High-resolution ion time-of-flight analysis for measuring
molecular velocity distributions
Y. Kim, S. Ansari, B. Zwickl, and H. Meyer
Department of Physics and Astronomy, The University of Georgia, Athens, Georgia 30602-2451
A new electrode setup for high-resolution ion time-of-flight (TOF) analysis is described. The setup is used in combination with a counterpropagating pulsed molecular-beam scattering apparatus and laser ionization to measure one-dimensional velocity distributions of low-energy molecular products resulting from scattering or dissociation processes. In the case of ensembles characterized by cylindrical symmetry with respect to the molecular-beam axis, measured TOF spectra represent the angular distribution of the products. In the imaging of the ions onto the detector, this symmetry is preserved by using a pair of electrostatic mirrors for the deflection. Combined with separate velocity dispersion and acceleration fields, the present arrangement achieves superior resolution and detection efficiency. Although the resolution of the setup is limited by the velocity distribution of the molecular-beam pulses, changes in the average local velocity as small as 10 m/s have been observed.
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