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Energy Selection in Nonadiabatic Transitions.

Giovanni Granucci1, Giacomo Melani1, Maurizio Persico1

  • 1Dipartimento di Chimica e Chimica Industriale, Università di Pisa , via Moruzzi 13, I-56124 Pisa, Italy.

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Molecules in nonadiabatic transitions show distinct energy distributions in populated electronic states. This energy selection effect, observable in photodissociation, is pronounced for broad wavepacket energy spectra.

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Area of Science:

  • Quantum Chemistry
  • Molecular Dynamics
  • Spectroscopy

Background:

  • Nonadiabatic transitions are crucial in molecular processes like photodissociation.
  • Understanding energy distribution in electronic states is key to controlling molecular reactions.

Purpose of the Study:

  • Investigate energy mean values and distributions in electronic states during nonadiabatic transitions.
  • Analyze the energy selection effect in different molecular models.

Main Methods:

  • Analysis of three models: two limiting cases (adiabatic and diabatic) and one realistic photodissociation model.
  • Application of first-order perturbation theory for models I and II.
  • Numerical treatment for model III.

Main Results:

  • Consistent evidence of an energy selection effect across all models.
  • Wavepacket components undergoing transitions exhibit higher mean energy.
  • Quantum mechanical derivation of the Landau-Zener rule from model II.

Conclusions:

  • The energy selection effect is a general phenomenon in nonadiabatic transitions.
  • Experimental observation is feasible in diatomic molecule photodissociation.
  • The effect is significant for wavepackets with broad energy spectra, especially from ultrashort pulse excitation.