Alexey D. Kondorskiy

Strong field effects occurring during the interaction of femtosecond laser pulses with “bowtie” composite nanoantennas are numerically simulated. The effect of the nanoantenna shape and laser pulse parameters on the “plateau” formation in the photoelectron energy spectra is studied. It is shown that the upper boundary of the “plateau” can increase appreciably for the same laser pulse parameters when nanoantenna element sizes are different. Physical explanation of the phenomenon is given.

We present an approach, which allows to employ the adiabatic wave packet propagation technique and semiclassical theory to treat the nonadiabatic processes by using trajectory hopping. The approach developed generates a bunch of hopping trajectories and gives all additional information to incorporate the effect of nonadiabatic coupling into the wave packet dynamics. This provides an interface between a general adiabatic frozen Gaussian wave packet propagation method and the trajectory surface hopping technique. The basic idea suggested in [A. D. Kondorskiy and H. Nakamura, J. Chem. Phys. 120, 8937 (2004)] is revisited and complemented in the present work by the elaboration of efficient numerical algorithms. We combine our approach with the adiabatic Herman-Kluk frozen Gaussian approximation. The efficiency and accuracy of the resulting method is demonstrated by applying it to popular benchmark model systems including three Tully’s models and 24D model of pyrazine. It is shown that photoabsorption spectrum is successfully reproduced by using a few hundreds of trajectories. We employ the compact finite difference Hessian update scheme to consider feasibility of the ab initio “on-the-fly” simulations. It is found that this technique allows us to obtain the reliable final results using several Hessian matrix calculations per trajectory.

Ultraviolet absorption cross sections of the main and substituted sulfur monoxide (SO) isotopologues were calculated using R-Matrix expansion technique. Energies, transition dipole moments, and nonadiabatic coupling matrix elements were calculated at MRCI/AV6Z level. The calculated absorption cross section of ³²S¹⁶O was compared with experimental spectrum; the spectral feature and the absolute value of photoabsorption cross sections are in good agreement. Our calculation predicts a long lived photoexcited SO* species which causes large non-mass dependent isotopic effects depending on the excitation energy in the ultraviolet region.

Numerical calculations are performed and spectral characteristics and spatial field distributions are studied upon excitation of a chain of two and three nanoparticles by a near-field optical microscope probe. It was found that there is a set of frequencies near the absorption line of nanoparticle material, at which the electromagnetic field can most efficiently propagate along the chain. It is shown that the efficiency of the electromagnetic energy transfer due to the quadrupole interaction between particles can exceed the efficiency of the transfer caused by the dipole interaction.

On-the-fly nonadiabatic ab initio molecular dynamics simulations have been carried out for three anionic species of indolylmaleimides (3-(1H-3-indolyl)-2,5-dihydro-1H-2,5-pyrroledione, IM) to clarify the mechanisms of photochemical reactions. The results are obtained for (i) a monovalent anion with a deprotonated indole NH group (IM⁻′), (ii) a monovalent anion with a deprotonated maleimide NH group (IM⁻′′) and (iii) a divalent anion with doubly deprotonated indole and the maleimide NH groups (IM²⁻). Quantum chemical calculations are treated at the three state averaged complete-active space self-consistent field level for 6 electrons in 5 orbitals with the cc-pVDZ basis set (CAS (6, 5) SCF/cc-pVDZ). Molecular dynamics simulations are performed with electronically nonadiabatic transitions included using the Zhu–Nakamura version of the trajectory surface hopping (ZN-TSH) method. It is found that the nonadiabatic transitions occur accompanied by the stretching and shrinking motions of the N(7)–C(8) bond in the case of IM⁻′ and the C(11)–N(12) bond in IM²⁻ rather than the twisting motion of the dihedral angle. We also found that the ultrafast S₂ → S₁ nonadiabatic transitions occur through the conical intersection (CoIn) right after photoexcitation to S₂ in IM⁻′ and IM²⁻. Furthermore, the S₁ → S₀ nonadiabatic transitions are found to take place in IM⁻′. It is concluded that IM²⁻ would mainly contribute to the photoemission, because the S₁ ← S₀ and S₂ ← S₀ transitions of IM⁻′′ are dipole-forbidden transitions and, moreover, IM²⁻ is found to be the only species to stay in the S₁ state without non-radiative decay.

Theoretical ideas are proposed for laser control of chemical dynamics. There are the following three elementary processes in chemical dynamics: (i) motion of the wave packet on a single adiabatic potential energy surface, (ii) excitation/de-excitation or pump/dump of wave packet, and (iii) nonadiabatic transitions at conical intersections of potential energy surfaces. A variety of chemical dynamics can be controlled, if we can control these three elementary processes as we desire. For (i) we have formulated the semiclassical guided optimal control theory, which can be applied to multidimensional real systems. The quadratic or periodic frequency chirping method can achieve process (ii) with high efficiency close to 100%. Concerning process (iii) mentioned above, the directed momentum method, in which a predetermined momentum vector is given to the initial wave packet, makes it possible to enhance the desired transitions at conical intersections. In addition to these three processes, the intriguing phenomenon of complete reflection in the nonadiabatic-tunneling-type of potential curve crossing can also be used to control a certain class of chemical dynamics. The basic ideas and theoretical formulations are provided for the above-mentioned processes. To demonstrate the effectiveness of these controlling methods, numerical examples are shown by taking the following processes: (a) vibrational photoisomerization of HCN, (b) selective and complete excitation of the fine structure levels of K and Cs atoms, (c) photoconversion of cyclohexadiene to hexatriene, and (d) photodissociation of OHCl to O + HCl.

Full-dimensional laser control of HCN-CNH isomerization is carried out to demonstrate the effectiveness of the recently formulated semiclassical guided optimal control theory. The algorithm is designed so that the controlling field does not exceed the predetermined limit of intensity to avoid the undesirable multiphoton inonization process. The controlling field is found to be rather simple and physical understanding of the controlling process becomes possible. It is demonstrated that the quantum-mechanical effects taken into account by the semiclassical treatment are essential for the control and that the purely classical treatment cannot be reliable. The theory is now applicable to any realistic molecular dynamics of many degrees of freedom.