Beyond the Born-Oppenheimer approximation : dynamics on several coupled potential energy surfaces (NO2, ...)
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Plot, according to our effective Hamiltonian adjusted against experimental data, of the two lowest adiabatic electronic surfaces of NO2 in the region of the conical intersection. q2 and q3 denote the bending and antisymmetric stretch normal coordinates.

Puce The Born-Oppenheimer separation of electronic and nuclear motions is a widely used approximation in molecular physics. Nonetheless, transitions between different electronic surfaces (non Born-Oppenheimer or non-adiabatic dynamics) represent a field of growing interest, because they appear to govern a large variety of fundamental processes, such as internal conversion, intersystem crossing, electron transfer and photoinduced reactions. Compared to Born-Oppenheimer dynamics, the study of non-adiabatic systems is made somewhat more complex by the fact that the Hamiltonian is a matrix instead of a scalar. For example, a 2x2 matrix is needed to describe two coupled electronic surfaces : the diagonal elements of the matrix are the Hamiltonians of the uncoupled electronic surfaces, while the off-diagonal terms account for the coupling between the two surfaces.

In this context, the conical intersection between the two lowest electronic surfaces of NO2, which takes place at about 10000 cm-1 above the quantum mechanical ground state (see figure below), has already attracted much attention from both the experimental and theoretical points of view. In particular, most of the experimental spectra were recorded in our University, in the group of R. Jost. My work in this field was precisely motivated by the need for a model, which would satisfactorily reproduce the experimental vibronic spectrum of NO2 up to and above the region of the conical intersection.

For this purpose, we first derived a Canonical Perturbation procedure for non-adiabatic systems, which provided us with a good insight into the non Born-Oppenheimer coupling mechanism. Based on the conclusions of this study, we then proposed an efficient method for calculating the eigenstates and adjusting the parameters of an effective Hamiltonian in good agreement with the experimental spectrum.

We are now studying the non-adiabatic dynamics of NO2 on the basis of this effective model.

Puce Related articles (suggested ones in red) :
56 -
Slow periodic oscillations in time domain dynamics of NO2
M. Sanrey and M. Joyeux,
J. Chem. Phys. 126 (2007) 074301 (1-8)
[full text]
        copyright : The American Institute of Physics ([Abstract])
55 -
Quantum mechanical and quasiclassical investigation of the time domain nonadiabatic dynamics of NO2 close to the bottom of the X2A1-A2B2 conical intersection

M. Sanrey and M. Joyeux, J. Chem. Phys. 125 (2006) 014304 (1-8)

[full text]        copyright : The American Institute of Physics ([Abstract])
40 -
An effective model for the X2A1-A2B2 conical intersection in NO2
M. Joyeux, R. Jost and M. Lombardi, J. Chem. Phys. 119 (2003) 5923-5932
[full text]        copyright : The American Institute of Physics ([Abstract])
38 -
Canonical perturbation theory for highly excited dynamics
M. Joyeux and D. Sugny, Can. J. Phys. 80 (2002) 1459-1480 (tutorial article)
[full text]          copyright : NRC Research Press ([Abstract])
37 -
The X2A1-A2B2 conical intersection in NO2 : determination of the coupling parameter lambda from high resolution experimental data
R. Jost, M. Joyeux and M. Jacon, Chem. Phys. 283 (2002) 17-28
[Abstract]          [Ask for an electronic reprint by email]
35 -

A local diabatic representation of non-Born-Oppenheimer dynamics
M. Joyeux, D. Sugny and M. Lombardi, Chem. Phys. Lett. 352 (2002) 99-105
[Abstract]          [Ask for an electronic reprint by email]

34 -
A new canonical perturbation procedure for studying nonadiabatic dynamics
D. Sugny and M. Joyeux, Chem. Phys. Lett. 337 (2001) 319-326
[Abstract]          [Ask for an electronic reprint by email]