Thermodynamic study of the gaseous dilanthanum carbides, La2C2, La2C3, La2C4, La2C5, La2C6, and La2C8 by high temperature mass spectrometry

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Abstract
The high temperature Knudsen effusion mass spectrometric technique has been used to identify and characterize the molecules La2C2, La2C3, La2C4, La2C5, La2C6 and La2C8 in the equilibrium vapor above the La–Ir–graphite system. The enthalpies ΔH°0 of the reaction 2La(g) +n C(graph.)=La2Cn (g) (n=2–6, 8) were evaluated using the third law method. For La2C3(g) and La2C4(g) a second law evaluation was also performed, indicating the linear symmetric structure as the most probable. The selected values for the reaction enthalpies were combined with ancillary literature data to yield the atomization energies ΔH°a,0, and the standard heats of formation ΔH°f,298.15 in kJ mol−1 of the gaseous dilanthanum carbides: La2C2 La2C3 La2C4 La2C5 La2C6 La2C8 UFRULE1 ΔH°a,0 1670±40 2339±27 3060±21 3703±50 4395±50 5658±60 ΔH°f,298.15 621±40 658±27 648±21 717±50 737±50 898±60