Knowledge Bank

Femtosecond pulses in the deep uv (near 200 nm) have been used to directly measure The $B~$ state lifetimes for gas phase $CH3I$ and $CD3I$ by time-resolved MPI. Tunable deep uv femtosecond excitation pulses were generated by sum frequency generation in BBO of a frequency doubled CPM laser with amplified portions of continuum. For the vibrationless state of $CH3I(CD3I)$ the lifetime is 1.38 ps (1.84 psec). It is longer for the $\nu 3=1$ level of $CH3I$ (1.80 ps). These values indicate the multidimensional nature of the dissociation and their isotopic and mode dependence will be compared with those obtained by indirect measurements.