Tin clusters adopt prolate geometries

We have characterized the structures of ${\mathrm{Sn}}_n$ cations up to $n=68\mathrm{}$ using ion mobility measurements. Up to $n\sim 35,$ tin clusters track the prolate growth pattern previously found for ${\mathrm{Si}}_n$ and ${\mathrm{Ge}}_n.$ However, the detailed size-dependent variations start deviating from those observed for ${\mathrm{Si}}_n$ above $n=14\mathrm{}$ and ${\mathrm{Ge}}_n$ above $n=21.\mathrm{}$ Over the $n\sim 35–65$ size range, tin clusters gradually rearrange towards near-spherical geometries, passing through several intermediate structural families. Two or three isomers are resolved for some sizes in the $n=18\mathrm{}–49$ range. The observed geometries are independent of the He buffer gas temperature between 78 and 378 K and are not affected by collisional annealing.