Quantum Wave Packet Calculations Research Articles

Construction of diabatic potential energy surfaces for the SiH2+ system and dynamics studies of the Si+(2P1/2, 3/2) + H2 reaction.

The construction of diabatic potential energy surfaces (PESs) for the SiH2+ system, related to the ground (12A') and excited states (22A'), has been successfully achieved. This was accomplished by utilizing high-level abinitio energy points, employing a neural network fitting method in conjunction with a specifically designed function. The newly constructed diabatic PESs are carefully examined for dynamics calculations of the Si+(2P1/2, 3/2) + H2 reaction. Through time-dependent quantum wave packet calculations, the reaction probabilities, integral cross sections (ICSs), and differential cross sections (DCSs) of the Si+(2P1/2, 3/2) + H2 reaction were reported. The dynamics results indicate that the total ICS is in excellent agreement with experimental data within the collision energy range studied. The results also indicate that the SiH+ ion is hardly formed via the Si+(2P3/2) + H2 reaction. The results from the DCSs suggest that the "complex-forming" reaction mechanism predominates in the low collision energy region. Conversely, the forward abstraction reaction mechanism is dominant in the high collision energy region.

Revealing the vibronic coupling effects in the size-dependent optical properties of cycloparaphenylene dications

We explain the visible and near-infrared optical properties of low-lying singlet excited states (S and S) of [5]-, [7]- and [9]cycloparaphenylene dications (CPPs). A narrow energy gap (<150 cm) separates these states at the Franck–Condon point of the individual molecule. The energy gap increases upon increasing the molecular size. Consequently, [5]CPP possesses highly overlapping S and S absorption bands. The overlap between these bands decreases and the resulting composite spectrum appears broader, particularly for [9]CPP. Theoretical spectra generated using quantum wavepacket calculations within the linear vibronic coupling approach match well with the experiment. Our findings reveal near-degenerate S and S minima, highlighting the relevance of both these states while assigning experimental fluorescence emission properties of CPPs.

Possible Formation and Destruction of the OD+ Ions in the Interstellar Medium.

The OH+ ion is an important constituent of the interstellar medium (ISM). It can be used as a probe of cosmic ray and X-ray ionization rates in molecular clouds as well as a tracer of oxygen chemistry. The deuterated variant of OH+, the OD+ ion, may also be present in the ISM despite the fact that it has not been detected yet. In this paper, we aim at providing quantitative insight into the OD+ chemistry and at accurately studying the possible formation and destruction processes of OD+ in the ISM. We study the formation and destruction of OD+ through the O+ + HD → OD+ + H and OH+ + D ↔ OD+ + H reactions that can occur in diffuse ISM. Reactive rate constants have been obtained from exact state-to-state quantum wave packet calculations for temperatures ranging from 10 to 1000 K. The new theoretical data are validated through a detailed comparison with available experimental data. The formation of OD+ is found to be less efficient than that of OH+. As a first application, the OD+/OH+ abundance ratio in ISM has been evaluated from a simple astrochemical model, and we found that this ratio can be larger than D/H abundance ratio only at low temperatures. These calculations may help in an astrochemical search of OD+ in cold ISM.

Franck-Condon simulations of transition-state spectra for the OH + H2O and OD + D2O reactions.

We present the results of quantum wave packet calculations performed to analyze the experimental transition-state spectra for the OH + H2O and OD + D2O reactions based on photodetachment of the H3O2- and D3O2- anions. We used a reduced-dimensionality model in which four normal-mode coordinates were considered for the neutral transition state. High-level ab initio potential energy surfaces were used for both the neutral and anionic states. The calculated spectra were found to be in reasonable agreement with the experimental spectra. The present study confirms that the vibrational progression observed experimentally is associated with the antisymmetric motion of the transferred H/D atom. We also found that the O-O stretching motion plays an important role in the transition-state dynamics. The influence of vibrational excitation of the H3O2- and D3O2- anions on the photodetachment spectra was also investigated.

Quantum dynamics analysis of transition-state spectrum for the SH + H2S → H2S + SH reaction.

