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A new method to determine the mean adsorption lifetime of alkali metal halide molecules on a hot metal surface

1985; Elsevier BV; Volume: 65; Issue: 3 Linguagem: Inglês

10.1016/0168-1176(85)87006-3

1873-2801

Hiroyuki Kawano, Tsutomu Kenpō,

Advanced Chemical Physics Studies

The emission current of Li+ ions produced from LiI molecules incident upon a polycrystalline rhenium surface heated to 1157 K at a residual gas pressure of ∼ 2×10−7 torr was measured as a function of elapsed time after opening or closing a sample beam shutter. Within ∼6 s after stopping a beam incidence (6.66×1013 molecules cm−2 s−1), the Li+ current increased by 3.86 times and then decreased to zero. This change was analyzed using our original theory on thermal ionization, thereby leading to the conclusions: (1) the increase is caused by an increase in work function up to 5.99 eV according to a decrease in surface density of LiI (neither Li nor Li+), (2) the percentages of those particles (Li+, Li, and LiI) emitted during the 6 s are 36.6, 2.1 and 61.3%, respectively, and (3) the mean adsorption lifetime of LiI on the surface covered with residual gas molecules is 3.23 s, which is much longer than that of Li+ (<0.2 s). This new and simple method does not require the detection of emitted neutral particles (LiI and/or Li) and may be readily applicable to other sample-molecule/metal-surface systems under such an experimental condition that the emission current is appreciably increased after closing the shutter.