Chemistry with hydrogen gas in a cryogenic buffer gas cell

Chemical reactions in the cold, diffuse regime present practical interest - such as in astrophysical environments or as sources for cold molecular beams. These reactions are also theoretically interesting due to the quasi-classical nature of the collisions. Cryogenic buffer gas cells are an excellent platform to study chemistry in this regime. Here, we present the reaction of Ca with three hydrogen isotopologues - H₂, D₂, and HD - to produce CaH or CaD molecules in a buffer gas cell at 6 K. We show that H₂ produces a far brighter beam than the other isotopologues, and serves as both a reactant and a buffer gas. To model the reactions we use quasi-classical trajectory simulations to estimate the reaction rates, which qualitatively explains the observed results.