Diatomic molecule, nonadiabatic transition

Summary. An effective scheme for the laser control of wavepacket dynamics applicable to systems with many degrees of freedom is discussed. It is demonstrated that specially designed quadratically chirped pulses can be used to achieve fast and near-complete excitation of the wavepacket without significantly distorting its shape. The parameters of the laser pulse can be estimated analytically from the Zhu-Nakamura (ZN) theory of nonadiabatic transitions. The scheme is applicable to various processes, such as simple electronic excitations, pump-dumps, and selective bond-breaking, and, taking diatomic and triatomic molecules as examples, it is actually shown to work well. 

Strongly nonadiabatic behaviour is often localized where the actual character of systems changes drastically. So, when the interaction between two atoms is considered as a function of the internuclear distance R, it is found that the transition between the typical behaviour of separated atoms and that of a diatomic molecule is often localized around sharp maxima in the elements of a P(R) matrix [s]. 

In his early study of nonadiabatic transitions of a diatomic molecule due to the Coriolis coupling, H. Nakamura proposed a new electronic Hamiltonian [290], in which a part of the rotational interactions is explicitly taken into account as... 

Note that <[)/ are electronic wavefunctions that are not eigenfunctions of H. In every realistic case (except in diatomic molecules) where the sum over states J is truncated, the derivative coupling cannot vanish completely for every but it can become negligibly small. Making f/y very small corresponds to choosing the electronic wavefunctions so that they are always smooth functions of the nuclear coordinates. Physically diabatic functions maintain the character of the states. For example, assume that a diabatic state <[)] corresponds to a covalent configuration and another diabatic state 2 corresponds to an ionic configuration. Before a nonadiabatic transition occurs, the adiabatic states will be the same, v /i = tj)/ and v(72 = 2. After a nonadiabatic... 

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