THE BOND-ENERGY OF RH-2

In a spectroscopic investigation of jet-cooled Rh-2 by the resonant tw o-photon ionization method, an abrupt predissociation threshold is obs erved in a dense set of vibronic levels at 19 405+/-4 cm(-1) Based on the high density of states expected in the rhodium dimer, the sharp de finition of the predissociation threshold that is observed, and the va lidation of a similar conclusion in the case of V-2, it is argued that predissociation occurs as soon as the energy of the separated ground state atoms is exceeded. On this basis the bond energy of Rh-2 is assi gned as D-0(Rh-2)=19405+/-4 cm(-1)=2.4059+/-0.0005 eV. This value is c ompared to the results of other experiments and to theoretical calcula tions. The bond energy of disilver, D-0(Ag-2)=1.65+/-0.03 eV, provides a particularly useful standard of comparison, and suggests that 4d co ntributions to the bond energy of Rh-2 amount to at least 0.76 eV. (C) 1998 American Institute of Physics.