The effect of torsion - vibration couplings on the ν9 and ν1 bands in the CH3OO· radical

Huang, Meng

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https://hdl.handle.net/2142/97174 Copy

Description

Title

The effect of torsion - vibration couplings on the ν9 and ν1 bands in the CH3OO· radical

Author(s)

Huang, Meng

Contributor(s)

• McCoy, Anne B.
• Miller, Terry A.

Issue Date

2017-06-20

Keyword(s)

• Large amplitude motions
• Internal rotation

Abstract

There are three CH stretch modes in the CH${_3}$OO${cdot}$, namely the totally symmetric stretch, $nu_2$, the out-of-phase symmetric stretch, $nu_1$, and the antisymmetric stretch, $nu_9$. However, only two strong partially rotationally resolved vibrational transitions are observed in the CH stretch region of the infrared spectrum of CH${_3}$OO${cdot}$. Moreover, the Q-branches of both bands are significantly broader than the simulations using an asymmetric rigid rotor model. Previously, the rotational contour of the ${nu_2}$ band in the experimental spectrum has been simulated by considering the fundamental as well as sequence band transitions involving torsionally excited levels populated at room temperaturefootnote{K.-H.~Hsu, Y.-H.~Huang, Y.-P.~Lee, M.~Huang, T.~A.~Miller and A.~B.~McCoy textit{J.~Phys.~Chem.~A}, 2016, 120 (27), 4827}. Using a four dimension Hamiltonian that involves the three CH stretches and the CH${_3}$ torsion, the torsional sequence bands of the ${nu_2}$ stretch were calculated to be slightly shifted from the origin band as a result of the couplings between the CH stretches and CH${_3}$ torsion which are particularly large due to an accidental degeneracy between the combination level involving the ${nu_2}$ stretch and $n$ quanta in the CH${_3}$ torsion and the combination level involving the ${nu_1}$ or ${nu_9}$ stretch and $n-1$ quanta in the CH${_3}$ torsion. In this study we focus on the part of CH${_3}$OO${cdot}$ vibrational spectrum containing the $nu_1$ and $nu_9$ bands. Along with the 4-dimensional Hamiltonian which was used to simulate the spectra in the $nu_2$ region, we analyze the effect of torsion-stretch couplings on the ${nu_1}$ and ${nu_9}$ bands based on the model developed by Hougenfootnote{J.-T.~Hougen textit{J.~Mol.~Spec.}, 2001, 207, 60} to describe methanol. To account for the accidental degeneracies in CH$_3$OO, we extend the previous model to include the combination levels involving the ${nu_2}$ stretch and the CH${_3}$ torsion. Unlike the torsional sequence bands and fundamental of $nu_2$, the tunneling splittings of the torsional sequence bands and fundamentals of $nu_1$ and $nu_9$ have different signs, which results in the weak intensity of $nu_1$ fundamental and broadening in the rotational contour of the torsional sequence bands of $nu_9$.The simulation of the $nu_9$ and $nu_1$ bands including the torsional sequence bands using the parameters which are consistent with the ones used in the simulation of the $nu_2$ band is in good agreement with the experimental spectrum.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

text

Language

eng

Permalink

http://hdl.handle.net/2142/97174

DOI

https://doi.org/10.15278/isms.2017.TD04

Copyright and License Information

Copyright 2017 Meng Huang

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