Letter to the Editor

Mapping the structural diversity of C₆₀ carbon clusters and their infrared spectra

¹ Laboratoire de Chimie et Physique Quantiques LCPQ/IRSAMC, Université de Toulouse and CNRS, UT3-Paul Sabatier, 118 Route de Narbonne, 31062 Toulouse, France
e-mail: aude.simon@irsamc.ups-tlse.fr
² Institut des Sciences Moléculaires d’Orsay (ISMO), CNRS, Univ. Paris Sud, Université Paris-Saclay, 91405 Orsay, France
³ Univ. Grenoble Alpes, CNRS, LIPhy, 38000 Grenoble, France

Received: 21 December 2018
Accepted: 1 May 2019

Abstract

The current debate about the nature of the carbonaceous material carrying the infrared (IR) emission spectra of planetary and proto-planetary nebulae, including the broad plateaus, calls for further studies on the interplay between structure and spectroscopy of carbon-based compounds of astrophysical interest. The recent observation of C₆₀ buckminsterfullerene in space suggests that carbon clusters of similar size may also be relevant. In the present work, broad statistical samples of C₆₀ isomers were computationally determined without any bias using a reactive force field, their IR spectra being subsequently obtained following local optimization with the density-functional-based tight-binding theory. Structural analysis reveals four main structural families identified as cages, planar polycyclic aromatics, pretzels, and branched. Comparison with available astronomical spectra indicates that only the cage family could contribute to the plateau observed in the 6–9 μm region. The present framework shows great promise to explore and relate structural and spectroscopic features in more diverse and possibly hydrogenated carbonaceous compounds, in relation with astronomical observations.