Atomization energies of gaseous AlPd and Al2Pd

Abstract

Knudsen cell mass spectrometry has been used to investigate the gaseous equilibrium reactions (1) AlPd(g)⇌ Al(g)+ Pd(g) and (2) Al₂Pd(g)+ Pd(g)⇌ 2AlPd(g). The reaction enthalpies ΔH⁰₀ are (1) 250.6 ± 12.0 kJ mol^–1 and (2)–8.8 ± 3.0 kJ mol^–1 where the second and third law procedures were used to obtain the value for reaction (1) and the third law procedure for reaction (2). The atomization energies derived from these reaction enthalpies are: D⁰₀(AlPd)= 250.6 ± 12.0 kJ mol^–1 and D⁰₀(Al₂Pd)= 492.4 ± 24 kJ mol^–1. The corresponding standard heats of formation, ΔH⁰_f,298 are AlPd: 451.8 ± 12.5 kJ mol^–1 and Al₂Pd: 536.4 ± 24.3 kJ mol^–1. The bonding in these molecules is discussed in terms of empirical models.