The vertical and adiabatic ionization energies of silicon carbide clusters, (SiC)$_n$, with n=1-12

TL;DR

This study investigates the ionization energies and structures of small silicon carbide clusters, providing insights into their stability and formation, which are crucial for understanding cosmic dust nucleation in space environments.

Contribution

The paper presents the first detailed calculations of ionization energies and structures of (SiC)$_n$ clusters for n=2-12, revealing size-dependent stability and structural differences from neutral to ionized forms.

Findings

Ionization energies range from 6.6 to 10.0 eV, lower than the SiC molecule.

Neutral and singly ionized clusters have similar structures for n=5-12.

Small clusters (n=2-4) show metastable and different cation geometries.

Abstract

Silicon carbide (SiC) is one of the major cosmic dust components in carbon-rich environments. However, the formation of SiC dust is not well understood. In particular, the initial stages of the SiC condensation (i.e. the SiC nucleation) remain unclear, as the basic building blocks (i.e. molecular clusters) exhibit atomic segregation at the (sub-)nanoscale. We report vertical and adiabatic ionization energies of small silicon carbide clusters, (SiC)$_n$ , n=2-12, ranging from 6.6-10.0 eV, which are lower than for the SiC molecule ($\sim$ 10.6 eV). The most favorable structures of the singly ionized (SiC)$_n^+$, n=5-12, cations resemble their neutral counterparts. However, for sizes n=2-4, these structural analogues are metastable and different cation geometries are favored. Moreover, we find that the (SiC)$_5^+$ cation is likely to be a transition state. Therefore, we place constraints on the stability limit for small, neutral (SiC)$_n$ clusters to persist ionization through (inter)-stellar radiation fields or high temperatures.