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Title: Infrared Spectroscopy of the Tropyl Radical in Helium Droplets

Abstract

Here, the infrared spectrum of the $$\tilde{X}$$ 2E 2" tropyl radical has been recorded in the range of the CH-stretch vibrational modes using the helium droplet isolation technique. Two bands are observed at 3053 and 3058 cm –1. The electronic degeneracy of the ground state results in a Jahn–Teller interaction for two of the CH-stretch modes, i.e., first-order interaction for E 3' symmetry modes and second-order interaction for E 2' symmetry modes. The experimentally observed bands are assigned to the E 1' and E 3' CH-stretch modes. The E 1' mode is infrared-active, whereas the E 3' mode is inactive in the absence of the Jahn–Teller interaction. The transition to the upper component of the Jahn–Teller split E 3' mode gains intensity via vibronic coupling, giving rise to the second experimentally observed band.

Authors:
 [1];  [1];  [1];  [2]; ORCiD logo [2]
  1. Ruhr-Univ. Bochum, Bochum (Germany)
  2. Univ. of Georgia, Athens, GA (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)
OSTI Identifier:
1409059
Grant/Contract Number:
SC0008086
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory
Additional Journal Information:
Journal Volume: 120; Journal Issue: 34; 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

Kaufmann, Matin, Leicht, Daniel, Havenith, Martina, Broderick, Bernadette M., and Douberly, Gary E. Infrared Spectroscopy of the Tropyl Radical in Helium Droplets. United States: N. p., 2016. Web. doi:10.1021/acs.jpca.6b06522.
Kaufmann, Matin, Leicht, Daniel, Havenith, Martina, Broderick, Bernadette M., & Douberly, Gary E. Infrared Spectroscopy of the Tropyl Radical in Helium Droplets. United States. doi:10.1021/acs.jpca.6b06522.
Kaufmann, Matin, Leicht, Daniel, Havenith, Martina, Broderick, Bernadette M., and Douberly, Gary E. Tue . "Infrared Spectroscopy of the Tropyl Radical in Helium Droplets". United States. doi:10.1021/acs.jpca.6b06522. https://www.osti.gov/servlets/purl/1409059.
@article{osti_1409059,
title = {Infrared Spectroscopy of the Tropyl Radical in Helium Droplets},
author = {Kaufmann, Matin and Leicht, Daniel and Havenith, Martina and Broderick, Bernadette M. and Douberly, Gary E.},
abstractNote = {Here, the infrared spectrum of the $\tilde{X}$2E2" tropyl radical has been recorded in the range of the CH-stretch vibrational modes using the helium droplet isolation technique. Two bands are observed at 3053 and 3058 cm–1. The electronic degeneracy of the ground state results in a Jahn–Teller interaction for two of the CH-stretch modes, i.e., first-order interaction for E3' symmetry modes and second-order interaction for E2' symmetry modes. The experimentally observed bands are assigned to the E1' and E3' CH-stretch modes. The E1' mode is infrared-active, whereas the E3' mode is inactive in the absence of the Jahn–Teller interaction. The transition to the upper component of the Jahn–Teller split E3' mode gains intensity via vibronic coupling, giving rise to the second experimentally observed band.},
doi = {10.1021/acs.jpca.6b06522},
journal = {Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory},
number = 34,
volume = 120,
place = {United States},
year = {Tue Aug 16 00:00:00 EDT 2016},
month = {Tue Aug 16 00:00:00 EDT 2016}
}

