Multichannel Quantum Defect Theory for cold molecular collisions with a strongly anisotropic potential energy surface

TL;DR

This paper demonstrates an improved multichannel quantum defect theory (MQDT) approach for efficiently calculating cold molecular collision cross sections in Li+NH systems with strongly anisotropic potentials, aiding sympathetic cooling studies.

Contribution

An improved MQDT method that removes closed-channel poles, enabling efficient and accurate calculations of cold molecular collisions with strongly anisotropic potentials.

Findings

Successfully applied MQDT to Li+NH collisions.

Reduced computational effort by using only 5 energy-field combinations.

Provided cross sections relevant for sympathetic cooling feasibility.

Abstract

We show that multichannel quantum defect theory (MQDT) can be applied successfully as an efficient computational method for cold molecular collisions in Li+NH, which has a deep and strongly anisotropic interaction potential. In this strongly coupled system, closed-channel poles restrict the range over which the MQDT Y matrix can be interpolated. We present an improved procedure to transform the MQDT reference functions so that the poles are removed from the energy range of interest. Effects due to very long-range spin-dipolar couplings are outside the scope of MQDT, but can be added perturbatively. The new procedure makes it possible to calculate the elastic and inelastic cross sections needed to evaluate the feasibility of sympathetic cooling of NH by Li using coupled-channel calculations at only 5 combinations of energy and field.