DIRECT MEASUREMENT OF WATER CLUSTER CONCENTRATIONS BY INFRARED CAVITYRINGDOWN LASER-ABSORPTION SPECTROSCOPY

The recently developed technique of infrared cavity ringdown laser abs orption spectroscopy (IR-CRLAS) has been employed in the 3.0 mu m regi on to determine the absolute concentrations of water dimers, trimers, tetramers, and pentamers in a pulsed supersonic expansion for the firs t time. Additional spectral features are reported, one of which we ass ign to the bound O-H stretching bands of the hexamer. Additionally, by simple variation of the jet stagnation pressure, the collective O-H s tretching absorption from all clusters produced in the expansion was o bserved to change from that of discrete features of small clusters to band profiles of liquid water and finally to amorphous ice.