Field ionization detection of supersonic molecular beams

Seminal field ionization detection of a supersonic helium beam is reported, including intensity measurements on a continuous beam and time-of-flight measurements on a chopped beam. Also unique to these experiments is the care with which the field ionization tip was prepared and characterized prior to its use. Comparative measurements on a static helium gas are presented and the effective detection area of the field ionization tip is extracted for both beam and static gas. These areas are much smaller than those reported in previous experiments, suggesting that detection efficiency depends strongly on energy and momentum transfer during the initial atom–tip collision.