Time-dependent multiconfiguration theory for electronic dynamics of molecules in intense laser fields: a description in terms of numerical orbital functions

The equations of motion (EOMs) for spin orbitals in the coordinate representation are derived within the framework of the time-dependent multiconfiguration theory developed for electronic dynamics of molecules in intense laser fields. We then tailor the EOMs for diatomic (or linear) molecules to apply the theory to the electronic dynamics of a hydrogen molecule in an intense, near-infrared laser field. Numerical results are presented to demonstrate that the time-dependent numerical multiconfiguration wave function is able to describe the correlated electron motions as well as the ionization processes of a molecule in intense laser fields.     

强激光场中NO分子多光子选择激发──含时薛定鄂方程的代数解法

报道了在半经典偶极近似下应用二次型非谐振子李代数模型研究强激光场中NO分子的多光子选择激发，并计算了NO分子的跃迁几率．     

Optimal control of ultrafast laser driven many-electron dynamics in a polyatomic molecule: N-methyl-6-quinolone

We report time-dependent configuration interaction singles calculations for the ultrafast laser driven many-electron dynamics in a polyatomic molecule, N-methyl-6-quinolone. We employ optimal control theory to achieve a nearly state-selective excitation from the S(0) to the S(1) state, on a time scale of a few ( approximately 6) femtoseconds. The optimal control scheme is shown to correct for effects opposing a state-selective transition, such as multiphoton transitions and other, nonlinear phenomena, which are induced by the ultrashort and intense laser fields. In contrast, simple two-level pi pulses are not effective in state-selective excitations when very short pulses are used. Also, the dependence of multiphoton and nonlinear effects on the number of states included in the dynamical simulations is investigated.     

臭氧分子在激光场中的多光子激发

采用二次量子化方法和酉变换讨论了O3分子在激光场中的多光子激发.推导出了O3分子的振动Hamiltonian 算子、从基态到各激发态的跃迁几率公式,以及O3分子从激光场中吸收的光子数公式,并分析了计算结果.这包括对O3分子伸缩振动能谱的计算及与实验结果的比较,跃迁几率随外场频率的变化、随时间的变化,以及O3分子在辐射场中的能量吸收情况(取光场强度为5×10-2 W/cm2).建立讨论所有具有C2v对称分子从基态到第四激发态以下各态多光子激发问题的模型.     

MULTIPHOTON EXCITATION OF A WATER MOLECULE IN INTENSE LASER FIELDS

A stretch vibration Hamiltonian of H_2O has been derived by using the second quantization, unitary transformations and the optimization of coefficients. The energy spectrum obtained from this Hamiltonian is in good agreement with that of experiments. The multiphoton excitation and the energy absorption of H_2O in intense laser fields have been calculated.     

分子转动和激光脉冲对多光子激发控制的影响(英文)

用解析代数方法研究了分子转动和激光脉冲对双原子分子多光子激发控制的影响并推导得到不同转动通道下的分子振动激发几率的解析表达式.为了考察转动能级和考虑分子转动后与激光场夹角的变化对分子多光子振动激发和振动激发控制的影响,我们计算并比较了分子纯振动和加入分子转动两种情况,并分别给出了分子与极化激光场在不同取向角下三光子选择激发的图像.研究发现分子的转动能级对多光子非共振激发有修正作用,但是分子转动会降低多光子激发的选择性,而选择合适的激光脉冲形状有利于目标多光子激发控制的实现.文中还进一步讨论了激光脉冲初相位对分子多光子激发控制的影响,发现脉冲初相位对多光子激发过程有明显的调制作用.     

Theory of laser-simulated surface processes

Theoretical techniques for describing laser-stimulated surface processes in a vacuum and at a gas-surface interface are presented. For adspecies-surface systems, the laser excitation of vibrational degrees of freedom is considered, and quantum-mechanical and classical models and also an “almost first-principles” treatment of the competition between multiphoton absorption and multiphonon relaxation are discussed. The laser excitation of electronic degrees of freedom is considered with respect to surface states of semiconductors and metals, for the predissociation of diatomic adspecies on metal substrates, for ionization, and for resonance fluorescence of a gaseous atom near a metal. In connection with gas-surface interactions, the influence of laser radiation on diffraction patterns and energy transfer in atom-surface scattering is explored. Collisional ionization and ion neutralization in the presence of laser radiation are discussed. The roles of partial pressure and surface coverage in laser-stimulated surface processes are analyzed. Finally, some ideas on surface waves and annealing are presented.     

