Radiative Association of Ag and H: Formation of AgH from Ab Initio Calculations

TL;DR

This study uses quantum scattering theory and ab initio calculations to analyze the radiative association of silver and hydrogen, providing new kinetic data crucial for astrochemical models of metal hydride formation in space.

Contribution

First quantum scattering analysis of AgH formation with detailed potential energy surfaces and transition dipole moments from ab initio methods.

Findings

Identification of shape resonances affecting low-energy collision outcomes

Modest enhancement of formation rates under blackbody radiation at high temperatures

Decreasing thermal rate coefficients with increasing temperature

Abstract

Radiative association processes leading to the formation of AgH in cold astrophysical environments are investigated for the first time using full quantum scattering theory. High accuracy potential energy curves and transition dipole moments for the low-lying electronic states (X$^1\Sigma^+$, A$^1\Sigma^+$, $1^1\Pi$, $3^1\Sigma^+$, $2^1\Pi$) are computed employing the internally contracted multireference configuration interaction method with Davidson correction. Vibrationally and rotationally resolved radiative association cross sections are calculated for transitions from these initial states to the ground X$^1\Sigma^+$ state. Prominent shape resonances arising from quasi-bound rovibrational levels behind centrifugal barriers are identified, with the $2^1\Pi \to$ X$^1\Sigma^+$ channel exhibiting the strongest contribution at low collision energies. Stimulated radiative association under blackbody radiation fields (up to $T = 20\,000$ K) produces modest enhancements, predominantly in the ground-state channel. Thermal rate coefficients computed over 10$^{-1}$--$10^4$~K reveal a general decreasing trend with temperature for all channels. The results provide essential kinetic data for astrochemical models of transition-metal hydride formation in low-temperature interstellar and circumstellar environments.