No abstract

Photoelectron spectra obtained from ͑CsX) 3 Cs Ϫ (XϭCl,Br,I͒ cluster anions are strongly dependent on the temperature of the laser vaporization source in which they were produced. Spectral features that were present in clusters emerging from the source at room temperature disappear when the source is cooled to low temperature. This effect is consistent with spontaneous thermal isomerization in the isolated clusters, a precursor to the melting transition in bulk materials.