Investigation about of molecular dynamics has been of interest in both computational and experimental research areas [1]. Recently, dynamic phenomena such as rotations [2] and tautomerism [3] have been the subject of theoretical researches. In this line, potential energy surfaces (PESs) for dynamic motion have been studied by both computational and experimental methods[4]. A simple potential energy surface can provide an adequate description of chemical systems. PES levels can be crossed in diabatic levels by spin-orbit couplings and a breakdown in the BOA can lead to a transition between adiabatic potentials in a dynamic system at the crossing point. The possibility of diabatic level crossing was studied first by Landau and Zener[5].

In continuation of our previous researches about tautomerism and in order to investigate the possibility of diabatic crossing in PESs by theoretical methods, 2-(pyridin-2-yl) furan-3-ol (PYFO) were designed. This molecule has three interesting intra-molecular motions (below figure), Bond rotation (br), ring rotation (rr) and tautomerism.