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Internet Electronic Journal of Molecular Design - IEJMD, ISSN 1538-6414, CODEN IEJMAT
| ABSTRACT - Internet Electron. J. Mol. Des. September 2003, Volume 2, Number 9, 578-588 |
Ab initio MR-CI Investigation of Linear HC5H+
and HC7H+
Max Muhlhauser, Jan Haubrich, Giannis Mpourmpakis, Andreas Mavrandonakis, and George E. Froudakis
Internet Electron. J. Mol. Des. 2003, 2, 578-588
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Abstract:
Linear hydrocarbon clusters with a large ratio of carbon to
hydrogen are expected to be widely distributed in the
interstellar environments. Positively charged clusters are very
reactive and provide difficulties for experimental
investigation. On the other hand it is known that theoretical
studies of excited states can predict approximate transition
energies and oscillator strengths so that such computations
are an almost ideal tool to help the experimental search.
Multi-reference configuration interaction (MR-CI)
calculations are employed to compute the vertical electronic
spectra of HC5H+ and HC7H+. The lowest dipole-allowed
transitions are computed at 2.56 eV (HC5H+) and 2.34 eV
(HC7H+) in reasonable agreement with experimental work of
499 nm (2.47 eV, HC5H+) and 600 nm (2.06 eV, HC7H+).
Further transitions with relatively large oscillator strength are
predicted at 3.85 eV (32Πg) and 7.03 eV
(42Πg) for HC5H+
and at 3.17 eV (32Πu) and 6.01 eV
(42Πu) for HC7H+. In both
molecules the energy difference between SOMO and LUMO
is similar to the energy difference between HOMO and
SOMO. The description of the two corresponding states
shows multi-reference character. The lowering of these
transition energies on increase of chain-length is in line with
a smaller HOMO-SOMO and SOMO-LUMO gap.
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