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Ab initio studies of two pyrimidine derivatives as possible photo-switch systems

100%
Csehi A., Woywod C., Halász G., Vibók Á.
Open Physics
|
2013
|
vol. 11
|
issue 9
1141-1148
EN
The six lowest lying electronic singlet states of 8-(pyrimidine-2-yl)quinolin-ol and 2-(4-nitropyrimidine-2-yl)ethenol have been studied theoretically using the complete active space self-consistent-field (CASSCF) and M’ller-Plesset second-order perturbation theory (MP2) methods. Both molecules can be viewed as consisting of a frame and a crane component. As a possible mechanism for the excited-state relaxation process an intramolecular hydrogen transfer promoted by twisting around the covalent bond connecting the molecular frame and crane moieties has been considered. Based on this idea we have attempted to derive abstracted photochemical pathways for both systems. Geometry optimizations for the construction of hypothetical reaction coordinates have been performed at the MP2 level of theory while the CASSCF approach has been employed for the calculation of vertical excitation energies along the pathways. The results of the calculations along the specific twisting displacements investigated in this study do not support the notion of substantial twisting activity upon excitation of any of the five excited states at the planar terminal structures of the torsion coordinates of both molecules. However, the present analysis should be considered only as a first, preliminary step towards an understanding of the photochemistry of the two candidate compounds. For example, we have not performed any excited state geometry optimizations so far and the estimates of vertical excitation energies do not take dynamical electron correlation into account. Further work on this subject is in progress.
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Non-adiabatic interactions in charge transfer collisions

88%
Bacchus-Montabonel M.-C., Rozsályi E., Bene E., Halász G., Vibók Á.
Open Physics
|
2013
|
vol. 11
|
issue 9
1149-1156
EN
An analysis of the charge transfer mechanism in the collision of multiply charged ions with molecular and biomolecular targets is performed, considering the non-adiabatic interactions between the molecular states involved. Collisions of doubly charged C 2+ ions on small molecular targets, CO and OH, have been investigated, together with the analysis of charge transfer between C 4+ ions on uracil and halouracil biomolecular targets. The process is studied theoretically by means of ab-initio molecular calculations followed by a semi-classical treatment of the collision dynamics. The influence of rotational couplings is discussed with regard to the collision energy. Strong anisotropic and vibration effects are pointed out.
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