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

Franke, Peter R.; Tabor, Daniel P.; Moradi, Christopher P.; Douberly, Gary E.; Agarwal, Jay; Schaefer, III, Henry F.; Sibert, Edwin L.

doi:10.1063/1.4971239

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

Journal Article · Tue Dec 13 00:00:00 EST 2016 · Journal of Chemical Physics

DOI:https://doi.org/10.1063/1.4971239· OSTI ID:1409063

Franke, Peter R. ^[1]; ^[2]; Moradi, Christopher P. ^[3]; ^[3]; Agarwal, Jay ^[3]; Schaefer, III, Henry F. ^[3]; ^[2]

Univ. of Georgia, Athens, GA (United States); University of Georgia, Athens, GA
Univ. of Wisconsin-Madison, Madison, WI (United States)
Univ. of Georgia, Athens, GA (United States)

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 CH_n 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.

View Accepted Manuscript (DOE)

Research Organization:: Univ. of Georgia Research Foundation, Athens, GA (United States)

Sponsoring Organization:: USDOE; USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Chemical Sciences, Geosciences & Biosciences Division

Grant/Contract Number:: AC02-05CH11231; FG02-97ER14748; SC0008086

OSTI ID:: 1409063

Alternate ID(s):: OSTI ID: 1335712

Journal Information:: Journal of Chemical Physics, Journal Name: Journal of Chemical Physics Journal Issue: 22 Vol. 145; ISSN JCPSA6; ISSN 0021-9606

Publisher:: American Institute of Physics (AIP)Copyright Statement

Country of Publication:: United States

Language:: English

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