  Strong-field ionization, involving tunnel ionization and electron
rescattering, enables femtosecond time-resolved dynamics measurements of
chemical reactions involving radical cations. Here, we compare the formation of
CH3S+ following the strong-field ionization of the isomers CH3SCN and CH3NCS.
The former involves the release of neutral CN, while the latter involves an
intramolecular rearrangement. We find the intramolecular rearrangement takes
place on the single picosecond timescale and exhibits vibrational coherence.
Density functional theory and coupled-cluster calculations on the neutral and
singly ionized species help us determine the driving force responsible for
intramolecular rearrangement in CH3NCS. Our findings illustrate the complexity
that accompanies radical cation chemistry following electron ionization and
demonstrate a useful tool for understanding the cation dynamics after
ionization.
