Time-dependent Quantum Wave Packet Method Research Articles

Theoretical studies of femtosecond photoionization for the Na<sub>2</sub> molecule

Multiphoton ionization of the Na2 molecule by a single phase shaped fem- tosecond laser pulse has been theoretically studied using time-dependent quantum wave packet method including the effect of molecular rotation. We analyze the tempo- ral development of the population and further discuss the molecular motion by map- ping the rovibrational wave packet propagation in the excited state. The calculated results show a strong dependence of the kinetic energy-resolved photoelectron spectra on the laser chirp directions and the pulse duration. PACS: 33.80.Rv

Stimulated Raman adiabatic passage through permanent dipole moment transitions

The rovibrational dynamics of stimulated Raman adiabatic passage (STIRAP) through permanent dipole moment transitions are investigated theoretically using a time-dependent quantum wave packet method for the ground electronic state of an HF molecule. The two basic STIRAP processes, {Lambda} and ladder systems, are simulated. The calculated results show that nearly 100% of the population can be transferred to the target state. Besides the interested transitions, the pulses can induce other transitions which affect the dynamics of STIRAP. The final populations of the initial and target states depend on delay time.

Study on wave packet dynamics of E1 σg+ state of Li2 with femtosecond-resolved photoelectron spectra

Wave packet dynamics of the Li2 molecule are investigated by using the time-dependent quantum wave packet method, and the time-resolved photoelectron spectra of the Li2 molecule are calculated. The time-resolved wave packet theory is used to reasonably interpret the phenomena of the photoelectron spectra for different parameters. Our calculation shows that the loss of the wave packets in the shelf state area of E1 σ+g plays a prominent role in the process of photoionization with the increase of the delay time. Moreover, the oscillation of the wave packet on the E1 σ+g curve symbolizes a decreasing process of energy.

Quantum wave packet study of the He + CaH reaction

The He + CaH inelastic reaction is studied by a time-dependent quantum wave packet method, using the most recent potential energy surface reported by Groenenboom and Balakrishnan [1]. The state-to-state and state-to-all transition probabilities for total angular momentum J = 0 have been calculated in a broad range of collision energies. Integral cross sections and rate constants have been calculated from the wave packet transition probabilities by means of J-shifting approximation based on a capture model and a uniform J-shifting method for J > 0.

THEORETICAL STUDY OF ABOVE THRESHOLD DISSOCIATION OF HD+ IN FEMTOSECOND LASER FIELDS

The above threshold dissociation (ATD) of the HD+ molecular ion in a linearly polarized femtosecond laser field is theoretically studied using three-dimensional time-dependent quantum wave packet method. Based on the Born–Oppenheimer approximation (BOA), calculations are performed on two electronic states, the ground state 1sσ and the excited state 2pσ. The energy-dependent distributions of the dissociated fragments, resulting from the ATD, are calculated by using an asymptotic-flow expression in the momentum space. The numerical results demonstrate that, in the laser field of wavelength λ = 800 nm and full-width at half-maximum (FWHM) τ = 30 fs , only two-photon dissociation is observable at a weaker pulse peak intensity, 5.0 × 1012 W cm -2, while at an intense intensity, 1.5 × 1015 W cm -2, the dissociated fragments resulting from four-photon absorption dominates over the photodissociation process. These results are consistent with the experimental observation of Orr et al. [Orr PA et al., Phys Rev Lett98:163001, 2007]. The ac Stark-shift caused by intense laser field will change the kinetic energies of the fragments. The ATD phenomena are quantitatively interpreted in terms of the concept of light-induced potential. The molecular rotation and alignment have some effects on the kinetic energy spectrum of the dissociated fragments. The molecular rotation reduces the ac Stark-shift and broadens the peaks of kinetic energy spectra of the dissociated fragments. However, the intense laser field can effectively align the molecule and is helpful to increase the ATD probability. The ATD spectrum is related to the initial quantum numbers J0 and M0 of the molecule. The ATD spectrum of HD+ is calculated at a limited thermal temperature.

Interference of dissociating wave packets in the I2 molecule driven by femtosecond laser pulses

The interference between two dissociating wave packets of the I2 molecule driven by femtosecond laser pulses is theoretically studied by using the time-dependent quantum wave packet method. Both the internuclear distance- and velocity-dependent density functions are calculated and discussed. It is demonstrated that the interference pattern is determined by the phase difference and the delay time between two pump pulses. With two identical pulses with a delay time of 305 fs and a FWHM of 20 fs, more interference fringes can be observed, while with two pump pulses with a delay time of 80 fs and a FWHM of 20 fs, only a few interference fringes can be observed.

