Are fulleranes responsible for the 21 micron feature?

TL;DR

This study explores whether fulleranes, hydrogenated fullerenes, could be responsible for the mysterious 21-micron infrared feature observed in some protoplanetary nebulae, using theoretical vibrational spectra analysis.

Contribution

It provides a theoretical investigation into fulleranes as potential carriers of the 21-micron feature, including analysis of vibrational spectra and initial hydrogen coverage estimates.

Findings

Evidence both supports and challenges the fullerane hypothesis.

Theoretical vibrational spectra suggest possible contributions of fulleranes to the 21-micron feature.

Initial hydrogen coverage estimates offer insights into fullerane emission characteristics.

Abstract

Recent detections of C$_{60}$, C$_{70}$, and C$_{60}^+$ in space induced extensive studies of fullerene derivatives in circumstellar environments. As the promising fullerene sources, protoplanetary nebulae (PPNe) show a number of unidentified bands in their infrared spectra, among which a small sample exhibits an enigmatic feature at $\sim21$\,$\mu$m. Hydrogenation of fullerenes can produce fulleranes emitting new infrared bands. In this paper, we investigate the possibility of fulleranes (C$_{60}$H$_m$) as the carrier of the 21\,$\mu$m feature in terms of theoretical vibrational spectra of fulleranes. The evidences favoring and disfavoring the fullerane hypothesis are presented. We made an initial guess for the hydrogen coverage of C$_{60}$H$_m$ that may contribute to the 21\,$\mu$m feature.