LASER DESORPTION VACUUM ULTRAVIOLET PHOTOIONIZATION OF ALKANETHIOLATESELF-ASSEMBLED MONOLAYERS/

Self assembled monolayers of straight-chain alkanethiolates (RS) on go ld were studied by nitrogen laser desorption followed by vacuum ultrav iolet (118 nm) photoionization of secondary neutrals in a time-of-flig ht mass spectrometer. The dominant feature of all photoionization mass spectra were the dimers (RSSR+) for all thiolates studied. No monomer ions (RS') were observed, in contrast with previous results from time -of-flight secondary ion and direct laser desorption mass spectrometry . Results are presented from experiments on the tetradecyl (C-14) and hexadecyl (C-16) mercaptan monolayers. Mixed C-14/C-16 monolayers gene rated both pure and mixed dimers, indicating a facile association betw een different monomer chain lengths. (C) 1997 by John Whey & Sons, Ltd .