MOLECULAR AND IONIC CLUSTERS IN SATURATED VAPOR OVER LUTETIUM TRICHLORIDE

A Knudsen cell mass spectrometric technique was used to study both the neutral and charged species species that are in equilibrium in satura ted vapor over lutetium trichloride. It was found that in the temperat ure range between 885 and 1100 K the vapor is comprised of molecular ( LuCl3)(n) and ionic Cl-(LuCl3)(n) clusters where n = 1-6. For neutral constituents, monomer and dimer molecules are the most abundant, the p artial pressure of Lu2Cl6 being about 22 per cent with regard to the t otal pressure at 1000 K. According to thermodynamic calculations dimer molecules become the dominant species of the equilibrium vapor above 1200 K, In the temperature range studied, the temperature dependencies of partial vapor pressures (atm) of monomer, dimer, trimer and tetram er molecules are approximated by the following equations ln P(LuCl3) = (-31.4 +/- 0.6) x 10(3)/T + (18.8 +/- 0.5), ln P(Lu2Cl6) = (-42.5 +/- 0.7) x 10(3)/T + (28.7 +/- 0.6), ln P(Lu3Cl9) = (-48.3 +/- 1.2) x 10( 3)/T + (27.0 +/- 1.2), ln P(Lu4Cl12) = (-46.8 +/- 1.2) x 10(3)/T + (22 .9 +/- 1.2). Ion molecule equilibria have been studied in the temperat ure range 1000-1100 K and the temperature dependencies of equilibrium constants hare been obtained, Enthalpies of sublimation to monomer and polymer molecules, enthalpies of formation of gaseous molecules and i ons were evaluated using the second and third laws of thermodynamics. The selected values (298 K, kJ mol(-1)) are as follows: [GRAPHICS] The electron affinity of LuCl4 superchloride molecule has been estimated to be 3.7 +/- 1 eV. (C) 1997 by John Wiley & Sons, Ltd.