Three-dimensional velocity map imaging: Setup and resolution improvement compared to three-dimensional ion imaging

Abstract

For many years the three-dimensional (3D) ion imaging technique has not benefited from the introduction of ion optics into the field of imaging in molecular dynamics. Thus, a lower resolution of kinetic energy as in comparable techniques making use of inhomogeneous electric fields was inevitable. This was basically due to the fact that a homogeneous electric field was needed in order to obtain the velocity component in the direction of the time of flight spectrometer axis. In our approach we superimpose an Einzel lens field with the homogeneous field. We use a simulation based technique to account for the distortion of the ion cloud caused by the inhomogeneous field. In order to demonstrate the gain in kinetic energy resolution compared to conventional 3D Ion Imaging, we use the spatial distribution of H(+) ions emerging from the photodissociation of HCl following the two photon excitation to the V (1)Sigma(+) state. So far a figure of merit of approximately four has been achieved, which means in absolute numbers Delta v/v = 0.022 compared to 0.086 at v approximately = 17,000 m/s. However, this is not a theoretical limit of the technique, but due to our rather short TOF spectrometer (15 cm). The photodissociation of HBr near 243 nm has been used to recognize and eliminate systematic deviations between the simulation and the experimentally observed distribution. The technique has also proven to be essential for the precise measurement of translationally cold distributions.

Proton formation dynamics in the REMPI[2+n] process via the F Δ12 and f Δ32 Rydberg states of HCl investigated by three-dimensional velocity mapping

“…The experimental setup has been described in two recent publications. 26,27 Thus, here we will give only a short summary and the facts relevant to the current experiment. A homebuilt TOF spectrometer mounted to a commercial threedimensional ͑3D͒ imaging detector consisting of a two stage micro channel plate and a delay line anode ͑RoentDek͒ 28,29 in a stainless steel vacuum vessel is the heart of the 3D velocity mapping apparatus.…”

Ion and velocity map imaging for surface dynamics and kinetics

“…Others have previously reported using position sensitive detection methods for studying surface scattering, 30 based on ion imaging [31][32][33] or velocity map imaging techniques, which were developed at around the same time as those for the gasphase imaging experiments. 34,35 These have predominantly used a geometry in which the surface and the detector are parallel, [36][37][38][39][40][41] which is convenient for the production of the imaging electric fields but prevents the projection of the full velocity distribution in the scattering plane onto the detector. Our new imaging setup (shown in Fig.…”

Resolving Strong Field Dynamics in Cation States of CO_2 via Optimised Molecular Alignment

“…There are two strategies for achieving this. Firstly, one may equip an anode based MCP detector with spatial resolution, for instance a delay line anode [182]. The second possibility is to add time resolution to an imaging MCP detector, which requires a time-sensitive read-out system of the phosphor screen.…”