Initial Vibrational State Research Articles

Non-Born–Oppenheimer stereodynamics study for the D+ + H2 (v, j = 0) reaction using coherent switching with decay of mixing method

A non-Born–Oppenheimer (BO) investigation using coherent switching with decay of mixing method is carried out for both reactive non-charge transfer and charge transfer channels of reaction D+ + H2 (v, j = 0). For the non-charge transfer channel, it is found that the non-BO effect has a small influence on the differential cross section, but it has a large impact on the rotational polarization of the HD product, which is reflected by the joint distribution P(θr, ϕr). And it is also found that the polarization of the charge transfer products shows a quite different form. The rotational polarizations are also investigated at various collision energies and initial vibrational states for both reactive channels.

Controlled Teleportation of the Two-Ion Entangled State

A simple scheme for controlled teleportation of an arbitrary two-ion entangled state using a bell and GHZ entangled state as quantum channel is proposed in trapped ion systems. An arbitrary two-ion entangled state can be teleported perfectly with the help of the cooperation. In our scheme the ions are simultaneously excited by a laser. Our scheme is insensitive to both the initial vibrational state and heating. The probability of the success in our scheme is 1.0.

Quasiclassical trajectory study of the rotational mode specificity in the O((3)P) + CHD3(v1 = 0, 1, JK) → OH + CD3 reactions.

Quasiclassical trajectory computations on an ab initio potential energy surface reveal that rotational excitation can significantly enhance the reactivity of the ground-state and CH stretching-excited O((3)P) + CHD3(v1 = 0,1, JK) → OH + CD3 reactions. The state-specific rotational effects investigated up to J = 8 show that the K = 0 (tumbling rotation) enhancement factors can be as large as 1.5-3.5 depending on J and the collision energy, whereas the K = J (spinning rotation about the CH axis) excitations do not have any significant effect on the reactivity. The shapes of the opacity functions and scattering angle distributions depend on the initial vibrational state, but show virtually no JK dependence. The origin of the K = 0 rotational enhancements is that the tumbling rotation enlarges the range of the reactive initial attack angles, thereby increasing the reactivity.

Quantum Teleportation of an Arbitrary Two-Ion State by Using a Genuine Four-Ion Entangled State in Ion-Trap Systems

We propose a scheme to realize the deterministic quantum teleportation of an arbitrary two-ion state by using a genuine four-ion entangled state in ion-trap systems. The scheme does not involve Bell-state measurements and only needs to make the single-ion measurements. Our scheme is insensitive to both the initial vibrational state and heating, which is of importance in view of experiment.

Validity of the site-averaging approximation for modeling the dissociative chemisorption of H2 on Cu(111) surface: a quantum dynamics study on two potential energy surfaces.

A new finding of the site-averaging approximation was recently reported on the dissociative chemisorption of the HCl/DCl+Au(111) surface reaction [T. Liu, B. Fu, and D. H. Zhang, J. Chem. Phys. 139, 184705 (2013); T. Liu, B. Fu, and D. H. Zhang, J. Chem. Phys. 140, 144701 (2014)]. Here, in order to investigate the dependence of new site-averaging approximation on the initial vibrational state of H2 as well as the PES for the dissociative chemisorption of H2 on Cu(111) surface at normal incidence, we carried out six-dimensional quantum dynamics calculations using the initial state-selected time-dependent wave packet approach, with H2 initially in its ground vibrational state and the first vibrational excited state. The corresponding four-dimensional site-specific dissociation probabilities are also calculated with H2 fixed at bridge, center, and top sites. These calculations are all performed based on two different potential energy surfaces (PESs). It is found that the site-averaging dissociation probability over 15 fixed sites obtained from four-dimensional quantum dynamics calculations can accurately reproduce the six-dimensional dissociation probability for H2 (v = 0) and (v = 1) on the two PESs.

