For both the alkoxy and peroxy radicals the analysed spectra provide a powerful diagnostic for monitoring their kinetics and dynamics.

Acknowledgements

The author gratefully acknowledges the support of the US National Science Foundation via grant CHE-0511809 and the financial support of the Chemical Sciences, Geosciences and Biosciences Division, Office of Basic Energy Sciences, Office of Science, US Department of Energy, via grant DE-FG02-01ER15172. The author also wishes to acknowledge the invaluable contribution of many of his students, including specifically, Christopher C. Carter, Sandhya Gopalakrishnan, Michael Pushkarsky, Sergey J. Zalyubovsky, Brent G. Glover, Jinjun Liu and Lily Zu.