We present the results of quantum wave packet calculations analyzing the experimental transition-state spectrum for the SH + H2S hydrogen transfer reaction based on photodetachment of the H3S2- anion. We used a reduced-dimensionality model in which four normal-mode coordinates were considered for the dynamics of the neutral transition state. The four-dimensional potential energy surfaces for the anionic and neutral states were constructed using four different levels of theory, namely, MP2, B3LYP, CAM-B3LYP, and LC-BLYP, with the aug-cc-pVDZ basis set. The spectrum calculated using the scaled MP2 potential energy surface was in reasonable agreement with the experimental spectrum. The present theoretical study confirms that the vibrational progression observed experimentally is associated with the antisymmetric motion of the transferred hydrogen atom. We also found that the S-S stretching motion plays an important role in the transition-state dynamics.

Quantum Dynamics Calculations of Na (32S, 32P) + HF → NaF + H Reactions.

The dynamics of the reactive scatterings of the ground (Na(3S)) and first excited (Na(3P)) state sodium atoms from hydrogen fluoride (HF) molecules is investigated by performing comprehensive Coriolis-coupled quantum wave packet calculations on the recent ab initio potential energy surface (PES). In the Na(3S) + HF reaction, the nonadiabatic effect is found to be negligibly small, and the reactivity is significantly promoted by the initial vibrational excitations being in line with the available experimental result. Excellent quantitative agreement between theory and experiment is also achieved for the initial state specified integral cross sections and rate constants for v ≥ 3 vibrational states. However, the calculated rate constant for v = 2 significantly underestimates the experimental result. The possible cause for the disagreement is discussed in detail. For the Na(3P) + HF scattering, which can lead to the formation of either the ground state NaF + H product or Na(3S) + HF reactant via the harpooning process, the calculated result for the integral cross section shows excellent agreement with the available experimental result indicating the reasonable accuracy of the interstate coupling term of the employed PES.

New diabatic potential energy surfaces of the NaH2 system and dynamics studies for the Na(3p)\u2009+\u2009H2\u2009\u2192\u2009NaH\u2009+\u2009H reaction

The Na(3p) + H2(X1Σg+) → NaH(X1Σ+) + H(2S) reaction plays an important role in the field of diabatic reaction dynamics. A set of new diabatic potential energy surfaces (PESs) of the NaH2 system are structured, which include the diabatic coupling between the lowest two adiabatic states. The electronic structure calculations are performed on the multi-reference configuration interaction level with the cc-pwCVQZ and aug-cc-PVQZ basis sets for Na and H atoms. 32402 geometries are chosen to construct the diabatic data by a unitary transformation based on the molecular property method. The diabatic matrix elements of {{boldsymbol{V}}}_{{bf{11}}}^{{boldsymbol{d}}}, {{boldsymbol{V}}}_{{bf{22}}}^{{boldsymbol{d}}} and {{boldsymbol{V}}}_{{bf{12}}}^{{boldsymbol{d}}} ({{boldsymbol{V}}}_{{bf{21}}}^{{boldsymbol{d}}}) are fitted by the artificial neural network model. The spectroscopic constants of diatoms obtained from the present PESs are consistent with the experimental data. The topographical and intersection characteristics of the {{boldsymbol{V}}}_{{bf{11}}}^{{boldsymbol{d}}} and {{boldsymbol{V}}}_{{bf{22}}}^{{boldsymbol{d}}} surfaces are discussed. Based on the new PESs, the time-dependent quantum wave packet calculations are carried out to study the reaction mechanism of the title reaction in detail.

Investigation of coriolis coupling effect on the ND + D reaction

We present time dependent quantum wave packet calculations for the NDa1Δ+D'2S reaction on the modified NH2A∼2A1 potential energy surface using the real wave packet and flux analysis methods. Initial-state-resolved reaction probabilities, cross sections and rate constants were obtained taking into account the Coriolis Coupling (CC). The significance of including the CC quantum scattering calculations has been revealed by the comparison between the CC and the Centrifugal Sudden (CS) approximation calculation. The calculated thermal reaction rate constant is in a good agreement with the available experimental data and semiclassical results.

Accuracy of trajectory surface-hopping methods: Test for a two-dimensional model of the photodissociation of phenol.

