“…Another possibility is to use hydrogen gas, H 2 , which has been used more often than argon and which is the focus of the present computational work. For the similar anion, CN − , we had found earlier that the rotationally inelastic rate coefficients for collisions with H 2 were even larger than those for argon, leading to fast thermalisation times [34], thereby suggesting H 2 may also be suitable as an efficient buffer gas for C − 2 . Hydrogen gas has the advantage of being usable down to about 10 K before freezing out.…”