A vibrationally resolved negative ion photoelectron spectrum of Nb8

The 488 nm negative ion photoelectron spectrum of Nb-8, obtained at an instrumental resolution of similar to 5 meV, displays a clear vibrational progression in a mode with a frequency of 180 +/- 15 cm(-1) in neutral Nb-8 and 165 +/- 20 cm(-1) in Nb-8(-). The normal mode displacement of 0.4 +/- 0.1 u(1/2) Angstrom indicates a very small geometry change upon electron detachment. The electron affinity of Nb-8 is 1.513 +/- 0.008 eV. These results are discussed in light of previous negative ion photoelectron spectroscopic and density functional studies of Nb-8 and Nb-8(-). (C) 2000 Elsevier Science B.V.