Laser Spectroscopy of Molecules and Clusters

Abstract

The advantages of collimated cold supersonic beams for sub-Doppler laser spectroscopy of molecules and small clusters are discussed and illustrated by several examples. These include sub-Doppler spectroscopy of the SO2 molecule in the ultraviolet and of NO2 in the visible region. Lifetime measurements under collision-free conditions, stepwise excitation of high lying molecular Rydberg states, and sub-Doppler double resonance spectroscopy of Na3 demonstrate the achievements possible by combining molecular beam techniques with various methods of laser spectroscopy. The relevance of the experimental results for our understanding of the dynamics of molecules in excited states and for the development of new theoretical approaches is emphasized. Some sensitive detection techniques are presented which are in particular useful when cw lasers are used for spectroscopy in cw molecular beams at low densities.