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Title: Infrared laser spectroscopy of the n-propyl and i-propyl radicals: Stretch-bend Fermi coupling in the alkyl CH stretch region

Journal Article · · Journal of Chemical Physics
DOI:https://doi.org/10.1063/1.4971239· OSTI ID:1409063

The n-propyl and i-propyl radicals were generated in the gas phase via pyrolysis of n-butyl nitrite [CH3(CH2)3ONO] and i-butyl nitrite [(CH3)2CHCH2ONO], respectively. Nascent radicals were promptly solvated by a beam of He nanodroplets, and the infrared spectra of the radicals were recorded in the CH stretching region. Several previously unreported bands are observed between 2800 and 3150 cm–1. The CH stretching modes observed above 3000 cm–1 are in excellent agreement with CCSD(T) anharmonic frequencies computed using second-order vibrational perturbation theory. However, between 2800 and 3000 cm–1, the spectra of n- and i-propyl radicals become congested and difficult to assign due to the presence of multiple anharmonic resonance polyads. To model the spectrally congested region, Fermi and Darling-Dennison resonances are treated explicitly using “dressed” Hamiltonians and CCSD(T) quartic force fields in the normal mode representation, and the agreement with experiment is less than satisfactory. Computations employing local mode effective Hamiltonians reveal the origin of the spectral congestion to be strong coupling between the high frequency CH stretching modes and the lower frequency CHn bending/scissoring motions. The most significant coupling is between stretches and bends localized on the same CH2/CH3 group. As a result, spectral simulations using the local mode approach are in excellent agreement with experiment.

Research Organization:
Univ. of Georgia, Athens, GA (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences, and Biosciences Division
Grant/Contract Number:
SC0008086; AC02-05CH11231; FG02-12ER16298; FG02-97ER14748
OSTI ID:
1409063
Alternate ID(s):
OSTI ID: 1335712
Journal Information:
Journal of Chemical Physics, Vol. 145, Issue 22; ISSN 0021-9606
Publisher:
American Institute of Physics (AIP)Copyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 18 works
Citation information provided by
Web of Science

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Cited By (3)

Teaching vibrational spectra to assign themselves journal January 2018
tert -Butyl peroxy radical: ground and first excited state energetics and fundamental frequencies journal January 2019
Modeling vibrational anharmonicity in infrared spectra of high frequency vibrations of polyatomic molecules journal March 2019

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