Configuration for scanning drift tube apparatus: Time-of-flight (TOF) experiment; ultraviolet laser light pulse: 1.7 µJ, 5 ns; cathode: Mg disk on a stainless steel electrode with 105 mm diameter; detector: grounded nickel mesh and stainless steel electrode 1 mm behind it; drift length: 7.8 to 58.3 mm; reduced electric field (E/N): 1 to 1790 Td; base pressure: ~1 x 10^-7 mbar; working gas pressure: 5 to 1000 Pa; averaging: 20000 to 150000 pulses uri icon