Clustering and multiphoton effects in velocity map imaging of methyl chloride

Abstract

We have investigated different effects caused by clustering and multiphoton processes in the photodissociation of CH${}_3$Cl using velocity map imaging (VMI). Single-photon dissociation of CH${}_3$Cl at 193.3 nm yields CH${}_3$ and Cl fragments probed subsequently by resonance enhanced multiphoton ionisation (REMPI) at 333.52 nm and 235.31 nm, respectively. In the clusters, the CH${}_3$ 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 CH${}_3$ images for isolated CH${}_3$Cl molecules. This ‘hour-glass’ shaped image corresponds to the CH${}_3$Cl multiphoton ionisation at 193 nm and subsequent CH${}_3$Cl${}^{+}$ 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 CH${}_3$Cl${}^{+}$ ion photodissociation is discussed and compared to the photodissociation of similar CH${}_3$Br${}^{+}$ ion.

GRAPHICAL ABSTRACT

KEYWORDS:

• Photodissociation
• molecular clusters
• solvent effects
• multiphoton ionisation
• energy transfer

Acknowledgments

We acknowledge the support of the Czech Science Foundation (GAČR) project No.: 19-14105S and also Praemium Academiae of the Czech Academy of Sciences. We are also very grateful to Dave Parker, thanks to whom we have been invited to join the VMI community in 2009 within a European ITN network. We really enjoyed being part of this group of very nice people and excellent scientists, and we have benefited from that in many respects: notably, we have learned and introduced the VMI technique in our experiments in Prague. We really appreciate that Dave has always been very friendly and supportive to our group.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by Grantová Agentura České Republiky [grant number 19-14105S].