Cold heteromolecular dipolar collisions

TL;DR

This paper reports the first experimental observation of cold heteromolecular dipolar collisions between two different neutral polar molecules, using advanced cooling and trapping techniques to measure collision cross sections at low energies.

Contribution

It introduces a novel experimental setup combining Stark deceleration, magnetic trapping, and cryogenic cooling to study cold molecular collisions, and provides the first theoretical analysis of such collisions involving a radical and a polyatomic molecule.

Findings

Measured total trap loss cross sections at 5 K.

Cross sections increase with external electric field due to dipolar interactions.

Theoretical calculations agree with experimental measurements at zero field.

Abstract

We present the first experimental observation of cold collisions between two different species of neutral polar molecules, each prepared in a single internal quantum state. Combining for the first time the techniques of Stark deceleration, magnetic trapping, and cryogenic buffer gas cooling allows the enhancement of molecular interaction time by 10$^5$. This has enabled an absolute measurement of the total trap loss cross sections between OH and ND$_3$ at a mean collision energy of 3.6 cm$^{-1}$ (5 K). Due to the dipolar interaction, the total cross section increases upon application of an external polarizing electric field. Cross sections computed from \emph{ab initio} potential energy surfaces are in excellent agreement with the measured value at zero external electric field. The theory presented here represents the first such analysis of collisions between a $^2\Pi$ radical and a closed-shell polyatomic molecule.