Nonadiabatic wave packet dynamics of NO2 on the (X)over-tilde(2)A '/(A)over-tilde(2)A ' conical intersection

The NO2 optical spectrum and wave packet dynamics are deeply influenced by the conical intersection between the first two adiabatic potentials (X)over -tilde(2)A' and (A)over-tilde(2)A' and by the (nu(1), nu(2)) Fermi resonanc e of the upper electronic state B-2(2). By considering a Franck-Condon exci tation, we have expanded the NO2 wave packet in the basis of the nonadiabat ic eigenstates and have studied the quantum dynamics on the coupled potenti als. We have calculated the time evolution of the survival probability of d ifferent initial packets, of the populations of the diabatic and adiabatic electronic states and of the vibrational ones, of the energy distribution a mong the various degrees of freedom, of the average position, and of the pr obability density. The packet is mainly created on the upper diabatic or ad iabatic potential, jumps three times between the adiabatic states up to abo ut 58 fs, whose populations oscillate with a period close to that of the B- 2(2) bending mode, but it passes almost monotonically to the ground diabati c state, where it mainly moves for t greater-than 83 fs. During the time ev olution, the energy is transformed from potential to kinetic and from elect ronic to vibrational, and flows from the bending to the stretching modes. T he packet moves along both the symmetric stretching and bending directions, without splitting along the antisymmetric stretching, and the trajectory t hus crosses the intersection seam four times. The dynamics becomes more and more complex and incoherent as time increases: no appreciable motion of th e wave packet average position can be seen after 100 fs and all the availab le phase space is filled at about 200 fs, but the packet still feels the B- 2(2) Fermi resonance to about 350 fs. (C) 1999 American Institute of Physic s. [S0021-9606(99)01606-2].