Perspective: Advanced particle imaging

Abstract

Since the first ion imaging experiment [D. W. Chandler and P. L. Houston, J. Chem. Phys. 87, 1445-1447 (1987)], demonstrating the capability of collecting an image of the photofragments from a unimolecular dissociation event and analyzing that image to obtain the three-dimensional velocity distribution of the fragments, the efficacy and breadth of application of the ion imaging technique have continued to improve and grow. With the addition of velocity mapping, ion/electron centroiding, and slice imaging techniques, the versatility and velocity resolution have been unmatched. Recent improvements in molecular beam, laser, sensor, and computer technology are allowing even more advanced particle imaging experiments, and eventually we can expect multi-mass imaging with co-variance and full coincidence capability on a single shot basis with repetition rates in the kilohertz range. This progress should further enable "complete" experiments-the holy grail of molecular dynamics-where all quantum numbers of reactants and products of a bimolecular scattering event are fully determined and even under our control.

FIG. 1.

Schematic drawings and first images obtained using particle imaging. On the top row, left, is the drawing of the expected three-dimensional distribution from an instantaneous dissociation for a parallel transition to a repulsive state, as is the case for the methyl iodide, CH₃I, dissociation. Top row middle is a drawing of the expected two-dimensional projection of the three-dimensional velocity distribution. Top row right is an artist’s rendition of the inverse Abel transformed distribution obtained from analyzing the 2-dimensional projection. The bottom row shows the black and white raw data (left), the digitized and false colored raw data (middle), and the inverse Abel transform of the image (right) of the CH₃I dissociation at 266 nm with the detection of CH₃ by laser ionization at 330 nm.