Giuseppe Del Re

Vibronic coupling in electronic transitions with significant Duschinsky effect

Conceptual and mathematical difficulties arise in the study of transitions between vibronic states belonging to crossing Born-Oppenheimer hypersurfaces with significantly different positions and shapes of the minimum-energy nuclear configurations (Duschinsky effect). This article presents an analytic procedure for the evaluation of the pertinent coupling integrals, adopting a normal coordinate reference system for the internal nuclear motion and harmonic approximation. The Duschinsky effect is properly considered. The procedure was applied to the dynamics of electron transfer in neutral mixed valence monoradicals, using the diabatic representation.

On the geometry of 3-amino-sydnones

Abstract The X-ray structure of molsidomine (3-morpholine-sydnoneimine) reveals a widening of the CNC angle of morpholine substituted at the N 3 atom of the sydnone moiety. This might be due to lone-pair delocalization, since sydnone is a mesoionic aromatic heterocycle, and its N 3 nitrogen atom is expected to undergo an important π -electron loss. With a view to clarifying this problem, the results of an extensive analysis of the literature and theoretical computations carried out with standard empirical and ab initio methods have been discussed with the help of the IML-EH method, a version of the EHT method which includes hybridization, α localization and mutual charge adjustment. Although the computational results can be interpreted as favouring the prediction that N 3 of sydnones is π -electron deficient, no significant delocalization of the lone pair of the amine substituent is predicted. The CNC angle widening appears to be due to hybridization–polarization effects. In the course of the paper, numerical information relevant to further research on the sydnones and on the N–N bond is presented and discussed.