Br's orbitals are filled here because it's covalently bonded to a carbon, so it's basically krypton. Experiments with moving atoms around on surfaces with STMs are always done at cryogenic temperatures because that's the only way to do them.

>. Hence, the Br atoms kept the molecules on track, likely because their interaction with the surface substantially contributed to the barrier for molecular rotation

Yeah that's a reason people prefer AFM (but then they won't be able to do manipulation)?

[Br- is a "good leaving group", not so much at 7K maybe. You are also right in that, above all, they don't want their molecule sticking (irreversibly) to the (tungsten) tip ]