Thermodynamic properties of neutral and charged species in high-temperature vapour over terbium and thulium trichlorides
Lev Kudin, Alexander Pogrebnoi, Iljas Khasanshin, Vladimir Motalov
A Knudsen-cell mass spectrometric technique was used to study a composition of saturated vapour over terbium and thulium trichlorides. For the first time the various neutral (LnCl3)n and charged Cl–(LnCl3)n (Ln = Tb, Tm,n =1 – 8) species have been found in the temperature range between 900 and 1100 K. The partial vapour pressures of neutral constituents have been measured and the sublimation (DsH°) and the formation (DfH°) enthalpies of gaseous molecules and ions have been determined by means of the second and third laws of thermodynamics. The recommended values of DsH° (298 K)/kJ mol-1 are as follows: 290 ± 6 (TbCl3), 291 ± 5 (TmCl3), 365 ± 20 (Tb2Cl6), 361 ± 10 (Tm2Cl6), 414 ± 40 (Tb3Cl9), 419 ± 15 (Tm3Cl9), 400 ± 20 (Tm4Cl12), 365 ±60 (Tm5Cl15). The values of DfH° (298 K)/ kJ mol-1 are as follows: -709 ± 6 (TbCl3), -697 ± 6 (TmCl3), -1632 ± 15 (Tb2Cl6), -1615 ± 10 (Tm2Cl6), -2582 ± 40 (Tb3Cl9), -2545 ± 15 (Tm3Cl9), -3552 ± 20 (Tm4Cl12), -4575 ± 50 (Tm5Cl15), -1233 ± 20 (TbCl–4), -1239 ± 16 (TmCl–4), -2180 ± 35 (Tb2Cl–7), -2151 ± 22 (Tm2Cl–7), -3138 ± 40 (Tb3Cl–10), -3093 ± 23 (Tm3Cl–10), -4161 ± 50 (Tb4Cl–13), -4105 ± 24 (Tm4Cl–13), -5139 ± 60 (Tb5Cl–16), -5022 ± 60 (Tm5Cl–16), -6097 ± 25 (Tm6Cl–19), -8083 ± 80 (Tm8Cl–25).