title: Validation of velocity map imaging conditions over larger areas.
abstract: We have established through simulations and experiments the area over which Velocity Map Imaging (VMI) conditions prevail. We designed a VMI setup in which we can vary the ionization position perpendicular to the center axis of the time-of-flight spectrometer. We show that weak extraction conditions are far superior over standard three-plate setups if the aim is to increase the ionization volume without distorting VMI conditions. This is important for a number of crossed molecular beam experiments that already utilize weak extraction conditions, but to a greater extent for surface studies where fragments are desorbed or scattered off a surface in all directions. Our results on the dissociation of NO2 at 226 nm show that ionization of the fragments can occur up to ±5.5 mm away from the center axis of the time-of-flight spectrometer without affecting resolution or arrival position.
authors: School of Chemistry, The University of Manchester, Manchester, United Kingdom.
authors: Mike
authors: M
authors: Reid
authors: Sven P K
authors: SP
authors: Koehler
mesh_terms: D009569:Nitric Oxide / Q000737:chemistry*; D061848:Optical Imaging / Q000295:instrumentation / Q000379:methods*; D013057:Spectrum Analysis / Q000295:instrumentation / Q000379:methods*
chemical_list: D009569:Nitric Oxide