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. Optica l emission spectra have been recorded in the wavelength range from 350 to 750 nm as a function of oxygen pressure. They show a broad structu reless continuum similar to a black-body radiator. Using the emissivit y of a small spherical particle and Planck's law the experimental spec tra can be reproduced and temperatures (up to 3200 K) can be extracted . To demonstrate that the heating process does not influence the spect ra, they are compared to spectra obtained after multiphoton absorption .