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The temperature dependent stepwise deprotonation of 5,10,15,20-tetra(p-hydroxyphenyl)porphyrin is investigated using photoelectron spectroscopy. An abundance of pyrrolic relative to iminic nitrogen and a decrease in the ratio of the amount of -NH- to -N= with increasing annealing temperature is found. In contrast to the molecules adsorbed on Au(111), on the more reactive Ag(110) surface, partial dissociation of the hydroxyl groups and subsequent diffusion and rebonding of hydrogen to the central nitrogen atoms resulting in a zwitterionic molecule was clearly observed. Moreover, partial C-H bond cleavage and the formation of new covalent bonds with adjacent molecules or the surface starts at a relatively high annealing temperature of 300{deg}C. This reaction is identified to occur at the carbon atoms of the pyrrole rings, which leads also to a shift in the N 1s signal and changes in the valence band of the molecules. Our results show that annealing can significantly alter the molecules which were deposited depending on the maximum temperature and the catalytic properties of the specific substrate. The thermal stability should be considered if a molecular monolayer is prepared from a multilayer by desorption, or if annealing is applied to enhance the self-assembly of molecular structures.
This review article discusses advances in the use of time-resolved photoelectron spectroscopy for the study of non-adiabatic processes in molecules. A theoretical treatment of the experiments is presented together with a number of experimental examples.
We report the observation of quantized translational and rotational motion of molecular hydrogen inside the cages of C60. Narrow infrared absorption lines at the temperature of 6K correspond to vibrational excitations in combination with translationa
A major goal of many spectroscopic techniques is to provide comprehensive information on the local chemical environment. Electron transfer mediated decay (ETMD) is a sensitive probe of the environment since it is actively involved in this non-local r
The study of the formation of molecular hydrogen on low temperature surfaces is of interest both because it allows to explore elementary steps in the heterogeneous catalysis of a simple molecule and because of the applications in astrochemistry. Here
Here, we report the observation of electron transfer mediated decay (ETMD) involving Mg clusters embedded in helium nanodroplets which is initiated by the ionization of helium followed by removal of two electrons from the Mg clusters of which one is