Triatomic Systems Research Articles

Ultracold charged atom-dimer collisions: State-selective charge exchange and three-body recombination

Based on an accurate determination of the potential energy surfaces of Rb3+ correlated to its first asymptotic limit Rb++Rb(5s)+Rb(5s), we identify the presence of intersections of a pair of singlet and triplet surfaces over all interparticle distances, leading to Jahn-Teller (JT) couplings. We elaborate scenarios for charge exchange between ultracold charged atom-dimer complex (Rb+Rb2+ or Rb++Rb2), predicting a strong selectivity on the preparation of the initial state of the dimer. We also demonstrate that the JT couplings must drive the three-body recombination (TBR) of Rb+, Rb, and Rb at ultracold energies. Using the current analysis, we provide a consistent picture of the TBR experiments performed in ion-atom hybrid Rb samples. We also demonstrate the presence of JT coupling as a general phenomenon in the singly charged homonuclear alkali triatomic systems. Published by the American Physical Society 2024

New SiS destruction and formation routes via neutral-neutral reactions and their fundamental role in interstellar clouds at low- and high-metallicity values

Context. Among the silicon-bearing species discovered in the interstellar medium, SiS and SiO stand out as key tracers due to their distinct chemistry and variable abundances in interstellar and circumstellar environments. Nevertheless, while the origins of SiO are well documented, the SiS chemistry remains relatively unexplored. Aims. Our objective is to enhance the network of Si- and S-bearing chemical reactions for a gas-grain model in molecular clouds, encompassing both low and high metallicities. To achieve this, we calculated the energies and rate coefficients for six neutral atom-diatom reactions involved in the SiCS triatomic system, with a special focus on the C+SiS and S+SiC collisions. Methods. We employed the coupled-cluster method with single and double substitutions and a perturbative treatment of triple substitutions (CCSD(T)) refined at the explicitly correlated CCSD(T)-F12 level. With these computational results in conjunction with supplementary data from the literature, we construct an extended network of neutral-neutral chemical reactions involving Si- and S-bearing molecules. To assess the impact of these chemical reactions, we performed time-dependent models employing the Nautilus gas-grain code, setting the gas temperature to 10 K and the H2 density to 2 × 104 cm−3. The models considered two initial abundance scenarios, corresponding to low- and high-metallicity levels. Abundances were computed using both the default chemical network and the constrained network, enriched with newly calculated reactions. Results. The temperature dependence for the reactions involving SiS were modelled to the k(T) = α (T/300)β exp (−γ/T) expression, and the coefficients are provided for the first time. The high-metallicity models significantly boost the SiS production, resulting in abundances nearly four orders of magnitude higher compared to low-metallicity models. Higher initial abundances of C, S, and Si, roughly ~2, 190, and 210 times higher, respectively, contribute to this. Around the age of 103 yr, destruction mechanisms become relevant, impacting the abundance of SiS. The proposed production reaction S + SiC → C + SiS, mitigates these effects in later stages. By expanding the gas reaction network using a high-metallicity model, we derived estimates for the abundances of observed interstellar molecules, including SiO, SO, and SO2. Conclusions. We demonstrate the significance of both SiC+S and C+SiS channels in the SiS chemistry. Notably, the inclusion of neutral-neutral mechanisms, particularly via Si+HS and S+SiC channels, played a pivotal role in determining SiS abundance. These mechanisms carry a significance level on a par with that of the well-known and fast ion-neutral reactions.

Wavelength-Dependent Dynamics of the O(1D2) Channel in the 1Δu State Photodissociation of CO2.

The wavelength-dependent dynamics of the O(1D2) channel, formed by photoexcitation of CO2 to the 1Δu state at 143.53-153.03 nm, is investigated by using the time-sliced velocity-mapped ion imaging method. The measured ionic peaks of the O(1D2) images are analyzed to determine the total kinetic energy release (TKER) spectra and image anisotropy parameters. The structures observed in the TKER spectra can be directly assigned to the ro-vibrational state distributions of the counter CO photofragments. Compared to those observed at 157 and 155 nm, the highly rotationally excited CO photofragments still obviously appear in v = 0 and 1, but the fraction of rotational excitations is significantly reduced. Conversely, the CO photofragments exhibit substantially higher vibrational excitations, implying that the nearly linear 21A' state also contributes to dissociation in addition to the bend configuration. The image anisotropy parameters display an extremely slow decreasing trend with an increase of the CO ro-vibrational state besides those for the highest ro-vibrationally excited CO photofragments. Nevertheless, the nonaxial recoil effect, suggested in previous photodissociation studies of CO2 and other triatomic molecular systems, is still appropriate to explain the observations of internal energy dependences of image anisotropy parameters.

Electronic Structure and Ligand Effects on the Activation and Cleavage of N2 on a Molybdenum Center.

