Can Raman spectroscopy detect cumulenic structures of linear carbon chains?
Article first published online: 8 SEP 2009
Copyright © 2009 John Wiley & Sons, Ltd.
Journal of Raman Spectroscopy
Volume 41, Issue 2, pages 226–236, February 2010
How to Cite
Innocenti, F., Milani, A. and Castiglioni, C. (2010), Can Raman spectroscopy detect cumulenic structures of linear carbon chains?. J. Raman Spectrosc., 41: 226–236. doi: 10.1002/jrs.2413
- Issue published online: 15 FEB 2010
- Article first published online: 8 SEP 2009
- Manuscript Accepted: 4 JUL 2009
- Manuscript Received: 21 MAY 2009
- Italian Ministry of Education
- linear carbon chains;
- first principles calculations;
- Raman intensity;
- bond length alternation;
- phonon dispersion curves
The molecular and vibrational structures of cumulenic carbon chains are investigated by density functional theory calculations and compared with that of hydrogen-capped polyynes. The small value of bond length alternation (BLA) along the CC bonds sequence obtained by geometry optimization of uncapped Cn chains and vinyl-capped carbon chains confirms their cumulenic structure. It is demonstrated that for finite length chains the structural parameters are determined by end effects as far as the Peierls distortion, expected for very long molecules, does not occur. The Raman spectra of such molecules are calculated to verify the possibility of identifying markers of cumulenic chains by means of vibrational spectroscopy. As expected, the longitudinal mode consisting of the BLA oscillation, which is responsible for the strongest Raman transition of polyynes, becomes very weak for cumulenes; this behaviour is rationalized in terms of local polarizability derivatives. However, other longitudinal modes can be observed in the Raman spectra of Cn chains. The wavenumber behaviour and the optical activity of these modes are interpreted on the basis of the phonon dispersion branch of an ideally infinite cumulenic polymer. Raman intensities computed for chains of different lengths allow to conclude that cumulenic molecules could be detected and identified by means of Raman spectroscopy. Copyright © 2009 John Wiley & Sons, Ltd.