Spin-Orbit State-Selective C-I Dissociation Dynamics of the CH₃I⁺ X Electronic State Induced by Intense Few-Cycle Laser Fields

Studies of ultrafast molecular dynamics induced by intense laser fields can reveal new approaches to manipulating chemical reactions in the strong-field regime. Here, we show that intense few-cycle laser pulses can induce the spin-orbit state-selective C-I dissociation of the iodomethane cation (CH₃I⁺) in the X electronic state. Irradiation of CH₃I by 6 fs laser pulses with peak intensities of 1.9 × 10¹⁴ W/cm² followed by femtosecond extreme ultraviolet probing of the iodine 4d core-level transitions reveals dissociation of the CH₃I⁺ X ²E_1/2 state with a time constant of 0.76 ± 0.16 ps. By contrast, the X ²E_3/2 spin-orbit ground state does not exhibit any appreciable dissociation on the picosecond time scale. The observed spin-orbit state-selective dissociation of the X state is rationalized in terms of the laser-induced coupling to the à state. Our results suggest that the intense-laser control of photodissociation channels can be potentially extended to spin-orbit split states.