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Title: Propargyl + O2 Reaction in Helium Droplets: Entrance Channel Barrier or Not?

Abstract

A combination of liquid He droplet experiments and multireference electronic structure calculations is used to probe the potential energy surface for the reaction between the propargyl radical and O2. Infrared laser spectroscopy is used to probe the outcome of the low temperature, liquid He-mediated reaction. Bands in the spectrum are assigned to the acetylenic CH stretch (ν1), the symmetric CH2 stretch (ν2), and the antisymmetric CH2 stretch (ν13) of the trans-acetylenic propargyl peroxy radical (•OO—CH2—C≡CH). The observed band origins are in excellent agreement with previously reported anharmonic frequency computations for this species. The Stark spectrum of the ν1 band provides further evidence that the reaction leads only to the trans-acetylenic species. There are no other bands in the CH2 stretching region that can be attributed to any of the other three propargyl peroxy isomers/conformers that are predicted to be minimum energy structures (gauche-acetylenic, cis-allenic, and trans-allenic). There is also no evidence for the kinetic stabilization of a van der Waals complex between propargyl and O2. A combination of multireference and coupled-cluster electronic structure calculations is used to probe the potential energy surface in the neighborhood of the transition state connecting reactants with the acetylenic adduct. The multireference based evaluation ofmore » the doublet-quartet splitting added to the coupled-cluster calculated quartet state energies yields what are likely the most accurate predictions for the doublet potential curve. As a result, this calculation suggests that there is no saddle point for the addition process, in agreement with the experimental observations. Other calculations suggest the possible presence of a small submerged barrier.« less

Authors:
 [1];  [1];  [2];  [2]; ORCiD logo [1]
  1. Univ. of Georgia, Athens, GA (United States)
  2. Argonne National Lab. (ANL), Argonne, IL (United States)
Publication Date:
Research Org.:
Univ. of Georgia Research Foundation, Athens, GA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Chemical Sciences, Geosciences & Biosciences Division
OSTI Identifier:
1409049
Grant/Contract Number:  
SC0008086
Resource Type:
Accepted Manuscript
Journal Name:
Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory
Additional Journal Information:
Journal Volume: 117; Journal Issue: 50; Journal ID: ISSN 1089-5639
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

Moradi, Christopher P., Morrison, Alexander M., Klippenstein, Stephen J., Goldsmith, C. Franklin, and Douberly, Gary E. Propargyl + O2 Reaction in Helium Droplets: Entrance Channel Barrier or Not?. United States: N. p., 2013. Web. doi:10.1021/jp407652f.
Moradi, Christopher P., Morrison, Alexander M., Klippenstein, Stephen J., Goldsmith, C. Franklin, & Douberly, Gary E. Propargyl + O2 Reaction in Helium Droplets: Entrance Channel Barrier or Not?. United States. doi:10.1021/jp407652f.
Moradi, Christopher P., Morrison, Alexander M., Klippenstein, Stephen J., Goldsmith, C. Franklin, and Douberly, Gary E. Mon . "Propargyl + O2 Reaction in Helium Droplets: Entrance Channel Barrier or Not?". United States. doi:10.1021/jp407652f. https://www.osti.gov/servlets/purl/1409049.
@article{osti_1409049,
title = {Propargyl + O2 Reaction in Helium Droplets: Entrance Channel Barrier or Not?},
author = {Moradi, Christopher P. and Morrison, Alexander M. and Klippenstein, Stephen J. and Goldsmith, C. Franklin and Douberly, Gary E.},
abstractNote = {A combination of liquid He droplet experiments and multireference electronic structure calculations is used to probe the potential energy surface for the reaction between the propargyl radical and O2. Infrared laser spectroscopy is used to probe the outcome of the low temperature, liquid He-mediated reaction. Bands in the spectrum are assigned to the acetylenic CH stretch (ν1), the symmetric CH2 stretch (ν2), and the antisymmetric CH2 stretch (ν13) of the trans-acetylenic propargyl peroxy radical (•OO—CH2—C≡CH). The observed band origins are in excellent agreement with previously reported anharmonic frequency computations for this species. The Stark spectrum of the ν1 band provides further evidence that the reaction leads only to the trans-acetylenic species. There are no other bands in the CH2 stretching region that can be attributed to any of the other three propargyl peroxy isomers/conformers that are predicted to be minimum energy structures (gauche-acetylenic, cis-allenic, and trans-allenic). There is also no evidence for the kinetic stabilization of a van der Waals complex between propargyl and O2. A combination of multireference and coupled-cluster electronic structure calculations is used to probe the potential energy surface in the neighborhood of the transition state connecting reactants with the acetylenic adduct. The multireference based evaluation of the doublet-quartet splitting added to the coupled-cluster calculated quartet state energies yields what are likely the most accurate predictions for the doublet potential curve. As a result, this calculation suggests that there is no saddle point for the addition process, in agreement with the experimental observations. Other calculations suggest the possible presence of a small submerged barrier.},
doi = {10.1021/jp407652f},
journal = {Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory},
number = 50,
volume = 117,
place = {United States},
year = {2013},
month = {9}
}

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