‘Black-body’ radiation of free niobium clusters heated by oxidation

Niobium clusters generated via the laser vaporization technique with a size distribution centered around 260 atoms react with oxygen. Optical emission spectra have been recorded in the wavelenght range from 350 to 750 nm as a function of oxygen pressure. They slow a broad structureless continuum similar to a black-body radiator. Using the emissivity of a small spherical particle and Planck's law the experimental spectra can be reproduced and temperatures (up to 3200 K) can be extracted. To demonstrate that the heating process does not influence the spectra, they are compared to spectra obtained after multiphoton absorption.