IS LASER-HEATING ADVANTAGEOUS FOR THERMAL-DESORPTION OF LARGE POLAR-MOLECULES

A systematic study on the desorption and dissociation kinetics of ethy lene glycol and poly(ethylene glycol) oligomers (PEG) with masses rang ing from 62 to 35 000 Da from a silica surface was undertaken. The mea surements include characterization of the PEG-silica adsorption system using temperature programmed desorption, investigation of the surface coverage, and chemical composition during slow surface heating by rea l time x-ray photoelectron spectroscopy, and determination of translat ional energy distributions following nanosecond CO2 laser desorption. We found that even for heating rates exceeding 10(9) K/s desorption ca n be described by a thermal model. Intact desorption was limited to PE Gs with masses less than or equal to 1000 Da for classical as well as for laser heating. (C) 1997 American Institute of Physics.