# Dicarbon formation in collisions of two carbon atoms

## TL;DR

This paper calculates quantum mechanical radiative association rates for C$_2$ molecule formation during C atom collisions, providing new molecular data and comparing results with semi-classical methods for astrophysical and laboratory applications.

## Contribution

It introduces new ab initio potential curves and transition dipole moments for dicarbon, enhancing molecular data and improving accuracy of formation rate calculations.

## Key findings

- Main contributions from specific electronic states identified.
- Quantum approach yields different rates compared to semi-classical methods.
- Results applicable to astrophysical and laboratory environments.

## Abstract

Radiative association cross sections and rates are computed, using a quantum approach, for the formation of C$_2$ molecules (dicarbon) during the collision of two ground state C($^3$P) atoms. We find that transitions originating in the C$\;^1\Pi_g$, d$\;^3\Pi_g$, and 1$\;^5\Pi_u$ states are the main contributors to the process. The results are compared and contrasted with previous results obtained from a semi-classical approximation. New ab initio potential curves and transition dipole moment functions have been obtained for the present work using the multi-reference configuration interaction approach with the Davidson correction (MRCI+Q) and aug-cc-pCV5Z basis sets, substantially increasing the available molecular data on dicarbon. Applications of the current computations to various astrophysical environments and laboratory studies are briefly discussed focusing on these rates.