Dramatic Reduction of IR Vibrational Cross Sections of Molecules Encapsulated in Carbon Nanotubes

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• 作者：Dmitry V. Kazachkin ; Yoshifumi Nishimura ; Henryk A. Witek ; Stephan Irle ; Eric Borguet
• 刊名：Journal of the American Chemical Society
• 出版年：2011
• 出版时间：June 1, 2011
• 年：2011
• 卷：133
• 期：21
• 页码：8191-8198
• 全文大小：975K
• 年卷期：v.133,no.21(June 1, 2011)
• ISSN：1520-5126

文摘

Combined temperature-programmed desorption and IR studies suggest that absorption cross sections of IR-active vibrations of molecules 鈥渟trongly鈥?bound to single-wall carbon nanotubes (SWCNTs) are reduced at least by a factor of 10. Quantum chemical simulations show that IR intensities of endohedrally encapsulated molecules are dramatically reduced, and identify dielectric screening by highly polarizable SWCNT sidewalls as the origin of such 鈥渟creening鈥? The observed intensity reduction originates from a sizable cancellation of adsorbate dipole moments by mirror charges dynamically induced on the nanotube sidewalls. For exohedrally adsorbed molecules, the dielectric screening is found to be orientation-dependent with a smaller magnitude for adsorption in groove and interstitial sites. The presented results clearly demonstrate and quantify the screening effect of SWCNTs and unequivocally show that IR spectroscopy cannot be applied in a straightforward manner to the study of peapod systems.