Nonadiabatic wave packet dynamics of NO2 on the X̃ 2A′/Ã 2A′ conical intersection

Abstract

The NO2 optical spectrum and wave packet dynamics are deeply influenced by the conical intersection between the first two adiabatic potentials X̃ 2A′ and à 2A′ and by the (ν1,ν2) Fermi resonance of the upper electronic state 2B2. By considering a Franck–Condon excitation, we have expanded the NO2 wave packet in the basis of the nonadiabatic eigenstates and have studied the quantum dynamics on the coupled potentials. We have calculated the time evolution of the survival probability of different initial packets, of the populations of the diabatic and adiabatic electronic states and of the vibrational ones, of the energy distribution among the various degrees of freedom, of the average position, and of the probability density. The packet is mainly created on the upper diabatic or adiabatic potential, jumps three times between the adiabatic states up to about 58 fs, whose populations oscillate with a period close to that of the 2B2 bending mode, but it passes almost monotonically to the ground diabatic state, where it mainly moves for t>83 fs. During the time evolution, the energy is transformed from potential to kinetic and from electronic to vibrational, and flows from the bending to the stretching modes. The packet moves along both the symmetric stretching and bending directions, without splitting along the antisymmetric stretching, and the trajectory thus crosses the intersection seam four times. The dynamics becomes more and more complex and incoherent as time increases: no appreciable motion of the wave packet average position can be seen after 100 fs and all the available phase space is filled at about 200 fs, but the packet still feels the 2B2 Fermi resonance to about 350 fs.