Terbium vapor pressure

Data reported in Table 47 show that the ArH°(298) values calculated by the second and third laws from the results of systematic tensiometric measurements of saturated vapor pressures presented in the semilogarithmic representation (Polyachenok, 1972) differ from each other by no more than 15 kj/mol. However, variation of AfH°(298), calculated by the third law, as a function of the number of the lanthanide in the series sharply increases for gadolinium and terbium, then decreases in going down the series from Dy to Yb, and finally increases again for lutetium. 

One possible reason for such the discrepancy between the Pm/Pd values found from the semilogarithmic representations and mass spectral data is that the evaporation of the samples is incongruent. This is demonstrated by measuring the pressures of the saturated vapor over samarium trichloride (Pogrebnoi et al., 2001) and terbium trichloride (Khasanshin et al., 1999). 

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