Three‐peak Autler‐Townes splitting in the photoelectron spectrum of Li2 molecules caused by femtosecond laser pulses

Three‐peak Autler‐Townes (A‐T) splitting in the resonant multiphoton ionization photoelectron spectrum for a rotating Li₂ molecular system in femtosecond pulse laser fields is studied by using two‐dimension time‐dependent quantum wave packet method. The A‐T splitting results from rapid Rabi oscillation caused by intense femtosecond laser pulses. Because of the effects of molecular rotation and alignment, the Rabi oscillation in the population distribution will be damped in a certain degree. The three‐peak A‐T splitting can only be observed for a strongly aligned molecule with rapid Rabi oscillation. The three‐peak A‐T splitting dynamics can be affected by intensity, duration, temporal profile of laser pulse, and initial molecular rotational temperature. The conditions to observe the A‐T splitting are discussed in detail. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

HCl分子在激光场中的多光子激发

用二次量子化方法讨论了ＨＣｌ分子在激光场中的多光子激发，还包括对ＨＣｌ分子伸缩振动能级的计算，跃迁概率随外场频率的变化及随时间的变化（取光场强度１０~（－８）Ｗ／ｃｍ~２）。     

Laser-Induced Stabilization in Atomic and Molecular Systems

We present a short account of the recent progress in the study of a novel strong-field phenomenon recently uncovered: atoms and molecules may be stabilized by intense laser fields. The laser-induced atomic and molecular stabilization arises from quite different origins. We present a complex-scaling Fourier-grid Hamiltonian method for the discretization and solutior of the Schrödinger equation within the non-Hermitian Floquet Hamiltonian formalism. The method provides a simple, yet accurate and highly efficient, new technique for the determination of the complex quasienergies (E_RT ?Γ/2) of atoms and molecules. The real parts, E_RT provide the a.c. Stark shifts, and the imaginary parts, Γ, give rise to multiphoton ionization rates of atoms or multiphoton dissociation rates of molecules. The method is applied to the studies of (i) stabilization and ionization suppression of negative ions in high-frequency superintense laser fields; (ii) laser-induced molecular stabilization and chemical bond hardening in strong laser fields.     

Time‐dependent wave packet approach to Rabi oscillation in strong laser field

The phenomenon of Rabi oscillation is obtained in the investigation of the NO multiphoton ionization (MPI) in femtosecond laser fields. The “split operator‐Fourier transform” method of wave packet propagation is used in the representation of Rabi oscillation of population in each electronic state of NO molecule. The origin of Rabi oscillation and the effect on multiphoton ionization is analyzed. The high‐frequency oscillation riding on the top of Rabi oscillation is attributed to the nonrotating wave component in strong laser fields. Also illustrated is that through adjusting the pump‐probe delay time and the laser intensity appropriately the control of the ionization yield can be realized. This idea may be important for the laser control of chemical reaction. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 95: 30–36, 2003     

Multiphoton excitation of an ammonia molecule in laser fields

The multiphoton excitation of NH3 in laser fields is discussed using the second quantization and unitary transformations.The stretch-vibration energy spectrum obtained from an optimized Hamiltonian is in good agreement with that of experiments.The changes in transition probabilities with the frequencies of laser fields and the lime-dependent transition probabilities at a field intensity of 1.1×10-8 W/cm2 are presented.Finally,the energy absorption is calculated.     

C_(∞v)对称分子在激光场中多光子激发的同位素效应

用二次量子化方法讨论了ＸＹ 分子在激光场中的多光子激发,包括对分子伸缩振动能级的计算,讨论了跃迁概率的长时间平均值和同位素效应     

Multiphoton dissociation of C3F6O

Major characteristics of multiphoton absorption and multiphoton dissociation of hexafluoropropene oxide (HFPO) were studied. Spectral relationships of the average number of IR photons absorbed per molecule and the yield of multiphoton dissociation were determined in the range of 1040-985 cm^–1 at different laser fluences. At the laser line 1025.3 cm^–1, the effect of collisions with buffer gases on the HFPO multiphoton absorption and multiphoton dissociation was studied and theq-factor was determined (q = O.6 at= 0.55J cm^–2). Characteristic features of HFPO decomposition under collisional conditions (p _HFPO> 0.1 Torr) were discussed. An anomalous difference in the values for quantum efficiency of multiphoton dissociation for long-wave and short-wave wings of HFPO absorption band was revealed. A procedure for correlating the experimental and theoretical data on the yield of multiphoton dissociation (when theq-factor is unknown) was suggested, and corresponding calculations were performed for the frequency 989.6 cm^–1.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1927–1932, November, 1994.     

Neutral Dissociation of Superexcited Nitric Oxide Induced by Intense Laser Fields

Superexcited states of NO molecule and their neutral dissociation processes have been stud-ied both experimentally and theoretically. Neutral excited N^? and O^? atoms are detected by fluorescence spectroscopy for the NO molecule upon interaction with 800 nm intense laser radiation of duration 60 fs and intensity 0.2 PW/cm². Intense laser pulse causes neu-tral dissociation of superexcited NO molecule by way of multiphoton excitation, which is equivalent to single photon excitation in the extreme-ultraviolet region by synchrotron ra-diation. Potential energy curves (PECs) are also built using the calculated superexcited state of NO⁺. In light of the PECs, direct dissociation and pre-dissociation mechanisms are proposed respectively for the neutral dissociation leading to excited fragments N^? and O^?.     

