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S 0 and S 1 spectroscopy of jet cooled 9-cyano-10-methylanthracene: The methyl group as a molecular rotor

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Title: S 0 and S 1 spectroscopy of jet cooled 9-cyano-10-methylanthracene: The methyl group as a molecular rotor
Authors: Mordziński, A.1, Leś, A.2, Stepanenko, Y.1 stepanenko@ichf.edu.pl, Rycombel, J.2, Adamowicz, L.3
Source: Journal of Molecular Spectroscopy. Sep2005, Vol. 233 Issue 1, p98-109. 12p.
Subjects: Fluorescence, Methyl groups, Spectrum analysis, Phase shift (Nuclear physics), Radioactivity
Abstract: Abstract: Jet-cooled fluorescence excitation and dispersed fluorescence spectra of 9-methylanthracene (MA), 9-cyanoanthracene (CA) and 9-cyano-10-methylanthracene (CMA) have been measured. The spectra of MA and CMA near the S 0–S 1 origin reveal a prominent torsional progression due to the hindered methyl group rotation and its torsional vibration against the aromatic ring frame. Additionally, the laser induced fluorescence LIF excitation spectrum of CMA shows the splitting of many vibrational modes. Observed positions and relative intensities of the methyl internal rotational bands were interpreted in terms of transitions calculated based on the quantum mechanical one-dimensional rotor. The low-frequency vibrational bands were interpreted also with the all electron quantum mechanical calculations within the RHF/6-31G(d,p), CIS/3-21G and CIS/6-31G(d,p) approximations. It is predicted that in the case of MA the eclipsed geometry (one C–H in the plane of the ring) is most stable in both S 0 and S 1 states. Conformation of the methyl group in CMA is suggested to change upon S 1 ← S 0 excitation (π/12 phase shift of the methyl group). The predicted energy barrier for methyl group rotation in the S 0 state of CMA is considerably higher (72cm−1) than that in the S 1 state (22cm−1). Following the present quantum mechanical calculations, the carbon atom of the methyl group belongs to the aromatic plane in the S 0 ground state but it deviates from this plane in the S 1 excited state. These in turn suggest that the calculated barrier for methyl group rotation in CMA has a 6-fold symmetry in the S 0 ground state and roughly a 4-fold symmetry in the S 1 state. [Copyright &y& Elsevier]
Copyright of Journal of Molecular Spectroscopy is the property of Academic Press Inc. and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
Database: Engineering Source
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Header DbId: egs
DbLabel: Engineering Source
An: 18195972
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PubTypeId: academicJournal
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  Data: S <subscript>0</subscript> and S <subscript>1</subscript> spectroscopy of jet cooled 9-cyano-10-methylanthracene: The methyl group as a molecular rotor
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  Data: <searchLink fieldCode="AR" term="%22Mordziński%2C+A%2E%22">Mordziński, A.</searchLink><relatesTo>1</relatesTo><br /><searchLink fieldCode="AR" term="%22Leś%2C+A%2E%22">Leś, A.</searchLink><relatesTo>2</relatesTo><br /><searchLink fieldCode="AR" term="%22Stepanenko%2C+Y%2E%22">Stepanenko, Y.</searchLink><relatesTo>1</relatesTo><i> stepanenko@ichf.edu.pl</i><br /><searchLink fieldCode="AR" term="%22Rycombel%2C+J%2E%22">Rycombel, J.</searchLink><relatesTo>2</relatesTo><br /><searchLink fieldCode="AR" term="%22Adamowicz%2C+L%2E%22">Adamowicz, L.</searchLink><relatesTo>3</relatesTo>
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  Data: <searchLink fieldCode="JN" term="%22Journal+of+Molecular+Spectroscopy%22">Journal of Molecular Spectroscopy</searchLink>. Sep2005, Vol. 233 Issue 1, p98-109. 12p.
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  Data: <searchLink fieldCode="DE" term="%22Fluorescence%22">Fluorescence</searchLink><br /><searchLink fieldCode="DE" term="%22Methyl+groups%22">Methyl groups</searchLink><br /><searchLink fieldCode="DE" term="%22Spectrum+analysis%22">Spectrum analysis</searchLink><br /><searchLink fieldCode="DE" term="%22Phase+shift+%28Nuclear+physics%29%22">Phase shift (Nuclear physics)</searchLink><br /><searchLink fieldCode="DE" term="%22Radioactivity%22">Radioactivity</searchLink>
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  Label: Abstract
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  Data: Abstract: Jet-cooled fluorescence excitation and dispersed fluorescence spectra of 9-methylanthracene (MA), 9-cyanoanthracene (CA) and 9-cyano-10-methylanthracene (CMA) have been measured. The spectra of MA and CMA near the S 0–S 1 origin reveal a prominent torsional progression due to the hindered methyl group rotation and its torsional vibration against the aromatic ring frame. Additionally, the laser induced fluorescence LIF excitation spectrum of CMA shows the splitting of many vibrational modes. Observed positions and relative intensities of the methyl internal rotational bands were interpreted in terms of transitions calculated based on the quantum mechanical one-dimensional rotor. The low-frequency vibrational bands were interpreted also with the all electron quantum mechanical calculations within the RHF/6-31G(d,p), CIS/3-21G and CIS/6-31G(d,p) approximations. It is predicted that in the case of MA the eclipsed geometry (one C–H in the plane of the ring) is most stable in both S 0 and S 1 states. Conformation of the methyl group in CMA is suggested to change upon S 1 ← S 0 excitation (π/12 phase shift of the methyl group). The predicted energy barrier for methyl group rotation in the S 0 state of CMA is considerably higher (72cm−1) than that in the S 1 state (22cm−1). Following the present quantum mechanical calculations, the carbon atom of the methyl group belongs to the aromatic plane in the S 0 ground state but it deviates from this plane in the S 1 excited state. These in turn suggest that the calculated barrier for methyl group rotation in CMA has a 6-fold symmetry in the S 0 ground state and roughly a 4-fold symmetry in the S 1 state. [Copyright &y& Elsevier]
– Name: AbstractSuppliedCopyright
  Label:
  Group: Ab
  Data: <i>Copyright of Journal of Molecular Spectroscopy is the property of Academic Press Inc. and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.)
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        Value: 10.1016/j.jms.2005.06.007
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      – SubjectFull: Spectrum analysis
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      – SubjectFull: Phase shift (Nuclear physics)
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      – SubjectFull: Radioactivity
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      – TitleFull: S 0 and S 1 spectroscopy of jet cooled 9-cyano-10-methylanthracene: The methyl group as a molecular rotor
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              Text: Sep2005
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