Coupling of torsion and OH-stretching in tert-butyl hydroperoxide. II. The OH-stretching fundamental and overtone spectra

Emil Vogt; Rachel M Huchmala; Casper V Jensen; Mark A Boyer; Jens Wallberg; Anne S Hansen; Alexander Kjærsgaard; Marsha I Lester; Anne B McCoy; Henrik G Kjaergaard

doi:10.1063/5.0048022

Coupling of torsion and OH-stretching in tert-butyl hydroperoxide. II. The OH-stretching fundamental and overtone spectra

J Chem Phys. 2021 Apr 28;154(16):164307. doi: 10.1063/5.0048022.

Affiliations

¹ Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen, Denmark.
² Department of Chemistry, University of Washington, Seattle, Washington 98195-1700, USA.
³ Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, USA.

PMID: 33940839
DOI: 10.1063/5.0048022

Abstract

The vibrational spectra of gas phase tert-butyl hydroperoxide have been recorded in the OH-stretching fundamental and overtone regions (Δv_OH = 1-5) at room temperature using conventional Fourier transform infrared (Δv_OH = 1-3) and cavity ring-down (Δv_OH = 4-5) spectroscopy. In hydroperoxides, the OH-stretching and COOH torsion vibrations are strongly coupled. The double-well nature of the COOH torsion potential leads to tunneling splitting of the energy levels and, combined with the low frequency of the torsional vibration, results in spectra in the OH-stretching regions with multiple vibrational transitions. In each of the OH-stretching regions, both an OH-stretching and a stretch-torsion combination feature are observed, and we show direct evidence for the tunneling splitting in the OH-stretching fundamental region. We have developed two complementary vibrational models to describe the spectra of the OH-stretching regions, a reaction path model and a reduced dimensional local mode model, both of which describe the features of the vibrational spectra well. We also explore the torsional dependence of the OH-stretching transition dipole moment and show that a Franck-Condon treatment fails to capture the intensity in the region of the stretch-torsion combination features. The accuracy of the Franck-Condon treatment of these features improves with increasing Δv_OH.