Formation of silicon monoxide by radiative association: the impact of resonances

TL;DR

This study uses advanced quantum chemistry to calculate SiO formation rates via radiative association, revealing that resonances significantly enhance low-temperature reaction rates, impacting astrophysical models.

Contribution

It provides high-accuracy molecular data and demonstrates the crucial role of resonances in radiative association rate calculations for SiO.

Findings

Resonances increase rate coefficients at low temperatures by several orders of magnitude.

Quantum calculations differ markedly from semiclassical results.

New formation rates have potential implications for astrophysical environments.

Abstract

Detailed quantum chemistry calculations within the multireference configuration interaction approximation with the Davidson correction (MRCI+Q) are presented using an aug-cc-pV6Z basis set, for the potential energy curves and transition dipole moments between low lying molecular states of singlet spin symmetry for the SiO molecule. The high quality molecular data are used to obtain radiative association cross sections and rate coefficients for collisions between ground state Si and O atoms. Quantal calculations are compared with semiclassical results. Using a quantum kinetic theory of radiative association in which quasibound levels are assumed to be in local thermodynamic equilibrium, we find that resonances play an important role in enhancing the rate coefficients at low temperatures by several orders of magnitude from that predicted by standard quantum scattering formulations. These new molecular formation rates may have important implications for applications in astrophysics.