Abstrakt
We have investigated different effects caused by clustering and multiphoton processes in the photodissociation of CH3Cl using velocity map imaging (VMI). Single-photon dissociation of CH3Cl at 193.3 nm yields CH3 and Cl fragments probed subsequently by resonance enhanced multiphoton ionisation (REMPI) at 333.52 nm and 235.31 nm, respectively.
In the clusters, the CH3 fragments are strongly 'caged' losing most of their kinetic energy. Consequently, the VMI is dominated by a sharp central peak.
On the other hand, the Cl fragments lose a broad range of energies in the cluster, yielding a blurred isotropic 'central blob' in VMI. At an increased 193 nm photon flux, another central feature appears in the CH3 images for isolated CH3Cl molecules.
This 'hour-glass' shaped image corresponds to the CH3Cl multiphoton ionisation at 193 nm and subsequent CH3Cl+ ion photodissociation at 333 nm. The ion photodissociation is a parallel process with the anisotropy β-parameter values between +1.3 and +2.0.
The total kinetic energy release (TKER) distribution suggests a high CH+3 vibrational excitation. The CH3Cl+ ion photodissociation is discussed and compared to the photodissociation of similar CH3Br+ ion.