Measurements of transport coefficients for lithium ions in argon and helium ions in helium with a drift-tube mass spectrometer

Abstract

A drift-tube mass spectrometer for precision measurements of transport coefficients for ions in gases is described. The apparatus has been used to determine the ratio DT/ mu between the transverse diffusion coefficient and the mobility for He+ ions in the helium at 294 K and 15<or=E/n0<or=2000 Td, by direct measurement of transverse current density distributions of mass-analysed ions. The apparatus has also been used to determine the drift velocity Vdr and the ratio DL/ mu between the longitudinal diffusion coefficient and the mobility for Li+ ions in argon at 295 K and 40<or=E/n0<or=400 Td and the ratio DT/ mu for Li+ ions in argon at 294 K and 15<or=E/n0<or=550Td, using the Townsend method. Good agreement was found between the present experimental results and recent calculations from at initio potentials.