Channel competition in strong-field dissociation of CS$^+$*

We study intense ultrafast laser-induced dissociation of a CS$^+$ ion beam, utilizing a coincidence 3-D momentum imaging technique. Over a laser intensity range of 10$^{10}$--10$^{16}$ W/cm$^2$, we find clear intensity-dependent behavior of the C$^+$+S and C+S$^+$ branching ratios. Specifically, we observe that the branching ratios are nearly equal at low intensities ($\sim$10$^{10}$--10$^{12}$ W/cm$^2$) and deviate from each other at higher intensities ($>$10$^{13}$ W/cm$^2$), where C+S$^+$ dominates. We propose that the low-intensity branching ratio behavior is due to strong mixing of states corresponding to the relevant dissociation limits mediated by the non-adiabatic couplings, and we identify possible dissociation pathways involving these couplings. Another aspect of channel competition, closing and opening of the two dissociation channels as a function of total energy, is distinctly observed, and this behavior is characterized using the well-known Wigner law for near-threshold behavior [1,2]. \\[4pt] [1] E. P. Wigner, Phys. Rev. \textbf{73}, 1002 (1948).\\[0pt] [2] H. R. Sadeghpour \emph{et al.}, J. Phys. B \textbf{33}, R93 (2000).