Diabatic crossings

The aim ofthe present study is double i) to show that BET can be used as a tool for analyzing the adiabatic PESs and localizing the diabatic crossings which govern the overall electron changes ii) to provide a topological description of the three-electron bonds. 

The main result of these first detailed experimental studies of the AI mechanism is that, even at thermal velocity, the system R -H follows a potential curve F ( R) that diabatically crosses an infinite number of potential curves dissociating into R+H, H being hydrogen in a Rydberg state, and continues to be well defined in the ionization continuum. We might mention that results on AI are also interesting because AI is the reverse reaction to the important process of dissociative recombination of molecular ions. 

The TOF spectrum of the Cl or Br atom is measured as a function of wavelength, with the polarization of the laser selected so that only TTq is excited. The peaks that are observed in the spectrum can be identified with atoms in either the 3/2 Dr pl/2 state> so that the experimental data can be used to determine the probability, P, for the diabatic crossing. The Landau-Zener formula for this probability is given by... 

Predissociation effects may be treated in either the diabatic (crossing potential curves) or adiabatic (noncrossing curves) representation. Criteria for choosing the more convenient representation are discussed in Section 3.3.4. When the adiabatic representation is appropriate, predissociative interactions between states of the same symmetry result from the nuclear kinetic energy operator. The matrix elements of this operator cannot be factored in the same way as Eq. (7.5.14) because the electronic element... 

The most fundamental quantum mechanical model of curve crossing is the linear potential model (in coordinate R), in which the diabatic crossing potentials V R) and V2(R) are linear functions of R and the diabatic coupling V(R) is constant (=A). The basic coupled Schrodinger equations are (29)... 

V and Af are the classical velocity and the difference of slopes of the diabatic potentials at the diabatic crossing point Rq. /r(Ro) is the electronic transition moment at the diabatic crossing point and q the electric field amplitude of the laser field. 

The diabatic surface crossing provides information about the origin of a critical point and its geometry, which is related to the position along the reaction coordinate r,where the diabatic surface crossing occurs. The diabatic cross-sections for the three reactions is shown in Fig. 7. ... 

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