Observation and Assignment of Silent and Higher Order Vibrations in the Infrared Transmission of C60 Crystals

TL;DR

This study comprehensively measures and analyzes the infrared vibrational spectra of C60 crystals, revealing numerous silent and higher order modes, and correlates these with Raman and neutron scattering data to identify 46 key vibrational modes.

Contribution

It provides a detailed assignment of vibrational modes in C60, including silent and higher order modes, using combined IR, Raman, and neutron scattering data, with a complete fit of observed spectra.

Findings

Over 180 vibrational absorptions observed in C60 IR spectra

Identification of silent modes becoming IR-active

Complete fit of IR and Raman data using 46 vibrational modes

Abstract

We report the measurement of infrared transmission of large C60 single crystals. The spectra exhibit a very rich structure with over 180 vibrational absorptions visible in the 100 - 4000 cm-1 range. Many silent modes are observed to have become weakly IR-active. We also observe a large number of higher order combination modes. The temperature (77K - 300K) and pressure (0 - 25KBar) dependencies of these modes were measured and are presented. Careful analysis of the IR spectra in conjunction with Raman scattering data showing second order modes and neutron scattering data, allow the selection of the 46 vibrational modes C60. We are able to fit *all* of the first and second order data seen in the present IR spectra and the previously published Raman data (~300 lines total), using these 46 modes and their group theory allowed second order combinations.