DISSOCIATION-ENERGY AND ENTHALPY OF FORMATION OF GASEOUS SILVER DIMER

The equilibrum Ag2(g) = 2Ag(g), has been measured by Knudsen cell mass spectrometry, and thermal functions for Ag2(g) have been evaluated from new spectrometric data. From these data the dissociation energy of Ag2(g) has been calculated and combined with reevaluated previous experimental data to obtain the selected value of D-degrees 0[Ag2(g)] = 158.0 +/- 3.4 kJ mol-1 or DELTAH-degrees a,298.15[Ag2(g)] = 160.3 +/- 3.4 kJ mol-1. From these together with pertinent literature data the standard enthalpy of formation, DELTAH(degrees) f,298.15[Ag2(g)] = 409.9 +/- 3.5 kJ mol-1 and the dissociation energy of Ag2+, D(degrees)0[Ag2+(g)] = 166.1 +/- 3.4 kJ mol-1 have been derived. It has been noticed that the dependence of the ratio of the monomer/dimer ionization cross section on the energy of the ionizing electrons affects the determination of the pressure constants and hence the dissociation energy remarkably.