# Universal rate constants for reactive collisions of ultracold molecules

## TL;DR

This paper introduces a quantum defect model that provides universal expressions for collision rates of ultracold molecules, explaining experimental results and predicting rate constants independent of short-range dynamics.

## Contribution

The paper presents an analytic quantum defect model that predicts universal collision rate constants for ultracold molecules, applicable when reaction probabilities are high.

## Key findings

- Model accurately predicts measured rate constants for ultracold 40K87Rb molecules.
- Provides analytic expressions for s- and p-wave collision rates.
- Explains the universality of certain ultracold molecular collision rates.

## Abstract

A simple quantum defect model gives analytic expressions for the complex scattering length and threshold collision rates of ultracold molecules. If the probability of reaction in the short-range part of the collision is high, the model gives universal rate constants for s- and p-wave collisions that are independent of short-range dynamics. This model explains the magnitudes of the recently measured rate constants for collisions of two ultracold 40K87Rb molecules, or an ultracold 40K atom with the 40K87Rb molecule [Ospelkaus et al., Science 327, 853 (2010)].