Wave packet and statistical quantum calculations for the He + NeH+ → HeH+ + Ne reaction on the ground electronic state

A real wave packet based time-dependent method and a statistical quantum method have been used to study the He + NeH(+) (v, j) reaction with the reactant in various ro-vibrational states, on a recently calculated ab initio ground state potential energy surface. Both the wave packet and statistical quantum calculations were carried out within the centrifugal sudden approximation as well as using the exact Hamiltonian. Quantum reaction probabilities exhibit dense oscillatory pattern for smaller total angular momentum values, which is a signature of resonances in a complex forming mechanism for the title reaction. Significant differences, found between exact and approximate quantum reaction cross sections, highlight the importance of inclusion of Coriolis coupling in the calculations. Statistical results are in fairly good agreement with the exact quantum results, for ground ro-vibrational states of the reactant. Vibrational excitation greatly enhances the reaction cross sections, whereas rotational excitation has relatively small effect on the reaction. The nature of the reaction cross section curves is dependent on the initial vibrational state of the reactant and is typical of a late barrier type potential energy profile.

Electron scattering from the molecular hydrogen ion and its isotopologues

We have extended the $ab$ $initio$ convergent close-coupling method to electron scattering from the vibrationally excited molecular hydrogen ion and its isotopologues. Calculations have been performed within the adiabatic-nuclei approximation. Results are presented for dissociative excitation and ionization as a function of the initial vibrational state of the molecules. Comparison with experiment is excellent across the energy range from near threshold to 1 keV.

Dissociative chemisorption of methane on metal surfaces: tests of dynamical assumptions using quantum models and ab initio molecular dynamics.

The dissociative chemisorption of methane on metal surfaces is of great practical and fundamental importance. Not only is it the rate-limiting step in the steam reforming of natural gas, the reaction exhibits interesting mode-selective behavior and a strong dependence on the temperature of the metal. We present a quantum model for this reaction on Ni(100) and Ni(111) surfaces based on the reaction path Hamiltonian. The dissociative sticking probabilities computed using this model agree well with available experimental data with regard to variation with incident energy, substrate temperature, and the vibrational state of the incident molecule. We significantly expand the vibrational basis set relative to earlier studies, which allows reaction probabilities to be calculated for doubly excited initial vibrational states, though it does not lead to appreciable changes in the reaction probabilities for singly excited initial states. Sudden models used to treat the center of mass motion parallel to the surface are compared with results from ab initio molecular dynamics and found to be reasonable. Similar comparisons for molecular rotation suggest that our rotationally adiabatic model is incorrect, and that sudden behavior is closer to reality. Such a model is proposed and tested. A model for predicting mode-selective behavior is tested, with mixed results, though we find it is consistent with experimental studies of normal vs. total (kinetic) energy scaling. Models for energy transfer into lattice vibrations are also examined.

Generation of a Three-Ion GHZ-Like State in Ion-Trap Systems

We propose a scheme for the generation of a three-ion GHZ-like state in ion-trap systems. In our scheme the ions are simultaneously excited by a laser. Our scheme is insensitive to both the initial vibrational state and heating if the system remains in the Lamb-Dicke regime.

Theoretical investigation of the competitive mechanism between dissociation and ionization of H₂⁺ in intense field.

The competitive mechanism between dissociation and ionization of hydrogen molecular ion in intense field has been theoretically investigated by using an accurate non-Born-Oppenheimer method. The relative yield of fragments indicates that the dissociation and ionization channels are competitive with the increasing laser intensity from 5.0 × 10(13) to 2.0 × 10(14) W/cm(2). In the case of intensity lower than 1.0 × 10(14) W/cm(2), the dissociation channel is dominant, with a minor contribution from ionization. The mechanism of dissociation includes the contributions from the bond softening, bond hardening, below-threshold dissociation, and above-threshold dissociation, which are strongly dependent on the laser intensity and initial vibrational state. Furthermore, the ionization dominates over the dissociation channel at the highest intensity of 2.0 × 10(14) W/cm(2). The reasonable origin of ionization is ascribed as the above-threshold Coulomb explosion, which has been demonstrated by the space-time dependent ionization rate. Moreover, the competition mechanism between dissociation and ionization channels are displayed on the total kinetic energy resolved (KER) spectra, which could be tested at current experimental conditions.

