Picosecond MPI mass spectrometry of CH_3I in the process of dissociation

Picosecond multiphoton ionization and time-of-flight mass spectrometry has been used to monitor the dissociation of methyl iodide excited to its A continuum. The measured signals show a rapid buildup when the probe laser is tuned to a resonance of free atomic iodine and a sharp feature at zero time delay when it is tuned off-resonance. Enhanced signal is also observed in the parent ion channel. These results illustrate the possible use of this technique for the probing of fragment species before they are completely separated from their partners in a half-collision process.