Dynamics of Carbonium Ions Solvated by Molecular Hydrogen: CH 5 + (H 2 ) n ( n = 1, 2, 3)

The dynamics of the carbonium ion (CH 5 + ), a highly reactive intermediate with no equilibrium structure, was studied by measuring the infrared spectra for internally cold CH 5 + (H 2 ) n ( n = 1, 2, 3) stored in an ion trap. First-principle molecular dynamics methods were used to directly simulate the internal motion for these ionic complexes. The combined experimental and theoretical efforts substantiated the anticipated scrambling motion in the CH 5 + core and revealed the effect of the solvent molecular hydrogen in slowing down the scrambling. The results indicate the feasibility of using solvent molecules to stabilize the floppy CH 5 + ion in order to make it amenable to spectroscopic study.