Time-of-flight study of the ionic and neutral particles produced by pulsed-laser ablation of frozen glycerol

The emitted particles from pulsed-laser ablation (PLA), lambda =193 nm and fluence=88-400 mJ/cm(2), of frozen glycerol was examined using time-of-flight mass spectrometry. The data are analyzed using supersonic molecular-beam theory and the result is interpreted using a thermal/fluid-dynamic model. Both intact and fragmented glycerol are emitted in the PLA process at all fluences and their concentration ratio is fluence dependent. Fragmentation occurs predominantly at one of the C-C bonds forming CH2-OH (31 amu) and HO-CH2-CH-OH (61 amu). CH3 is produced at the target which requires the protonation of a CH2 fragment. At fluences higher than 250 mJ/cm(2), ions are detected. These ions have very high velocity, > 2000 m/s, and their intensity increases with fluences. PLA is thus not suitable for glycerol transfer under these conditions due to fragmentation. The data show that particle emission proceeds as a simple thermal vaporization process at fluences < 200 mJ/cm(2). Higher fluences will yield a Knudsen layer (KL), which is formed in front of the target surface. For fluences > 300 mJ/cm(2), particles from the KL go through unsteady adiabatic expansion prior to free flight. Models of particle and ion formation and interaction are proposed and discussed. (C) 2001 American Institute of Physics.