The electronic states of 1,2,4-triazoles: A study of 1H- and 1-methyl-1,2,4-triazole by vacuum ultraviolet photoabsorption and ultraviolet photoelectron spectroscopy and a comparison with ab initio configuration interaction computations

Michael H. Palmer, Philip J. Camp, Sren Vrnning Hoffmann, Nykola C. Jones, Ashley R. Head, Dennis L Lichtenberger

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Abstract

The first vacuum ultraviolet absorption spectrum of a 1,2,4-triazole has been obtained and analyzed in detail, with assistance from both an enhanced UV photoelectron spectroscopic study and ab initio multi-reference multi-root configuration interaction procedures. For both 1H- and 1-methyl-1,2,4-triazoles, the first ionization energy bands show complex vibrational structure on the low-energy edges of otherwise unstructured bands. Detailed analysis of these bands confirms the presence of three ionized states. The 6-7 eV VUV spectral region shows an unusual absorption plateau, which is interpreted in terms of the near degeneracy of the first two ionization energies, leading to a pseudo Jahn-Teller effect. The fingerprint of the ionization spectrum yields band origins for several Rydberg states. The configuration interaction study shows that although the equilibrium structure for the first cation is effectively planar, the second cation shows significant twisting of the ring system. Some calculated singlet electronic states also show skeletal twisting in which the ring C-H is substantially out of plane.

Original languageEnglish (US)
Article number094310
JournalThe Journal of Chemical Physics
Volume136
Issue number9
DOIs
StatePublished - Mar 7 2012

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Ultraviolet photoelectron spectroscopy
Ionization potential
ultraviolet spectroscopy
Electronic states
photoabsorption
configuration interaction
Cations
Rydberg states
photoelectron spectroscopy
twisting
Vacuum
Jahn-Teller effect
ionization
vacuum
Photoelectrons
electronics
Band structure
Ionization
cations
Absorption spectra

ASJC Scopus subject areas

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry

Cite this

@article{946635c3ce594b019a0c475358878447,
title = "The electronic states of 1,2,4-triazoles: A study of 1H- and 1-methyl-1,2,4-triazole by vacuum ultraviolet photoabsorption and ultraviolet photoelectron spectroscopy and a comparison with ab initio configuration interaction computations",
abstract = "The first vacuum ultraviolet absorption spectrum of a 1,2,4-triazole has been obtained and analyzed in detail, with assistance from both an enhanced UV photoelectron spectroscopic study and ab initio multi-reference multi-root configuration interaction procedures. For both 1H- and 1-methyl-1,2,4-triazoles, the first ionization energy bands show complex vibrational structure on the low-energy edges of otherwise unstructured bands. Detailed analysis of these bands confirms the presence of three ionized states. The 6-7 eV VUV spectral region shows an unusual absorption plateau, which is interpreted in terms of the near degeneracy of the first two ionization energies, leading to a pseudo Jahn-Teller effect. The fingerprint of the ionization spectrum yields band origins for several Rydberg states. The configuration interaction study shows that although the equilibrium structure for the first cation is effectively planar, the second cation shows significant twisting of the ring system. Some calculated singlet electronic states also show skeletal twisting in which the ring C-H is substantially out of plane.",
author = "Palmer, {Michael H.} and Camp, {Philip J.} and Hoffmann, {Sren Vrnning} and Jones, {Nykola C.} and Head, {Ashley R.} and Lichtenberger, {Dennis L}",
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AU - Palmer, Michael H.

AU - Camp, Philip J.

AU - Hoffmann, Sren Vrnning

AU - Jones, Nykola C.

AU - Head, Ashley R.

AU - Lichtenberger, Dennis L

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N2 - The first vacuum ultraviolet absorption spectrum of a 1,2,4-triazole has been obtained and analyzed in detail, with assistance from both an enhanced UV photoelectron spectroscopic study and ab initio multi-reference multi-root configuration interaction procedures. For both 1H- and 1-methyl-1,2,4-triazoles, the first ionization energy bands show complex vibrational structure on the low-energy edges of otherwise unstructured bands. Detailed analysis of these bands confirms the presence of three ionized states. The 6-7 eV VUV spectral region shows an unusual absorption plateau, which is interpreted in terms of the near degeneracy of the first two ionization energies, leading to a pseudo Jahn-Teller effect. The fingerprint of the ionization spectrum yields band origins for several Rydberg states. The configuration interaction study shows that although the equilibrium structure for the first cation is effectively planar, the second cation shows significant twisting of the ring system. Some calculated singlet electronic states also show skeletal twisting in which the ring C-H is substantially out of plane.

AB - The first vacuum ultraviolet absorption spectrum of a 1,2,4-triazole has been obtained and analyzed in detail, with assistance from both an enhanced UV photoelectron spectroscopic study and ab initio multi-reference multi-root configuration interaction procedures. For both 1H- and 1-methyl-1,2,4-triazoles, the first ionization energy bands show complex vibrational structure on the low-energy edges of otherwise unstructured bands. Detailed analysis of these bands confirms the presence of three ionized states. The 6-7 eV VUV spectral region shows an unusual absorption plateau, which is interpreted in terms of the near degeneracy of the first two ionization energies, leading to a pseudo Jahn-Teller effect. The fingerprint of the ionization spectrum yields band origins for several Rydberg states. The configuration interaction study shows that although the equilibrium structure for the first cation is effectively planar, the second cation shows significant twisting of the ring system. Some calculated singlet electronic states also show skeletal twisting in which the ring C-H is substantially out of plane.

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