Quantum Defect Theory for Cold Chemistry with Product Quantum State Resolution

TL;DR

This paper introduces a hybrid quantum defect theory and close-coupling method for cold atom-diatom reactions, enabling detailed state-to-state cross sections with reduced computational cost.

Contribution

It develops a novel hybrid formalism combining quantum defect theory with close-coupling calculations for efficient, rovibrationally resolved reaction analysis.

Findings

Accurate for a wide range of collision energies

Reduces computational expense compared to full close-coupling calculations

Successfully applied to D+H₂ reaction with product state resolution

Abstract

We present a formalism for cold and ultracold atom-diatom chemical reactions that combines a quantum close-coupling method at short-range with quantum defect theory at long-range. The method yields full state-to-state rovibrationally resolved cross sections as in standard close-coupling (CC) calculations but at a considerably less computational expense. This hybrid approach exploits the simplicity of MQDT while treating the short-range interaction explicitly using quantum CC calculations. The method, demonstrated for D+H$_2\to$ HD+H collisions with rovibrational quantum state resolution of the HD product, is shown to be accurate for a wide range of collision energies and initial conditions. The hybrid CC-MQDT formalism may provide an alternative approach to full CC calculations for cold and ultracold reactions.