Magnetic sublevel coincidence spectroscopy and characterisation of the 3(1)D state of Helium

Instrumentation, techniques and a statistical analysis are described for th e accurate observation of the two, and three, particle coincidences of the scattered energy loss electrons with the two sequential cascading photons f rom the 3(1)D state of helium excited by incident electrons. A three-dimens ional histogram data accumulation system enables the two, and three, partic le true and random coincidences to be analysed. These observations yield in formation not obtainable in other ways and were used to deduce the scatteri ng amplitudes, relative phases and their various combinations for the excit ed 3(1)D state. The measured values agree with the best convergent close co upling calculations within one standard deviation experimental uncertainty. (C) 1998 Elsevier Science B.V. All rights reserved.