VELOCITY DISTRIBUTIONS OF ANALYTE MOLECULES IN MATRIX-ASSISTED LASER-DESORPTION FROM COMPUTER-SIMULATIONS

The mass dependence of the velocity distributions of analyte molecules in matrix-assisted laser desorption is analyzed based on the results of molecular dynamics simulations. The spread of the velocities along the direction of the flow is found to be independent of the mass of th e analyte molecules and to reflect the entrainment of the analyte mole cules in the expanding matrix. The radial velocity distributions for b oth matrix molecules and analyte molecules of different masses, on the other hand, fit well to a Maxwell-Boltzmann distribution with the sam e temperature, suggesting the association of the spread in the radial velocities with the thermal motion in the plume. A consistent analytic al description of the complete velocity distribution for matrix molecu les and analyte molecules of different masses is proposed based on the approximation of a range of stream velocities and a single temperatur e in the ejected plume. (C) 1998 John Wiley & Sons, Ltd.