Description of molecular dynamics in intense laser fields by the time-dependent adiabatic state approach: Application to simultaneous two-bond dissociation of CO₂ and its control

We theoretically investigated the dynamics of structural deformations of CO₂ and its cations in near-infrared intense laser fields (∼10¹⁵ W cm^-2) by using the time-dependent adiabatic state approach. To obtain "field-following" adiabatic potentials for nuclear dynamics, the electronic Hamiltonian including the interaction with the instantaneous laser electric field is diagonalized by the multiconfiguration self-consistent-field molecular orbital method. In the CO₂ and CO₂⁺ stages, ionization occurs before the field intensity becomes high enough to deform the molecule. In the CO₂²⁺ stage, simultaneous symmetric two-bond stretching occurs as well as one-bond stretching. Two-bond stretching is induced by an intense field in the lowest time-dependent adiabatic state |1〉 of CO₂²⁺, and this two-bond stretching is followed by the occurrence of a large-amplitude bending motion mainly in the second-lowest adiabatic state |2〉 nonadiabatically created at large internuclear distances by the field from |1〉. It is concluded that the experimentally observed stretched and bent structure of CO₂³⁺ just before Coulomb explosions originates from the structural deformation of CO₂²⁺. We also show in this report that the concept of "xoptical-cycle-averaged potential" is useful for designing schemes to control molecular (reaction) dynamics, such as dissociation dynamics of CO₂, in intense fields. The present approach is simple but has wide applicability for analysis and prediction of electronic and nuclear dynamics of polyatomic molecules in intense laser fields.