Thermodynamic stability of the molecules YC2, YC3, YC4, YC5, YC6, YC7, and YC8 by high temperature Knudsen effusion mass spectrometry

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Abstract
The molecules YC2, YC3, YC4, YC5, YC6, YC7, and YC8 have been observed in a Knudsen effusion mass spectrometric investigation of the gas phase above the Y–Ir–Au–graphite system. The enthalpies ΔH○0 of the reactions Y(g)+n C(graph)=YCn(g)(n=2–8) were evaluated by the third law method; the second law method was employed for the gaseous molecules with up to six carbon atoms. The selected values of the reaction enthalpies ΔH○0 were combined with ancillary literature data to yield the atomization enthalpies ΔH○a,0 and the standard enthalpies of formation ΔH○f,298.15 in kJ mol−1 of the gaseous yttrium carbides. The values of ΔH○0 and ΔH○a,0 (in kJ mol−1) are 197±5 and 1225±8 for YC2; 377±10 and 1757±12 for YC3; 361±8 and 2484±10 for YC4; 499±10 and 3057±15 for YC5; 536±15 and 3731±20 for YC6; 684±35 and 4294±35 for YC7, and 693±35 and 4727±35 for YC8. The values of ΔH○f,298.15 (in kJ mol−1) are 623±8, 804±12, 790±10, 924±15, 966±20, 1105±35, and 1124±35 for YCn (n=2–8), respectively.

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