Quantum wave packet study of the [formula omitted] reaction

The C ( 1 D ) + H 2 reaction was studied by the time-dependent quantum wave packet method. Coupled channel calculations have been carried out to get initial state-specified ( ν 0 = 0 , j 0 = 0 ) integral cross section and rate constant. All projection quantum numbers K were considered for each total angular momentum J value. At room temperature, the rate constant is reasonably in good agreement with the experimental value. Comparisons between the integral cross section and other theoretical results were also made. Initial state-specified ( ν 0 = 0 , j 0 = 1 , 2 ) rate constants were calculated by using the uniform J-shifting approximation. Only a slight increase for initial rotational excitations of H 2 was found.

Theoretical Investigation of Femtosecond-Resolved Photoelectron Spectra of the Li2 Molecule

The time-dependent quantum wave packet method is used to investigate the dynamics for the Li2 molecule, and the time-resolved photoelectron spectra (TRPES) of the Li2 molecule are calculated. At the short delay time, the particular phenomenon of TRPES with four peaks is qualitatively interpreted in a dressed state picture by analyzing wave packet motion on light-induced potential (LIP). The significant difference in the electronic structure of between the inner and outer turning points has an impact on the TRPES. The control for the first excited state of the initial wave packet is discussed.

CONTROLLING WAVE PACKET INTERFERENCE OF DISSOCIATING MOLECULES BY SHAPING LASER PULSES IN FREQUENCY DOMAIN

The interference of dissociating wave packets for the Br 2 molecule in femtosecond laser field is studied theoretically using time-dependent quantum wave packet method. The interference of dissociating wave packets can be determined by the spectrum of laser field. By shaping laser pulses in frequency domain, the corresponding R- and v-dependent density functions can be effectively controlled. Compared with the 2-pulse excitation scheme, the resolution of the interference patterns can be improved by using 3- and 4-pulse excitation schemes. The dissociating velocity can be steered by varying laser parameters.

AN ACCURATE QUANTUM DYNAMICS STUDY OF THE N+OH REACTION

Using time-dependent quantum wave packet method, the total reaction probabilities and thermal rate constants (TRC) are calculated for the exoergic reaction N+OH on the 3A″ potential energy surface (Guadagnini R, Schatz GC, Walch SP, J Chem Phys102:774, 1995) under both coupled-state or centrifugal sudden (CS) approximation and Coriolis-coupled or close-coupling (CC) approach. As a result, the difference between CS and CC total reaction probabilities gets more prominent when the value of total angular momentum J increases. As for TRC, the calculated results are in excellent agreement with earlier experimental measurements.

Full six-dimensional nonadiabatic quantum dynamics calculation for the energy pooling reaction O2(aΔ1)+O2(aΔ1)→O2(bΣ1)+O2(XΣ3)

Six new potential energy surfaces of four singlet states and two triplet states for the title oxygen molecule reaction along with the spin-orbit coupling among them have been constructed from the complete active space second-order perturbation theory with a 6-311+G(d) basis. Accurate integral cross sections are calculated with a full six-dimensional nonadiabatic time-dependent quantum wave packet method. The thermal rate constant based on the integral cross sections agrees well with the result of the experimental measurements, and the intersystem crossing effects are also discussed in this electronic energy-transfer process.

Steering population transfer via continuum structure of the Li 2 molecule with ultrashort laser pulses

The population transfer via continuum for the Li 2 molecule is theoretically investigated using time-dependent quantum wave packet method. With proper laser pulses, a high efficient population transfer can be achieved, and the selective ro-vibrational population transfer via continuum can be realized. The population transfer process is qualitatively interpreted employing the concept of light-induced potential. The effect of molecular rotation on the population transfer and the angular distribution of population is described in detail.

Control of photoassociation reaction F+H→HF with ultrashort laser pulse

The laser-induced vibrational state-selectivity of product HF in photoassociation reaction H+F→HF is theoretically investigated by using the time-dependent quantum wave packet method. The population transfer process from the continuum state down to the bound vibrational states can be controlled by the driving laser. The effects of laser pulse parameters and the initial momentum of the two collision atoms on the vibrational population of the product HF are discussed in detail. Photodissociation accompanied with the photoassociation process is also described.

