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Temperature dependence of thermal positive ion production from sodium bromide molecules incident upon a glowing rhenium surface

1984; American Institute of Physics; Volume: 81; Issue: 3 Linguagem: Inglês

10.1063/1.447810

1520-9032

Hiroyuki Kawano, Tsutomu Kenpō,

Quantum Information and Cryptography

Emission current of Na+ ions produced from NaBr molecules impinging with a flux of 6.55×1013 molecules cm−2 s−1 upon a heated polycrystalline rhenium surface in the residual gas pressure of about 2×10−7 Torr was measured as a function of surface temperature (T) in the range of about 900–2100 K, thereby indicating that the sticking probability of NaBr to the surface is virtually unity and that the ionization efficiency ( β+) is ∼1 and 0.23 for T≂1100–1500 and 1800–2100 K, respectively. These results are explained reasonably by our previous theory that the degree (γ) of dissociation of incident molecules generally depends upon the ionization coefficient (α+) and hence upon the effective work function (φ+) for the positive ionization unless α+ is much smaller than unity. The value of φ+ was 5.45–5.51 eV for T≳1800 K, below which φ+ gradually increased up to ∼6.8 eV according to a decrease in T. By this increase both β+ and γ were kept at virtually unity even at a low temperature down to about 1100 K, at which they began to decrease sharply with a reduction in T because φ+ had already turned to a decrease at about 1200 K.