Formation of the negative cluster ions in a Knudsen cell at low temperatures

Mass spectrometric determination of absolute pressures of the positive Na+, K+, Cs+ and the negative NaAl2F8−, AlF4−, Al2F7−, NaAl3F11−, Na2Al3F12− ions in the saturated vapor over the Na5Al3F14-AlF3 system was carried out at the temperature near 850 K. The measurements were made in a clean nickel effusion cell and in the same cell with the inner surface covered by cerium trifluoride. An increase of negative ion pressures at least three order of magnitude has been observed after CeF3 treatment as compared with a clean cell. At that time the pressure of positive ions decreased slightly. The result is explained by F− superionic conductivity of CeF3.