Time-dependent Quantum Wave Packet Study of F+HCl and F+DCl Reactions

The F+HCl and F+DCl reactions are studied by the time-dependent quantum wave packet method, using the most recent potential energy surface reported by Deskevich et al.. Total reaction probabilities for a number of initial ro-vibrational states of HCl and DCl diatomic moiety are presented in the case of total angular momentum J=0. It is found that for both reactions the initial rotational excitation of the diatomic moiety enhances greatly the reaction probabilities but this effect is more significant for F+HCl system. This is mainly due to larger rotational constant of the HCl reagent. The initial vibrational excitation of the diatomic moiety has little effect on the reactivity for both systems except shifting down the collision energy threshold. The results indicate that the reaction coordinates for these two systems are effectively along rotational freedom degree. More quantum phenomena, such as tunneling and resonance, are observed in F+HCl reaction than F+DCl reaction, and for the initial states studied, the reactivity of the later is lower. Different skewing angles of these two systems account for these isotopic differences.

A Quantum Wave Packet Dynamics Study of the N(2D) + H2 Reaction

We report a dynamics study of the reaction N((2)D) + H(2) (v=0, j=0-5) --> NH + H using the time-dependent quantum wave packet method and a recently reported single-sheeted double many-body expansion potential energy surface for NH(2)(1(2)A' ') which has been modeled from accurate ab initio multireference configuration-interaction calculations. The calculated probabilities for (v=0, j=0-5) are shown to display resonance structures, a feature also visible to some extent in the calculated total cross sections for (v=0, j=0). A comparison between the calculated centrifugal-sudden and coupled-channel reaction probabilities validate the former approximation for the title system. Rate constants calculated using a uniform J-shifting scheme and averaged over a Boltzmann distribution of rotational states are shown to be in good agreement with the available experimental values. Comparisons with other theoretical results are also made.

The nonadiabatic quantum dynamics of the F( 2P 1/2, 2P 3/2) + HD reaction on modified Alexander, Stark, and Werner potential energy surfaces

In this Letter, the barrier height of the Alexander, Stark and Werner (ASW) potential energy surfaces is adjusted using the scale external correlation technique, which lowers by 0.016 eV the lowest barrier for the bent configuration and lowers by 0.015 eV the collinear barrier of the ASW diagonal diabatic potentials. The calculated integral cross sections for the reaction of F( 2P 3/2) with HD, using the time-dependent quantum wave packet method, show that the position of the resonance is about 0.026 eV, which is in the good agreement with experimental data.

TIME-DEPENDENT QUANTUM MECHANICAL TREATMENT OF He–CO INELASTIC SCATTERING

The state-to-state and state-to-all reaction probabilities for He + CO (v,j)→ He + CO (v',j') reaction at zero total angular momentum have been calculated by using a time-dependent quantum wave packet method. The time-dependent method used is based on Fourier Grid and Discrete Variable Representation (DVR) techniques. The time-dependent propagation of the wave packet is accomplished by an expansion in terms of modified complex chebyshev polynomials. The results show that the He + CO reaction is not reactive in the studied energy range.

Reactive and inelastic scattering probabilities for the Cl+H 2 scattering: time-dependent calculations

In this paper, three-dimensional Cl+H 2( ν, j)→ClH( ν′, j′)+H and Cl+H 2( ν, j)→Cl+H 2( ν′, j′) reactions at zero total angular momentum have been studied by using a time-dependent quantum wave packet method. Reactive and inelastic scattering probabilities for a broad range of energy are calculated.

The investigation of spin-orbit effect for the F((2)P)+HD reaction.

In this paper, we employ the time-dependent quantum wave packet method to study the reaction of F((2)P(3/2), (2)P(1/2)) with HD on the Alexander-Stark-Werner potential energy surface. The reaction probabilities and total integral cross sections of the spin-orbit ground and excited states for the two possible products of the system are calculated. Because the reaction channel of the excited spin-orbit state is closed at the resonance energy, the resonance feature does not appear in the reaction probabilities and cross section for the F((2)P(1/2))+HD(v=j=0)-->HF+D reaction, in contrast with that found for the ground spin--orbit state. We also compare the average cross sections of the two possible products with the experimental measurement. The resonance peak in the present average cross section for the HF+D product is slightly larger than the experimental result, but much smaller than that of the single-state calculations on the potential energy surface of Stark and Werner. It seems that the spin--orbit coupling would play a relatively important role in this reaction. Moreover, the isotope effects of the ground and excited spin--orbit states and the reactivity of the two product channels from the excited spin--orbit state are presented.

Nonadiabatic photodissociation dynamics

The photodissociation dynamics of the triatomic (or pseudo-triatomic) system in the nonadiabatic multiple electronic states is investigated by employing a time-dependent quantum wave packet method, while the time propagation of the wave packet is carried out using the split-operator scheme. As a numerical example, the photodissociation dynamics of CH3I in three electronic states 1Q1(A′), 1Q1(A″), and 3Q0+ is studied and CH3I is treated as a pseudotriatomic model. The absorption spectra and product vibrational state distributions are calculated and compared with previous theoretical work. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005