MATRIX-GUEST ENERGY-TRANSFER IN MATRIX-ASSISTED LASER-DESORPTION

Molecular dynamics was used to analzye energy transfer rates between m atrix and guest molecules in matrix-assisted laser desorption allowing for a large number of internal degrees of freedom. The effect of init ial matrix temperature jump on internal energy equilibration times and on guest limiting temperatures has been studied on a model system com prising a pyridine-3-carboxylic acid matrix and leucine enkephalin (Ty r-Gly-Gly-Phe-Leu) guest molecule, It appears that the energy transfer rates between matrix and guest molecules depend on the initial matrix temperature jump. The initial matrix temperature of 900 K leads to in complete desorption, whereas at 1500 K complete desorption and the for mation of an energy-transfer bottleneck was observed, Following the gu est center-of-mass at different initial matrix temperatures indicates that in the case of 1500 K and 3000 K the desorption process is comple te, whereas at 900 K the guest molecule stays near the matrix surface, In the case of complete desorption deeper embedding of the guest mole cules leads to somewhat lower guest limiting temperatures, Uniformly h igher limiting temperatures are observed for higher laser irradiance a nd the increase in burial depth leads to more complete equilibration b etween the two species. (C) 1997 by John Wiley & Sons, Ltd.