Abstract
The desorption of intact molecules by pulsed IR irradiation is shown to depend on the IR absorption of the matrix. IR transparent matrices, such as NaCl or NH4NO3, increase the total yield and the shot-to-shot stability of the sample. IR absorbing matrices decrease the yield of intact molecules and increase the amount of pyrolysis products. Using semi-transparent sugar matrices with dipeptide samples, the most intense fragment, i.e. the parent molecule having lost 18 u, is suppressed. This fragment is formed by pyrolysis during IR desorption. Three other prominent fragments are caused by the UV photoionization step. The experimental results suggest that a model involving bulk stresses and strain may be necessary to explain the observations.
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