Preparing transition-metal clusters in known structural forms: The mass-analyzed threshold ionization spectrum of V-3

The first results are presented of a new experiment designed both to generate and characterize spectroscopically individual isomers of transition-metal cluster cations. As a proof of concept the one-photon mass-analyzed threshold ionization (MATI) spectrum of V-3 has been recorded in the region of 44 000-45 000 cm(-1). This study extends the range of a previous zero-kinetic-energy (ZEKE) photoelectron study of Yang [Chem. Phys. Lett. 231, 177 (1994)] with which the current results are compared. The MATI spectra reported here exhibit surprisingly high resolution (0.2 cm(-1)) for this technique despite the use of large discrimination and extraction fields. Analysis of the rotational profile of the origin band allows assignment of the V-3 ground state as and the V-3(+) ground state as , both with D-3h geometry, in agreement with the density-functional theory study of the V-3 ZEKE spectrum by Calaminici [J. Chem. Phys. 114, 4036 (2001)]. There is also some evidence in the spectrum of transitions to the low-lying excited state of the ion. The vibrational structure observed in the MATI spectrum is, however, significantly different to and less extensive than that predicted in the density-functional theory study. Possible reasons for the discrepancies are discussed and an alternative assignment is proposed which results in revised values for the vibrational wave numbers of both the neutral and ionic states. These studies demonstrate the efficient generation of cluster ions in known structural (isomeric) forms and pave the way for the study of cluster reactivity as a function of geometrical structure. (c) 2005 American Institute of Physics