Predissociation dynamics of B state of methyl iodide with femtosecond pump-probe technique

The predissociation dynamics of B Rydberg state of methyl iodide is studied with femtosecond two-color pump-probe time-of-flight spectra at pump pulse of 400 nm and probe pulse of 800 nm. The dominant product channels are the CH3I+ and CH3+ formation. The time-dependent signals for CH3I+ and, CH3+ ions are obtained. Both of the signal curves can be fitted by biexponential decays with time constants of tau(1) and tau(2), tau(1) is assigned to the lifetimes of high Rydberg states, which can be accessed by absorbing three 400 nm pump pulses and tau(2) reflects the dynamics of B Rydberg state, which is accessed with two pump pulses. The lifetime of B Rydberg state is determined to be about 1.57 ps, which is incredibly consistent with the previous studies. The results were interpreted as a multiphoton dissociative ionization processes.