Structural dynamics of protonated methane and acetylene

The structural stability of protonated methane (CH5+) and acetylene (C2H3+) has been investigated with ab initio molecular dynamics. In CH5+, the hydrogen atoms execute large amplitude pseudorotational motions. The hydrogen migrations are not disturbed by complexation with a hydrogen molecule. In contrast, for C2H3+, the three hydrogen atoms permutate cyclically among the end carbon atoms and the bridging position. The theoretical results are consistent with and explain recent spectroscopic observation of these molecules.