Machine C has undergone several changes since it was first built. Initially, the machine was used to perform coincidence studies of dissociative photodetachment (DPD) of anions, a technique pioneered in this lab. Information regarding these studies can be found here. Experiments involving dissociative recombination were also attempted on this machine. Information on that experiment can be found here. The most recent experimental work on Machine C involved dissociative charge exchange which has led to several important insights into dissociation mechanisms and dynamics of highly excited electronic states of small molecules.
This machine is currently undergoing another transformation to study dissociative photodetachment with a twist. For basic information how the DPD experiments are carried out see the Machine A page. In this case a cryogenic (10K) electrostatic ion beam trap has been added to the detection region. Anions will be trapped for several seconds at the full beam energy, up to 16keV, and will radiatively cool to ground vibrational and low rotational states free from re-excitation by warm blackbody photons. This will enable energetics and dynamics in DPD experiments to be determined more accurately as well as to study cooling processes of molecules on long (>millisecond) time scales, particularly through dipole forbidden transitions. Additionally, this trap could also lead to studies of the dissociation of state-prepared ions, and will enable laser-based coherent control and alignment experiments to be performed on ions with well-characterized quantum states.
The new Machine C will feature the same unique quadrant crossed delay line neutral detector as before for detection of up to 8 neutral fragments from a single dissociation event, as well as a wedge and strip anode-based velocity mapping electron detector within the trap cavity for detection of electrons ejected over the full 4pi solid angle. The interaction of the laser pulse and ion packet will occur at the center of the trap inside the electron detector, and the same cold packet of ions will repeatedly be probed until a majority of the ions are lost due to dissociation or scattering/charge exchange with background gas, expected to be ~1E-11 torr.
Pictures of the transformation of Machine C can be found here.
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