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O–H Stretch Overtone Excitation of Ethyl Hydroperoxide Conformers

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journal contribution
posted on 22.02.2016, 11:58 by Shizuka Hsieh, Thida Thida, Margaret K. Nyamumbo, Kelly A. Smith, Noah Naamad, Robert G. Linck
We present laser photoacoustic spectra of ethyl hydroperoxide (EHP) for 3–6 quanta of O–H stretch. Spectra are consistent with ab initio spectral simulations that take into account the influence of torsional motion about the O–O bond on O–H stretch overtone excitation. Experimental and simulated spectra share two trends. First, spectral features due to torsional excitation, including hot bands, become more prominent with increasing O–H stretch excitation, as has been shown previously for similar molecules such as methyl hydroperoxide. Second, contributions from the two different EHP conformers become clearly distinguishable at higher O–H stretch excitation, mainly due to the role of torsional motion. Results are consistent with a higher energy separation (330 cm–1) between the lower energy anti and the higher energy gauche conformers than predicted by electronic structure calculations (137 cm–1). Calculated absorption intensities are consistently higher than experimental values by ∼30% but within the experimental uncertainty. With each additional O–H stretch overtone, the dropoff in calculated integrated absorption intensities at room temperature becomes less extreme, with a 14-fold dropoff from 3νOH to 4νOH and an 8-fold decrease from 5νOH to 6νOH.