Trajectory surface hopping (TSH) methods have been widely used for the study of nonadiabatic molecular dynamics. In the present work, the accuracy of two TSH algorithms, Tully's fewest switching algorithm and an algorithm based on the Landau-Zener formula, has been critically evaluated in comparison with exact nonadiabatic quantum dynamics calculations for a model of the photoinduced hydrogen-atom dissociation reaction in phenol. The model consists of three electronic states (S0, 1ππ*, 1πσ*) and two nuclear degrees of freedom (the OH stretching coordinate and CCOH dihedral angle) and displays two successive conical intersections (1ππ*/1πσ* and 1πσ*/S0). Considering instantaneous photoexcitation from different vibrational levels of the S0 state to the 1ππ* state, we examined the time-dependent electronic population dynamics as well as the branching ratio of the two dissociation channels. The results of fully converged trajectory calculations are compared with the results of exact quantum wave-packet calculations. It is found that both TSH algorithms describe the dynamics at the 1πσ*/S0 conical intersection, which is accessed with high excess energy, with good accuracy. The 1ππ*/1πσ* conical intersection, on the other hand, is accessed with little excess energy so tunneling effects as well as wave-packet interference effects which cannot be reproduced with classical trajectory calculations become relevant. Overall, the performance of the fewest-switching and Landau-Zener surface-hopping algorithms for the photodissociation of phenol is very similar. The populations of the adiabatic S1 and S2 states are found to exhibit fast oscillations which reflect nonadiabatic electronic transitions driven by coherent dynamics in the OH stretching mode. These electronic population oscillations are qualitatively reproduced by both TSH algorithms.

A time-dependent quantum dynamical study of the C+(2P) + H2(D2,HD) → CH+(CD+) + H(D) reaction

We present time-dependent quantum wave packet calculations for the C+(2P)+H2(D2,HD)→CH+(CD+)+H(D) reactions on the ground 12A′ potential energy surface developed by Li et al. (2015). The reaction probabilities, the integral cross sections and the thermal rate constants were obtained. The calculated thresholds of title reactions agree well with the thermochemical endothermicities. Moreover, the calculated thermal rate constant of C++H2 reaction agrees well with experimental data, however, smaller than the experimental data for the C++HD and C++D2 reactions.

A global potential energy surface and time‐dependent quantum wave packet calculation of Au + H2 reaction

AbstractA global potential energy surface (PES) corresponding to the ground state of AuH2 system has been constructed based on 22 853 ab initio energies calculated by the multireference configuration interaction method with a Davidson correction. The neural network method is used to fit the PES, and the root mean square error is only 1.87 meV. The topographical features of the novel global PES are compared with previous PES which is constructed by Zanchet et al. (Zanchet PES). The global minimum energy reaction paths on the two PESs both have a well and a barrier. Relative to the Au + H2 reactants, the energy of well is 0.316 eV on the new PES, which is 0.421 eV deeper than Zanchet PES. The calculation of Au(2S) + H2(X1Σg+) → AuH(X1Σ+) + H(2S) dynamical reaction is carried out on new PES, by the time‐dependent quantum wave packet method (TDWP) with second order split operator. The reaction probabilities, integral cross‐sections (ICSs) and differential cross‐sections are obtained from the dynamics calculation. The threshold in the reaction is about 1.46 eV, which is 0.07 eV smaller than Zanchet PES due to the different endothermic energies on the two PESs. At low collision energy (&lt;2.3 eV), the total ICS is larger than the result obtained on Zanchet PES, which can be attributed to the difference of the wells and endothermic energies.

The Photodissociation of HCN and HNC: Effects on the HNC/HCN Abundance Ratio in the Interstellar Medium.

