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
ABSTRACT We theoretically investigated the dynamics of structural deformations of CO(2) and its cations in near-infrared intense laser fields (approximately 10(15) 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 CO(2) and CO(2+) stages, ionization occurs before the field intensity becomes high enough to deform the molecule. In the CO(2)(2+) 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 CO(2)(2+), 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 CO(2)(3+) just before Coulomb explosions originates from the structural deformation of CO(2)(2+). We also show in this report that the concept of "optical-cycle-averaged potential" is useful for designing schemes to control molecular (reaction) dynamics, such as dissociation dynamics of CO(2), 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.
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ABSTRACT: A ground state wave function of a one-dimensional H2 molecule is derived numerically by the extended multi-configuration time-dependent Hartree-Fock (MCTDHF) method. The electronic orbitals and the amplitudes for the nuclear motion constituting the ground-state wave function are derived by solving the coupled equations of motion by the imaginary time propagation. Comparisons with the results obtained by the Born-Huang (BH) expansion method as well as with the exact wave function reveal that the memory size required in the extended MCTDHF method is about two orders of magnitude smaller than in the BH expansion method.Chemical Physics Letters 03/2014; 595. DOI:10.1016/j.cplett.2014.01.055 · 1.99 Impact Factor
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ABSTRACT: We study the break up of OCS in intense femtosecond laser radiation using the FEMPULS technique to vary the laser pulse duration from 7fs to 200fs. Newton and Dalitz plots show the progression of molecular deformation and break up for OCS3+ and OCS4+. For increasing pulse length, the concerted three body dissociation exhibits increasing bending, and the amount of stepwise dissociation decreases. For the longest pulses however the stepwise process increases again. Both phenomena can be interpreted in terms of the effect of the laser field on lower charge states and the behaviour of a wave packet on a saddle point potential. The experiment illustrates the ability of the Coulomb imaging method to track molecular geometry and dynamics and indicates a new path to laser control of molecular parameters.Journal of Electron Spectroscopy and Related Phenomena 08/2014; 195. DOI:10.1016/j.elspec.2014.05.003 · 1.55 Impact Factor
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ABSTRACT: Mode-selective chemistry has been a dream of chemists since the advent of the laser in the 1970s. Despite intense effort, this goal has remained elusive due to efficient energy randomization in polyatomic molecules. Using ab initio molecular dynamics calculations, we show that the interaction of molecules with intense, ultrashort mid-infrared laser pulses can accelerate and promote reactions that are energetically and entropically disfavored, owing to efficient kinetic energy pumping into the corresponding vibrational mode(s) by the laser field. In a test case of formyl chloride ion photodissociation, the reactions are ultimately complete under field-free conditions within 500 fs after the laser pulse, which effectively overcomes competition from intramolecular vibrational energy redistribution (IVR). The approach is quite general and experimentally accessible using currently available technology.Journal of Physical Chemistry Letters 08/2012; 3(18):2541–2547. DOI:10.1021/jz301038b · 6.69 Impact Factor