Vaporization and Surface lonization of LaC2, CeC2, PrC2, NdC2, ThC2 and UC2

Abstract

The Langmuir vaporization and the surface ionization of LaC2, CeC2, PrC2, NdC2, ThC2 and UC2 from a heated graphite filament have been studied mass spectrometrically. It was found that there were present small amounts of neutral and ionic metal dicarbide molecules in addition to neutral and ionic metal atoms in the LaC2, CeC2, PrC2, ThC2 and UC2-C systems with the exception of NdC2-C, where neither neutral nor ionic metal dicarbide molecules were observed. The reason for this exceptional behavior of the NdC2-C system is explained by the very small vaporization coefficients, as estimated from the measurements of neutral MC2/M ratios and ionic MC2/M ratios. From the measurements of the heats of vaporization, it was surmised that the ionization potential of Th measured by the surface ionization comparison technique might be too high.