The dissociation energies of gaseous BaPd and BaRh and calculated dissociation energies of selected diatomic group IIA–platinum metal intermetallic molecules

The high‐temperature Knudsen effusion mass spectrometric technique has been used to measure the second law and third law enthalpies of the reactions BaPd(g) =Ba(g)+Pd(g) and BaAu(g)+Pd(g) =BaPd(g)+Au(g). The third law enthalpies ΔH°₂₉₈ (in kJ) have been obtained as 224.3±2.4 and 35.8±1.8. The corresponding second law values are 216.8±8.9 and 30.9±9.8 kJ, respectively. From these reaction enthalpies the following thermodynamic properties in kJ mol⁻¹ (kcal mol⁻¹) were derived: D°₂₉₈[BaPd(g)]=221.8±5.0 (53.0±1.2), D°₀[BaPd(g)]=220.0±5.0(52.6±1.2), ΔH_f,298[BaPd(g)]=336.8±10 (80.5±2.5), and °H_f,0[BaPd₍g)]=338.5±10 (80.9±2.5). The dissociation energy of BaRh in kJ mol⁻¹ (kcal mol⁻¹) has been determined as D°₀[BaRh(g) =257.4±25 (61.5±6.0) or D°₂₉₈[BaRh(g)]=259.4±25 (62.0±6.0). The dissociation energies of BaPd and BaRh have been interpreted in terms of an empirical valence bond approach assuming double bond formation and utilizing a 5d orbital of barium in BaPd. Values for the bond energies of the diatomic molecules of barium with the platinum metals and of SrPt calculated by the model are also given.