Studies Of The Ionization/dissociation Dynamics Of Cyclohexanone By Femtosecond Pump-Probe Technique

We report an experimental study of the dissociation dynamics of cyclohexanone performed on a femtosecond laser pump (800 nm)-probe (800 nm) system, with time-of-flight mass spectrometer. The pump and probe pulses we used are obtained from a Ti:sapphire laser system.We measure the intensity of parent and fragments ions as a function of the delay time between Pump and Probe pulses. Through the integral of some ions intensity,we can get important information of photoionization dynamics. We fit the data with the aid of program that we wrote in Matlab. After deconvolution, the life times of parent and some fragments are obtained.Combining calculation with the experimental data, we define the ionization / dissociation process for the formation of parent ions, as well as the life time of some transient state. So that the mechanism of fragments generation is clear. By comparing the life times of some fragments, we find that some ions have very similar decay time: C₃H₆⁺(83±7 fs) and C₃H₃⁺(82±10 fs). This is a very important information for us,by which we can get the conclusion that the two ions come from a same excited state of parent ion.After absorption of m photons, the cyclohexanone molecule in ground state is excited to the excited state A* with a life time of 80 fs. Then A* may be ionized via absorbing photons to A⁺*, which will relax because of its instability. Before relaxation, A⁺* can be resonantly excited to higher excited state by the 800 nm laser pulse, and auto-dissociates further; while after relaxation, it can't absorb any photons, so it will relax to the ground state of ion A⁺.