Investigation of the thermodynamic stability of the molecule LaIr(g) by high temperature mass spectrometry

Abstract

The high temperature Knudsen effusion mass spectrometric technique has been used to identify the previously unkown molecule LaIr in the gas phase over the La–Ir–Au–C(s) system. Evaluations of the enthalpy for the reaction LaIr(g) =La(g)+Ir(g) using the third and second law analysis yielded the following selected dissociation energy and standard heat of formation for the LaIr molecule. D°0(LaIr) =573±12 kJ mol−1 or 136±3 kcal mol−1, D°298(LaIr) =576±12 kJ mol−1 or 137±3 kcal mol−1, and ΔH°f,298(LaIr) =524±20 kJ mol−1 or 125±5 kcal mol−1. The dissociation energy of the gaseous molecule W2, which is isoelectronic with LaIr, is estimated to be 535±40 kJ mol−1 or 128±10 kcal mol−1.