Non-dissociative laser induced desorption of molecules from dielectric surfaces

Abstract

We have been concerned with the non-dissociative desorption of 1,3-cyclohexadiene, pyridine, 2-piccoline, N-methyl-aniline and methyl-pyrazine adsorbed on surfaces of LiF (100), MgF 2, quartz and surfaces coated with Ar, Xe and N 2. As an example we present our results on the non-dissociative desorption of methyl-pyrazine from quartz. We used tunable UV laser light (248–280 nm) to excite the π→π ∗ electronic transition centered at 266 nm. The dependence of the desorption cross sections on layer thickness, laser fluence and laser wavelength has been obtained by quantitative analysis of the TOP (time of flight) mass spectra of the desorbing molecules. Two different desorption channels have been found with quantum yields two orders of magnitude different from each others. A non-thermal channel has a quantum yield of 10 −4–10 −5 at 266 nm. The second channel occurs at thicker layers and higher laser fluences with quantum yields⩾10 −3. The desorption signal is proportional to the absorption coefficient.