SUBLIMATION VERSUS FRAGMENTATION IN MATRIX-ASSISTED LASER DESORPTION

A kinematic model for the laser-induced introduction into the gas phase of large molecules embedded in a host matrix is discussed. The desorption of undegraded large molecules is argued to be a kinetic effect due to potentially rapid destruction of the host matrix. The two separate mechanisms are considered, sublimation and fragmentation of the matrix. Due to the choice of hosts, sublimation is more typical of experiments using UV laser pulses. In general, sublimation is found to be more efficient because it can turn itself off. The matrix destruction competes with host-guest vibrational energy transfer. The energy content of the guest can be reduced by working at low volume concentrations, special choice of host matrices and using an initially cold sample. © 1990.