Coupling of torsion and OH-stretching in tert-butyl hydroperoxide. I. The cold and warm first OH-stretching overtone spectrum

Anne S Hansen; Rachel M Huchmala; Emil Vogt; Mark A Boyer; Trisha Bhagde; Michael F Vansco; Casper V Jensen; Alexander Kjærsgaard; Henrik G Kjaergaard; Anne B McCoy; Marsha I Lester

doi:10.1063/5.0048020

Coupling of torsion and OH-stretching in tert-butyl hydroperoxide. I. The cold and warm first OH-stretching overtone spectrum

J Chem Phys. 2021 Apr 28;154(16):164306. doi: 10.1063/5.0048020.

Affiliations

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

PMID: 33940856
DOI: 10.1063/5.0048020

Abstract

The infrared (IR) spectrum of tert-butyl hydroperoxide (TBHP) in the region of the first OH-stretching overtone has been observed under jet-cooled and thermal (300 K, 3 Torr) conditions at ∼7017 cm^-1. The jet-cooled spectrum is recorded by IR multiphoton excitation with UV laser-induced fluorescence detection of OH radical products, while direct IR absorption is utilized under thermal conditions. Prior spectroscopic studies of TBHP and other hydroperoxides have shown that the OH-stretch and XOOH (X = H or C) torsion vibrations are strongly coupled, resulting in a double well potential associated with the torsional motion about the OO bond that is different for each of the OH-stretching vibrational states. A low barrier between the wells on the torsional potential results in tunneling split energy levels, which leads to four distinct transitions associated with excitation of the coupled OH-stretch-torsion states. In order to interpret the experimental results, two theoretical models are used that include the OH-stretch-torsion coupling in TBHP. Both methods are utilized to compute the vibrational transitions associated with the coupled OH-stretch-torsion states of TBHP, revealing the underlying transitions that compose the experimentally observed features. A comparison between theory and experiment illustrates the necessity for treatments that include OH-stretch and COOH torsion in order to unravel the spectral features observed in the first OH-stretching overtone region of TBHP.