Model of reactive collisions in a cryogenic buffer gas cell*

Chemical reactions in buffer gas cells have been previously performed via exothermic reactions or endothermic reactions whose barriers were overcome via the excitation of the reacting metal. Recently, the highly endothermic reaction between Ca atoms and an H₂ buffer gas has been notably achieved to produce a large flux of CaH in a buffer gas cell without the need to electronically excite Ca [1]. We develop a reaction network to describe the dynamics in a buffer gas cell, using reaction rates from quasi-classical trajectory simulations, properly predicting the yield of CaH. We find that the inclusion of internal states is critical to describing the facilitation of endothermic reactions in cryogenic buffer gas beam environments.

[1] Sun, Q., Dai, J., Koots, R., Riley, B., Pérez-Ríos, J., Mitra, D., & Zelevinsky, T. (2025). Chemistry in a cryogenic buffer gas cell. arXiv preprint arXiv:2501.05613.