The impact of the photodissociation of HCN and HNC isomers is analyzed in different astrophysical environments. For this purpose, the individual photodissociation cross section of HCN and HNC isomers have been calculated in the 7-13.6 eV photon energy range for a temperature of 10 K. These calculations are based on the ab initio calculation of three-dimensional adiabatic potential energy surfaces of the 21 lower electronic states. The cross sections are then obtained using a quantum wave packet calculation of the rotational transitions needed to simulate a rotational temperature of 10 K. The cross section calculated for HCN shows significant differences with respect to the experimental one, and this is attributed to the need of considering non-adiabatic transitions. Ratios between the photodissociation rates of HCN and HNC under different ultraviolet radiation fields have been computed by renormalizing the rates to the experimental one. It is found that HNC is photodissociated faster than HCN by a factor of 2.2, for the local interstellar radiation field, and 9.2, for the solar radiation field at 1 au. We conclude that to properly describe the HNC/HCN abundance ratio in astronomical environments illuminated by an intense ultraviolet radiation field it is necessary to use different photodissociation rates for each of the two isomers, obtained by integrating the product of the photodissociation cross sections and ultraviolet radiation field over the relevant wavelength range.

Differential Cross Sections for the H + D2 → HD(v′ = 3, j′ = 4–10) + D Reaction above the Conical Intersection

We report rovibrationally selected differential cross sections (DCSs) of the benchmark reaction H + D2 → HD(v' = 3, j' = 4-10) + D at a collision energy of 3.26 eV, which exceeds the conical intersection of the H3 potential energy surface at 2.74 eV. We use the PHOTOLOC technique in which a fluorine excimer laser at 157.64 nm photodissociates hydrogen bromide (HBr) molecules to generate fast H atoms and the HD product is detected in a state-specific manner by resonance-enhanced multiphoton ionization. Fully converged quantum wave packet calculations were performed for this reaction at this high collision energy without inclusion of the geometric phase (GP) effect, which takes into account coupling to the first excited state of the H3 potential energy surface. Multimodal structures can be observed in most of the DCSs up to j' = 10, which is predicted by theory and also well-reproduced by experiment. The theoretically calculated DCSs are in good overall agreement with the experimental measurements, which indicates that the GP effect is not large enough that its existence can be verified experimentally at this collision energy.

Communication: Creation of molecular vibrational motions via the rotation-vibration coupling.

Building on recent advances in the rotational excitation of molecules, we show how the effect of rotation-vibration coupling can be switched on in a controlled manner and how this coupling unfolds in real time after a pure rotational excitation. We present the first examination of the vibrational motions which can be induced via the rotation-vibration coupling after a pulsed rotational excitation. A time-dependent quantum wave packet calculation for the HF molecule shows how a slow (compared to the vibrational period) rotational excitation leads to a smooth increase in the average bond length whereas a fast rotational excitation leads to a non-stationary vibrational motion. As a result, under field-free postpulse conditions, either a stretched stationary bond or a vibrating bond can be created due to the coupling between the rotational and vibrational degrees of freedom. The latter corresponds to a laser-induced breakdown of the adiabatic approximation for rotation-vibration coupling.

Quantum mechanical calculations of state-to-state cross sections and rate constants for the F + DCl → Cl + DF reaction.

We present accurate state-to-state quantum wave packet calculations of integral cross sections and rate constants for the title reaction. Calculations are carried out on the best available ground 1(2)A' global adiabatic potential energy surface of Deskevich et al. [J. Chem. Phys. 124, 224303 (2006)]. Converged state-to-state reaction cross sections have been calculated for collision energies up to 0.5 eV and different initial rotational and vibrational excitations, DCl(v = 0, j = 0 - 1; v = 1, j = 0). Also, initial-state resolved rate constants of the title reaction have been calculated in a temperature range of 100-400 K. It is found that the initial rotational excitation of the DCl molecule does not enhance reactivity, in contract to the reaction with the isotopologue HCl in which initial rotational excitation produces an important enhancement. These differences between the isotopologue reactions are analyzed in detail and attributed to the presence of resonances for HCl(v = 0, j), absent in the case of DCl(v = 0, j). For vibrational excited DCl(v = 1, j), however, the reaction cross section increases noticeably, what is also explained by another resonance.

