IR SPECTROSCOPY OF SIZE-SELECTED CLUSTERS AT 3-MU-M WAVELENGTH

An IR injection-seeded optical parametric oscillator (OPO) with narrow bandwidth (Gamma less than or equal to 0.25 cm(-1)) and high energy (E greater than or equal to 4 mJ/pulse) output between 2.5 and 4 mu m has been developed for cluster spectroscopy in molecular beams. The oscillator contains a LiNbO3 crystal is pumped by the 1,064 mu m fundamental of a Q-switched Nd:YAG laser. The IR seed radiation is obtained by difference frequency mixing the output of a tunable dye laser with the second harmonic of the same Nd:YAG laser in a LiIO3 crystal. After characterization, the OPO has been used to measure absorption spectra of small hydrogen-bonded clusters (HF)(n) and (H2O)(n) where n ranges for 2 to 8. The various spectral features could be assigned to specific cluster sizes by dispersing the cluster beam with a secondary rare gas beam and by measuring the laser-induced depletion as a function of the scattering angle.