# C20 and nitrogen-substituted fullerenes: anharmonic IR and UV-vis spectra for astrophysical environments

## TL;DR

This paper studies the IR and UV-vis spectra of C20 fullerenes and nitrogen-substituted variants to understand their presence in astrophysical environments.

## Contribution

The study introduces new theoretical insights into the spectral features of nitrogen-substituted C20 fullerenes in astrophysical contexts.

## Key findings

- Nitrogen substitution in C20 creates stable heterofullerenes with distinct IR peaks matching observed astronomical features.
- Electronic absorption spectra align with the ultraviolet bump at 217 nm in the interstellar extinction curve.
- Spectral peaks at 6.2, 6.67, 7.0, 7.7, 8.5, 11.3, and 12.8 μm match observations in planetary and reflection nebulae.

## Abstract

Theoretical infrared (IR) and electronic absorption spectra of the C20 fullerene and its nitrogen-substituted heterofullerenes in gas and water solvent are studied and discussed in terms of astronomical observations. The replacement of a carbon atom by nitrogen results in two stable heterofullerenes, which is confirmed by their HOMO to LUMO energy gap. The ionization potential and electron affinity of these molecules are reported. Theoretical calculations performed at the B3LYP/6-311++G(d,p) level of density functional theory (DFT). The effect of water solvent is studied using the integral equation formalism polarized continuum model (IEFPCM) at the same level of theory. Effects of substitution on the electronic and absorption spectra of these molecules are studied. The results of the C20 fullerene and its heterofullerenes show spectra with peaks at 6.2, 6.67, 7.0, 7.7, 8.5, 11.3, and 12.8 μm, which have corresponding features in observed spectra of the planetary nebulae Tc1 and NGC 7027, and the reflection nebulae NGC 2023 and NGC 7023. The electronic absorption spectra of these molecules are also calculated by time-dependent DFT (TD-DFT) and discussed in relation to the ultraviolet bump feature at 217 nm in the interstellar extinction curve. We estimate the transition wavelength, oscillator strength, and symmetry using the AOMix program.

Theoretical infrared (IR) and electronic absorption spectra of the C20 fullerene and its nitrogen-substituted heterofullerenes in gas and water solvent are studied and discussed in terms of astronomical observations.