Infrared multiphoton decomposition and the possibilities of laser-based heavy water processes

The selective multiphoton decomposition (MPD) process has the potential to provide a stand-alone heavy water process which is competitive with conventional processes. Twelve criteria are discussed for selecting a working molecule to give a process economically competitive with the Girdler-Sulphide process. The dependence of the MPD process on interacting parameters such as laser fluence, intensity and bandwidth as well as collisional effects are discussed. Finally, several potential working molecules are reviewed.     

Time-Dependent quantum theory. IV. Effect of lattice relaxation on the optical spectra

The absorption and emission spectra of a diatomic “molecule” connected to an unstrained linear crystal are calculated for the circumstance where the diatomic undergoes a change of equilibrium internuclear separation in the electronic transition. The expansion (or contraction) of the diatomic results in a frequency dependent line-width in the customary Lorentzian expression, and is manifested in the absorption spectrum as an asymmetric tailing to the blue, and in the emission spectrum as an asymmetric tailing to the red. The interaction of the diatomic with the lattice also produces a blue-shift of the absorption spectrum and a red-shift of the emission spectrum. An important consequence of the asymmetry is the apparent loss of integrated intensity of the line. The striking similarity, both in the width and the over-all shape, of the emission line calculated here with those observed in the Vegard–Kaplan band of N₂ dissolved in rare gas crystals is discussed.     

CO2 laser excitation of triethylsilane: Time resolved luminescence of diethylsilyl radical

The infrared multiphoton excitation of triethylsilane in the gas phase, with a pulsed CO₂ laser at high intensities (I > 700 MW/cm²), produced an intense luminescence. The spectrum and time profile of this luminescence was studied as a function of pressure, and laser frequency. The radiative lifetime of this emission was 357 ± 10 ns, and the quenching rates by Cl₂ and NO were determined from lifetime measurements. A reasonable mechanism for the interpretation of this luminescence involves the initial infrared multiphoton decomposition of triethylsilane, followed by the secondary infrared multiphoton excitation of the primary photofragment diethylsilyl radical, which subsequently undergoes relaxation to an excited electronic state. The addition of O₂ resulted in a new chemiluminescence at shorter wavelengths, which corresponds to the SiO* chromophore group. © 1994 John Wiley & Sons, Inc.     

Spatial Taming and Trapping of Molecules

Molecular beam techniques for study of collisional and spectroscopic processes have recently been enhanced by use of static electric or magnetic fields to orient or align molecules with permanent dipole moments. A more general method is now in prospect, applicable both to alignment and to spatial trapping of molecules. This exploits the anisotropic interaction of the electric field vector of intense laser radiation with the dipole moment induced in a polarizable molecule by the laser field. The interaction creates directional superpositions of field-free states that correspond to oblate spheroidal wavefunctions, with eigenenergies that decrease with increasing field strength. We suggest that this polarizability interaction produces the marked alignment found in laser-induced dissociative ionization of CO by the Saclay group. We also present calculations illustrating the feasibility of spattal trapping. In combination with supermirror focussing and buffer-gas cooling, an intense infrared laser can typically confine molecules for long-times (-hours) within a small (-picoliter) and cold (?1°K) “pocket of light.”     

Numerical coupled Liouville approach: Application to second hyperpolarizability of molecular aggregate

In our previous study [Int. J. Quant. Chem., to appear], we have developed a novel numerical calculation scheme for a dynamics of quantum network for linear molecular aggregates under intense time‐dependent electric fields. In this approach, each molecule is assumed to be an electric dipole arranged linearly with an angle from the longitudinal axis, and the molecular interactions are taken into account by adding the radiations from these dipoles to the external electric fields. The effects of the radiations from all the dipoles involve the intermolecular distance, the speed of light, retarded polarization, and its first‐ and second‐order time derivatives at the position of each dipole. The quantum dynamics is performed by solving coupled Liouville equations composed of the Liouville equation for each dipole. In the present study, we develop a calculation approach of nonperturbative second hyperpolarizability γ in our novel approach and examine the γ of dimer models composed of two‐state molecules under the one‐photon near resonant intense laser fields. Similar phase transition‐like behavior in the field‐intensity dependence of the γ is observed. We also investigate the second hyperpolarizability spectra in the three‐photon resonant region for dimers composed of three‐state molecules, which mimic the electronic states of allyl cation. Contrary to the one‐photon resonant case, phase transition‐like behavior is not observed in the intensity dependence of γ in the three‐photon resonant region. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 71: 295–306, 1999