High resolution and high sensitivity laser spectroscopy of small moleculesand clusters

With sensitive techniques, such as phase-modulation diode laser spectroscop y, opto-acoustic and opto-thermal spectroscopy, overtone spectra of small m olecules are recorded which allow the specific detection of pollutant molec ular gases and investigations of intramolecular vibrational energy transfer . Examples of molecules studied so far are H2S, CS2, C2H2, OCS, CHCl3 and C 2H4. With resonant two-photon two color ionization spectroscopy, isotope-se lective detection of small metal clusters in cold molecular beams has been achieved with sub-Doppler spectral resolution. Some of these techniques and spectroscopic results are discussed in the present paper.