Journal Article:
Free Publicly Available Full Text
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Cited by: 1work
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  • Here, the entrance channel complex in the exothermic OH + CH 4 → H 2O + CH 3 reaction has been isolated in helium nanodroplets following the sequential pick-up of the hydroxyl radical and methane. The a-type OH stretching band was probed with infrared depletion spectroscopy, revealing a spectrum qualitatively similar to that previously reported in the gas phase, but with additional substructure that is due to the different internal rotation states of methane (j CH4 = 0, 1, or 2) in the complex. We fit the spectra by assuming the rotational constants of the complex are the same formore » all internal rotation states; however, subband origins are found to decrease with increasing j CH4. Measurements of deuterated complexes have also been made (OD–CH 4, OH–CD 4, and OD–CD 4), the relative linewidths of which provide information about the flow of vibrational energy in the complexes; vibrational lifetime broadening is prominent for OH–CH 4 and OD–CD 4, for which the excited OX stretching state has a nearby CY 4 stretching fundamental (X, Y = H or D).« less
  • Cycloheptatrienyl (tropyl) radical, C{sub 7}H{sub 7}, was cleanly produced in the gas-phase, entrained in He or Ne carrier gas, and subjected to a set of flash-pyrolysis micro-reactors. The pyrolysis products resulting from C{sub 7}H{sub 7} were detected and identified by vacuum ultraviolet photoionization mass spectrometry. Complementary product identification was provided by infrared absorption spectroscopy. Pyrolysis pressures in the micro-reactor were roughly 200 Torr and residence times were approximately 100 μs. Thermal cracking of tropyl radical begins at 1100 K and the products from pyrolysis of C{sub 7}H{sub 7} are only acetylene and cyclopentadienyl radicals. Tropyl radicals do not isomerize tomore » benzyl radicals at reactor temperatures up to 1600 K. Heating samples of either cycloheptatriene or norbornadiene never produced tropyl (C{sub 7}H{sub 7}) radicals but rather only benzyl (C{sub 6}H{sub 5}CH{sub 2}). The thermal decomposition of benzyl radicals has been reconsidered without participation of tropyl radicals. There are at least three distinct pathways for pyrolysis of benzyl radical: the Benson fragmentation, the methyl-phenyl radical, and the bridgehead norbornadienyl radical. These three pathways account for the majority of the products detected following pyrolysis of all of the isotopomers: C{sub 6}H{sub 5}CH{sub 2}, C{sub 6}H{sub 5}CD{sub 2}, C{sub 6}D{sub 5}CH{sub 2}, and C{sub 6}H{sub 5}{sup 13}CH{sub 2}. Analysis of the temperature dependence for the pyrolysis of the isotopic species (C{sub 6}H{sub 5}CD{sub 2}, C{sub 6}D{sub 5}CH{sub 2}, and C{sub 6}H{sub 5}{sup 13}CH{sub 2}) suggests the Benson fragmentation and the norbornadienyl pathways open at reactor temperatures of 1300 K while the methyl-phenyl radical channel becomes active at slightly higher temperatures (1500 K).« less
  • Cited by 4
  • Cycloheptatrienyl (tropyl) radical, C7H7, was cleanly produced in the gas-phase, entrained in He or Ne carrier gas, and subjected to a set of flash-pyrolysis micro-reactors. The pyrolysis products resulting from C7H7 were detected and identified by vacuum ultraviolet photoionization mass spectrometry. Complementary product identification was provided by infrared absorption spectroscopy. Pyrolysis pressures in the micro-reactor were roughly 200 Torr and residence times were approximately 100 us. Thermal cracking of tropyl radical begins at 1100 K and the products from pyrolysis of C7H7 are only acetylene and cyclopentadienyl radicals. Tropyl radicals do not isomerize to benzyl radicals at reactor temperatures upmore » to 1600 K. Heating samples of either cycloheptatriene or norbornadiene never produced tropyl (C7H7) radicals but rather only benzyl (C6H5CH2). The thermal decomposition of benzyl radicals has been reconsidered without participation of tropyl radicals. There are at least three distinct pathways for pyrolysis of benzyl radical: the Benson fragmentation, the methyl-phenyl radical, and the bridgehead norbornadienyl radical. These three pathways account for the majority of the products detected following pyrolysis of all of the isotopomers: C6H5CH2, C6H5CD2, C6D5CH2, and C6H5 13CH2. Analysis of the temperature dependence for the pyrolysis of the isotopic species (C6H5CD2, C6D5CH2, and C6H5 13CH2) suggests the Benson fragmentation and the norbornadienyl pathways open at reactor temperatures of 1300 K while the methyl-phenyl radical channel becomes active at slightly higher temperatures (1500 K).« less
  • Cycloheptatrienyl (tropyl) radical, C 7H 7, was cleanly produced in the gas-phase, entrained in He or Ne carrier gas, and subjected to a set of flash-pyrolysis micro-reactors. In this study, the pyrolysis products resulting from C 7H 7 were detected and identified by vacuum ultraviolet photoionization mass spectrometry. Complementary product identification was provided by infrared absorption spectroscopy. Pyrolysis pressures in the micro-reactor were roughly 200 Torr and residence times were approximately 100 μs. Thermal cracking of tropyl radical begins at 1100 K and the products from pyrolysis of C 7H 7 are only acetylene and cyclopentadienyl radicals. Tropyl radicals domore » not isomerize to benzyl radicals at reactor temperatures up to 1600 K. Heating samples of either cycloheptatriene or norbornadiene never produced tropyl (C 7H 7) radicals but rather only benzyl (C 6H 5CH 2). The thermal decomposition of benzyl radicals has been reconsidered without participation of tropyl radicals. There are at least three distinct pathways for pyrolysis of benzyl radical: the Benson fragmentation, the methyl-phenyl radical, and the bridgehead norbornadienyl radical. These three pathways account for the majority of the products detected following pyrolysis of all of the isotopomers: C 6H 5CH 2, C 6H 5CD 2, C 6D 5CH 2, and C 6H 5 13CH 2. Finally, analysis of the temperature dependence for the pyrolysis of the isotopic species (C 6H 5CD 2, C 6D 5CH 2, and C 6H 5 13CH 2) suggests the Benson fragmentation and the norbornadienyl pathways open at reactor temperatures of 1300 K while the methyl-phenyl radical channel becomes active at slightly higher temperatures (1500 K).« less