Preparation, characterization, and oxidation of small metal clusters

Abstract

Using primarily high flux oven-based metal source configurations small alkali (Li x , Na x , K x ), coinage (Cu x ,Ag x ), and group IVA (Si x ,Ge x ) metal clusters are being generated in supersonic expansions and agglomerating flows. Both the clusters and their oxidation to form the metal cluster oxides, M n O(n > 2), are being characterized using a combination of single and multiphoton laser fluorescent techniques, chemiluminescence, and mass spectrometry. Photodissociation studies on sodium trimer using laser-induced one- and two-photon atom fluorescence spectroscopy are now being extended to lithium trimer generating a bound-free mirror image spectroscopy which strongly complements the information obtained from bound-bound two-photon spectroscopy. Recent results obtained with an intense copper trimer source demonstrate an ability to (1) study fluorescence from strongly dissociative levels and (2) observe substantial temperature-dependent dynamic changes in spectral features associated with the fluxional nature of copper trimer. Using agglomerated cluster flows and taking advantage of previous experience in the study of chemiluminescent processes across a wide pressure range, we are probing the chemiluminescent emission resulting from the oxidation of small copper (Cu x + O3), silver (Ag x + O3), silicon (Si x + NO2, N2O,O3), and germanium (Ge x + O3, N2O) clusters. From these studies we have obtained the first quantal information on the energy levels and optical signatures of several metal cluster oxides and observed the manifestation of a unique dynamics associated with metal cluster oxidation processes.