F+DClCl+DF REAKSİYONU İÇİN DALGA PAKETİ METODU KULLANILARAK BAĞ DURUMLARININ VE BİREYSEL KUANTUM SEVİYELERİ ARASINDAKİ SAÇILMALARIN HESAPLANMASI

Accurate state-to-state quantum wave packet calculations of integral cross sections for the title reaction are presented. Calculations are carried out on the best available ground 12A' global adiabatic potential energy surface of Deskevich et. al.[1]. Converged state-to-state wave packet reaction cross sections with the DCl (v=0, j=0-1; v=1, j=0) reagent have been calculated for the collision energy range from threshold up to 0.5 eV. Accurate product vibrational and rotational distributions of cross sections have been calculated at selected collision energies. State-to-state and total initial-state resolved rate constants of the title reaction have been calculated in a temperature range of 100-300 K. The present accurate calculations at v=0, j=0, J=0 show noticeable differences with previous calculations for the F+HCl reaction. Assuming the reaction coordinate in the F-Cl distance and to estimate the zero point energy in the orthogonal coordinate we have calculated the bound states along the reaction path for frozen F-Cl distance to interpret the results.

Quantum dynamics study of H + DBr and D + HBr reaction.

Time-dependent quantum wave packet calculations have been performed for the H + DBr and D + HBr reaction using the recent diabatic potential energy surfaces. Reaction probabilities, integral cross sections, and rate constants are obtained. The results show that the isotopic effects have an influence on the nonadiabatic effect which is generally inversely proportional to the atom mass. The calculated rate constants are in good overall agreement with experimental values, indicating that the ab initio surfaces are accurate to describe the isotopic effects.

Time-dependent quantum wave packet and quasiclassical trajectory studies of the Au(2S) + H2(X1∑+g) → AuH(X1∑+g) + H(2S) reaction

The time-dependent quantum wave packet (TDWP) and quasiclassical trajectory calculations (QCT) are carried out for the Au(2S) + H2(X1∑+g) → AuH(X1∑+g) + H(2S) reaction on a global potential energy surface. The reaction probabilities at a series of J values, integral cross sections (ICSs) and differential cross sections of the title reaction are calculated by the TDWP method. For reaction probabilities, there are a mass of sharp oscillations at low collision energy, which can be attributed to resonances supported by the potential well. Due to the endothermicity of the title reaction, the total ICS shows a threshold about 1.53 eV. In order to further investigate the reactive mechanism, the lifetime of complex is calculated by QCT method. At the low collision energy, most intermediate complexes are long lived, which implies that the reaction is governed by indirect reactive mechanism. With the collision energy increasing, the direct reactive mechanism occupies the dominant position. Due to the change of the reactive mechanism, the angular distribution shifts toward the forward direction with collision energy increasing. The isotopic variant, Au + D2→AuD + D reaction, is also calculated by TDWP method. The calculated reaction probabilities and ICSs show that the isotope effect reduces the reactivity.

Dynamical properties of S(3P) + HD reaction on 13A″state and their quantum wavepacket calculation

The time‐dependent wavepacket method is used to study the reaction dynamics of S(3P) + HD (v = 0, 1, 2) on the adiabatic 13A″ potential energy surface constructed by Han and coworkers [J. Chem. Phys. 2012, 136, 094308]. The reaction probabilities and integral cross sections as a function of collision energy are obtained and discussed. The results calculated by using the CC and the CS approximation have been compared, which suggests that for this direct abstraction reaction, the cheaper CS approximation calculation is valid enough in the quantum calculation. The investigation also shows that the reaction probabilities and integral cross sections tend to increase with collision energy. By analyzing the v‐dependent behavior of the integral cross sections, the significant effect of the vibrational excitation of HD is found. Also found in the calculation is a significant resonance feature in the reaction probabilities versus collision energy. © 2014 Wiley Periodicals, Inc.

Control of electron localization to isolate and enhance molecular harmonic plateau in asymmetric HeH2+ system

Abstract High-order harmonic generation from the asymmetric molecular ion HeH2+ exposed to intense laser fields was investigated by quantum wave packet calculations in which the initial wave packet of HeH2+ was prepared in the first excited 2 p σ state. The calculated molecular harmonic plateau at low frequencies was effectively isolated and enhanced by adjusting the carrier-envelope phase (CEP) of the laser field. Furthermore, double-well model, time-dependent electronic density, electronic state population, and time-frequency analyses were presented to explain the underlying mechanism of the efficient isolated molecular plateau. By taking advantage of the CEP effect to control the electronic dynamics, this isolated molecular plateau can be used to generate high-intensity single attosecond pulses.