X-ray lasing in diatomic molecules

We predict high-gain x-ray lasing in diatomic molecules by ultrafast core ionization of the C K- and O K-edges in CO and the N K-edge in N2 with an x-ray free-electron laser source. We solve generalized Maxwell-Bloch equations, keeping track of the electronic and nuclear degrees of freedom. By controlling the molecular alignment and thereby the alignment of the transition dipole moment polarization control of the emitted x-ray radiation is achievable. Despite the broad fluorescence bandwidth, the amplified x-ray emission shows a narrow spectrum. Preparing the initial vibrational quantum state, the x-ray emission frequency can be tuned within the fluorescence band.

Quasi-Classical Trajectory Study of the Scalar Properties of the Reaction N(<sup>4</sup>S)+H<sub>2</sub>(<i>v</i>=0,1,2,3;<i> j</i>=0)→NH+H

Quasi-classical trajectory dynamical calculations of the title reactions have been performed on an accurate NH2 potential energy surface [Poveda LA, Varandas AJC, Phys Chem Chem Phys 7:2867,2005] over the collision energy range of 25-80 kcal mol-1. The reaction cross sections, variation of internuclear distances of N-Ha, N-Hb and Ha-Hb, and the reaction rate constants are reported for various initial vibrational and rotational states of H2 (v=0-3; j=0) molecules. The reaction cross section in the ground vibrational state of H2 and the rate constant over the thermal distribution of initial vibrational states of H2 are compared with other theoretical results and existing experimental results in the literature, showing good agreement.

Theoretical Exploration of the Isotopic Effect on Molecular High-Order Harmonic Generation

ABSTRACT The isotopic effect on the generation of the molecular high-order harmonics is studied by numerically solving the one-dimensional time-dependent Schrödinger equation when the model hydrogen molecule ions/hydrogen deuterium molecule ions are exposed to an intense laser pulse. To explain the effect more clearly, not only the ionization probabilities but also the electron–nuclear probability density distributions and time-frequency profiles are calculated. The results show that more intense harmonics are generated in the asymmetric diatomic molecule ions/hydrogen deuterium molecule ions than those of hydrogen molecule ions. Moreover, the interference minimum in the harmonic spectra is investigated by adjusting the laser intensity and the initial vibrational state. It is shown that the interference minimum is sensitive to the laser intensity and the initial vibrational level for hydrogen molecule ions; in contrast, it is only dependent on the initial vibrational level for hydrogen deuterium molecule ions.

Stereodynamics investigation of F + HO → HF + O(1D) on the ground singlet potential energy surface by means of the quasi-classical trajectory method

The stereodynamics calculation of F + HO → HF + O(1D) was carried out using the quasi-classical trajectory method on the 11A′ potential energy surface provided by Gomez-Carrasco et al. (Chem. Phys. Lett. 2007, 435, 188). The effect of the collision energy, isotopic substitution, and different initial ro-vibrational states on the reaction is discussed. It is found that for the initial ground state of HO (v = 0, j = 0), the degree of the forward scattering and the product polarizations remarkably change as the collision energy varies. Isotopic effect leads to the increase of alignment and decrease of orientation of product rotational angular momentum. Moreover, the P(θr) distribution and P(φr) distribution change noticeably by varying the initial vibrational number. The initial vibrational excitation plays a more important role in the enhancement of alignment and orientation distribution of j′ for the title reaction. Although the influence of the initial rotational excitation effect on the aligned and oriented distribution of product is not stronger than that of the initial vibrational excitation effect, the initial rotational excitation makes the alignment of the product rotational angular momentum decrease to some extent. The probabilities show that the reactivity of the title reaction strongly depends on the initial vibrational state.

Time-resolved laser Coulomb explosion imaging using few-cycle intense laser pulses: Application to exploding CS2 in highly charged states

Ion-coincidence momentum imaging of three-body Coulomb explosion of CS2, CS2z+→Sp++Cq++Sr+ (z=p+q+r), in few-cycle intense laser fields (9fs, ∼1015W/cm2) is presented. It is shown that the momentum distributions of fragment ions produced from CS210+ are well reproduced by a classical explosion model incorporating the coordinate and momentum distributions of the initial ground vibrational state of CS2. On the other hand, a significant deviation is observed for CS23+ due to the non-Coulombic character of the potential energy surfaces. Coulomb explosion imaging is applied to real-time probing of Coulomb exploding CS2 in highly charged states, using a pair of intense few-cycle laser pulses. It is shown that the explosion proceeds in a different time scale depending on the charge state, mostly along the linear geometry during the bond-breaking of the two CS bonds.

