Chemistry in a Cryogenic Buffer Gas Cell

TL;DR

This paper investigates chemical reactions between calcium and hydrogen isotopologues in a cryogenic buffer gas cell, revealing how vibrational excitations enhance molecular yields for cold molecular beam production.

Contribution

It introduces a reaction network model explaining chemical dynamics in cryogenic cells and demonstrates how H$_2$ enhances molecular yields through vibrational excitations.

Findings

H$_2$ outperforms D$_2$ and HD as a reactant and buffer gas.

Vibrational excitations of H$_2$ increase molecular yield.

Method enables production of bright cold beams of alkaline-earth-metal hydrides.

Abstract

Cryogenic buffer gas sources are ubiquitous for producing cold, collimated molecular beams for quantum science, chemistry, and precision measurements. The molecules are typically produced by laser ablating a metal target in the presence of a donor gas. The radical of interest emerges due to a barrier-free reaction or under thermal or optical excitation. High-barrier reactions, such as between Ca and H$_2$, should be precluded. We study chemical reactions between Ca and three hydrogen isotopologues H$_2$, D$_2$, and HD in a cryogenic cell with helium buffer gas. We observe that H$_2$ can serve as both a reactant and a buffer gas, outperforming D$_2$ and HD. We use a reaction network model to describe the chemical dynamics and find that the enhanced molecular yield can be attributed to rapid vibrational excitations of the reactant gas. Our results demonstrate a robust method for generating bright cold beams of alkaline-earth-metal hydrides for laser cooling and trapping.