Experimental

The experiments were carried out in a UHV metal installation: a magnetic sector mass-spectrometer with a residual pressure < 5 x 10-10 Torr was used for surface studies by the methods of TDS, surface ionization and thermo-ionic emission.12 Flows of Tm atoms and CsCl molecules were supplied to the substrate from a Knudsen cell and could be made to overlap. The ions or electrons emitted from the ribbon's 4 mm long central part were measured by a collector system. Parts of the ions entered the mass analyzer through a slit in the collector and detected at the analyzer exit by means of an ion-electron multiplier.

The used samples were directly heated the polycrystalline rhenium ribbons of 40 x 1.5 x 0.02 mm3 dimensions, which were textures by passing them trough an AC current. The work function of the ribbon, 9, was (5.15 ± 0.05) eV, which coincides with the value of 9 for the (1010) face of the Re.13

The Re ribbon was covered by a graphite layer at a substrate temperature of 1,600~1,790 K by admission of benzene vapour at a pressure of 10-5 Torr, until the electron emission reached a high and stable value, indicating a work function in the range 4.3~4.4 eV.

The kinetics of the reaction between Z (K, Na, Li) atoms and CsCl molecules with different T, vZ and vCsCl were experimentally investigated via the following two characteristics14-16: 1. The efficiency of reaction,

VCsCl VCsCl where i/CsCl is the density of inverse molecule flow, desorbed from the emitter and uninvolved in the reaction. The difference Vcsci — Vc sci(T) is equal to the amount of Cs atoms, separated during the reaction, as the CsCl molecules are not reflected from the 2DGF. These atoms are desorbed as Cs+ ions by surface ionization on 2DGF in the temperatures higher than the threshold temperatures for the light ionization of Cs on 2DGF.

2. The utilization factor of Tm atoms in reaction, is

VT m where v'Cs+ (T) is the density of the flow of Cs atoms appearing in the reaction, that desorbed from surface as Cs+ ions; vTm is the density of flow of Tm atoms to surface.

According to Eqs. (1) and (2), tf(T) and Q(T) are related by a similar relationship:

VT m

The method of steady-state flow provides that the concentration of particles on the surface is constant and is highly sensitive at the transformation of evaporated particles into ions through light surface ioniza-tion. In this case every particle evaporated from the surface becomes the ion and this is inaccessible to other forms of ionization. Light surface ionization takes place at evaporation of Cs atoms from the 2DGF on Re.

The atoms emerged from the surface are passive relative to dissociation of CsCl molecules and do not enter chemical reaction with reagents and weakly affect the composition of the reaction products.

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