CLUSTER STUDIES WITHIN A SUPERSONIC MOLECULAR BEAM
AbstractA novel technique for the production of metal and semiconductor clusters based on laser vaporization within the throat of a pulsed supersonic molecular beam nozzle has been developed within our lab. An outline of the overall experimental equipment and detection schemes used for both producing and probing the clusters within the beam will be delineated. A number of studies using this technique have been carried out in an effort to investigate some of the fundamental physical properties such as bonding and reactivities of these species.
The first set of spectroscopic investigations is concerned with the nature of the metal-metal bond in transition metal diatomics. Studies of certain homonuclear transition metal diatomics were conducted using high resolution resonant two-photon ionization spectroscopy in an effort to obtain gas phase data on both the ground state bond lengths and vibrational frequencies of these species. These investigations, as exemplified by chromium dimer, attempted to determine the contribution of the d-orbitals to bonding. Also, data from similar studies on V(,2), Mo(,2), and Ni(,2) is represented in tabular form.
Subsequently, our spectroscopic investigation of the astrophysically important triatomic molecule, silicon dicarbide, is detailed with the ultimate goal of this study being to determine the ground state and excited state bond lengths and geometries of this species. For the past thirty years, the geometry of this molecule was thought to be asymmetric and linear (Si-C-C), however, from the resulting data it is clear that silicon dicarbide is, in actuality, an asymmetric top of C(,2v) symmetry.
The recent development of a reaction tube that when coupled to the aforementioned cluster source has facilitated study of gas phase reaction chemistry on metal clusters (2-30 atoms). Details of this reaction tube and pertinent factors regarding gas conditions contained within the tube during the reaction period will be explained. Initial studies of the variation of reactivity as a function of cluster size have been performed using a select group of reactant molecules (CO, N(,2), H(,2)) and metals. This work has led to interesting results suggesting that a significant variation in reactivity does exist which depends on the metal, cluster size, and reactant