Vibrational Mode Multiplexing of Ultracold Atoms

Sending multiple messages on qubits encoded in different vibrational modes of cold atoms or ions along a transmission waveguide requires us to merge first and then separate the modes at input and output ends. Similarly, different qubits can be stored in the modes of a trap and be separated later. We design the fast splitting of a harmonic trap into an asymmetric double well so that the initial ground vibrational state becomes the ground state of one of two final wells, and the initial first excited state becomes the ground state of the other well. This might be done adiabatically by slowly deforming the trap. We speed up the process by inverse engineering a double-function trap using dynamical invariants. The separation (demultiplexing) followed by an inversion of the asymmetric bias and then by the reverse process (multiplexing) provides a population inversion protocol based solely on trap reshaping.

Ionization Channels of the Molecular Ion H+2 in Intense Laser Field

Ionization channels of the molecular ion H+2 for various initial vibrational states in intense laser field (80 fs, 800 nm, I = 6.8 × 1013 W/cm2) are theoretically investigated by numerically solving the time-dependent Schrödinger equation. The results confirm that the channels largely depend on the selection of initial vibrational states by analyzing the variations of peak locations in the nuclear initial kinetic-energy-release spectra. Furthermore, the selection of the ionization channels is sensitive to the wavelength of the laser pulse. In addition, time-dependent competition between direct multi-photon ionization and charge-resonance-enhanced ionization are is discussed.

X-ray lasing in the CO molecule

We theoretically demonstrate the feasibility of x-ray lasing in the CO molecule by the core ionization of the C K- and O K-shell by x-ray free-electron laser sources. Our numerical simulations are based on the solution of generalized Maxwell–Bloch equations, accounting for the electronic and nuclear degrees of freedom. The amplified x-ray emission pulses have an extremely narrow linewidth of about 0.1 eV and a pulse duration shorter than 30 fs. We compare x-ray lasing transitions to the three lowest electronic states of singly ionized CO. The dependence of the lasing efficiency on the spectral width of the x-ray fluorescence band, value and orientation of the electronic transition dipole moment, lifetime of the core-excited state and the duration of the pump pulse is analysed. Using a pre-aligned molecular ensemble substantially increases the amplified emission. Moreover, by controlling the molecular alignment and thereby the alignment of the transition dipole moment polarization, the control of the emitted x-ray radiation is achievable. Preparing the initial vibrational quantum state, the x-ray emission frequency can be tuned within the fluorescence band. The present scheme is applicable to other diatomic systems, thereby extending the spectral range of coherent x-ray radiation sources based on stimulated x-ray emission on bound transitions.

A theoretical study of the stereodynamics on the abstraction reactions H/D + HS/DS

The quasi-classical trajectory (QCT) method is employed to calculate the stereodynamics of the abstraction reactions H/D + HS/DS based on an accurate potential energy surface [Lü S J, Zhang P Y, Han K L and He G Z 2012 J. Chem. Phys. 136 094308]. The reaction cross sections of the title reaction are computed, and the vector correlations for different collision energies and different initial vibrational states are presented. The influences of the collision energy and reagent vibration on the product polarization are studied, and the product polarizations of the title reactions are found to be distinctly different, which arises from the different mass factors, collision energies, and reagent vibrational states.

Theoretical Exploration of the Isotopic Effect on Nuclear Dynamics in Coulomb Explosion

The isotopic effect on nuclear dynamics in Coulomb explosion for various initial vibrational states of H2+ and HD+ in intense laser (80 fs, 800 nm, I = 6.8 × 1013 W/cm2) is theoretically investigated by numerically solving the time-dependent Schrödinger equation. The calculated results confirm that the effect we discussed by paying close attention to the comparative analysis of peak locations in the nuclear kinetic-energy-release spectra largely depends on the selection of the initial vibrational states. Furthermore, it is the special isotope effect case about the vibrational state υ = 5 that has been studied in depth. We also discuss the time-dependent spectrum at υ = 7, which can reveal the difference in nuclear wavepacket motion between H2+ and HD+ in the time region in which charge-resonance enhanced ionization takes place.