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Figure 2. Ion/surface collision spectrum recorded after collision of 30 eV benzene molecular ions at an H-SAM surface. The ion at m/z 91 corresponds to the addition of a methyl group followed by loss of H 2 and that at m/z 65 to further loss of C 2 H 2 . The peak at m/z 79 is due to a H atom abstraction reaction. The inset shows the collision process and some reaction products. Reprinted from ref 72.

The diffusion of molecules in amorphous water and methanol films has been investigated on the basis of time-of-flight secondary ion mass spectrometry as a function of temperature. The glass-liquid transition of the amorphous water film occurs at 130-145 K as confirmed from the surface segregation of embedded methanol molecules. The morphology of the pure amorphous water film changes drastically at 160 K as a consequence of dewetting induced by the surface tension and the strongly decreased viscosity of the film. The morphology of the amorphous methanol film changes at 115 K following the self-diffusion onset at 80 K. The binary films of water and heavy methanol are intermixed completely at 136 K as evidenced by the occurrence of the H/D exchange.

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