Dinitrogen fixation under ambient conditions remains a challenge in the field of catalytic chemistry due to the inertness of N2. Nitrogenases and heterogeneous solid catalysts have displayed remarkable performance in the catalytic conversion of dinitrogen to ammonia. By introduction of molybdenum centers in molecular complexes, one of the most azophilic metals of the transitional metal series, moderate ammonia yields have been attained. Here, we present a combined multiconfigurational/density functional theory study that addresses how ligand fields of different strengths affect the binding and activation of dinitrogen on molybdenum atoms. First, we explored with MRCI computations the diatomic Mo-N and triatomic Mo-N2 molecular systems. Then, we performed a systematic examination on the stabilization effects introduced by external NH3 ligands, before we explore model neutral and charged complexes with different types of ligands (H2O, NH3, and PH3) and their consequences on the N2 binding and activation.

Calculation of the local environment of a barium monofluoride molecule in a neon matrix

ABSTRACT The local environment of a barium monofluoride (BaF) molecule embedded in a neon matrix is studied theoretically. The energy of the BaF-Ne triatomic system is calculated with a scalar relativistic Hamiltonian, using coupled-cluster theory at the CCSD(T) level for 1625 positions of the Ne atom relative to the BaF molecule. The calculations are repeated with increasing basis sets (from double to quintuple zeta), and are extrapolated to estimate the complete-basis-set limit. Using the potential obtained from these calculations, it is determined that substituting a BaF molecule for ten Ne atoms is favoured compared to substitutions for other numbers of Ne atoms. The equilibrium position and orientation of the BaF molecule and the displacement of its nearby Ne neighbours are determined. The potential barriers that prevent the BaF molecule from migrating and rotating are calculated. These barriers are essential for the EDM 3 collaboration, which is using BaF molecules embedded in a noble-gas solid to perform a precision measurement of the electron electric dipole moment.

NeI2 Photofragmentation Dynamics Through Quasiclassical and Semiclassical Studies.

The triatomic system NeI$_2$ has been studied under the consideration the diatom is found in an excited electronic state (B). The vibrational levels $(v=13,\ldots,23)$ are taken into account in this research. For such a study, we use two well-known theoretical procedure: the QCT (Quasi-Classical Trajectories) method, where the classical equations motion for nuclei are solved on a single potential energy surface (PES), unlike the TSH (Trajectory Surface Hopping) method, where they are solved in a bunch of crossed vibrational PES (diabatic representation). We have incorporated the Trajectory Surface Hopping - Fewest Switches (TSH-FS) in order to minimize the number of hoppings, allowing us calculate the probability of hopping between the different PES's, and the kinetic mechanism to track the path followed for the system until dissociation. By using these methods we are able to obtain several observables like the lifetimes, vibrational and rotational energies (I$_2$), dissociation channels, among others. Our results are compared with previous experimental and theoretical work.

Resonantly enhanced interatomic Coulombic electron capture in a system of three atoms

In interatomic Coulombic electron capture, the capture of a free electron at an atomic center is accompanied by the radiationless transfer of the excess energy to a neighboring atom of different species, leading to ionization of the latter. We show that this interatomic process can be strongly enhanced by the presence of an additional third atom, provided the energy of the free-bound capture transition in the first atom is resonant to a dipole-allowed excitation energy in this assisting atom. The relation of the resonantly enhanced three-center electron capture with other processes is discussed, and its dependencies on the incident electron energy and the spatial geometry of the triatomic system are illustrated.

State-to-state reactive dynamics of H+HD→H2+D at 2.20 eV

As the simplest neutral triatomic reaction system, the H+H2 bimolecular reaction and its isotope variants are critically important for understanding elementary chemical reactions at the microscopic level. A high-resolution crossed molecular beams method was used in this work to explore the H+HD→H2+D elementary chemical reaction at a collision energy of 2.20 eV. The product D atoms were detected using the 1+1′ (vacuum ultraviolet and ultraviolet laser) D-atom near-threshold ionization technique. Differential cross sections with vibrational and rotational state resolutions were experimentally acquired, covering the full scattering angular range. Particularly, fast forward oscillations were presented at several rovibrational states, such as v'=0, j'=10 and v'=1, j'=5. Our analysis shows that scattering partial waves close to J=36 mainly contribute to the oscillatory structures. Moreover, the branching ratios of the odd j' and even j' were also derived, revealing that the rotational populations of the H2 (v'=0) co-product strongly depend on the nuclear spin statistics.

Accurate calculation of the interaction of a barium monofluoride molecule with an argon atom: A step towards using matrix isolation of BaF for determining the electron electric dipole moment

Calculations of the BaF–Ar triatomic system are performed with a relativistic Hamiltonian and coupled cluster theory at the CCSD(T) level for 1386 positions of the Ar atom relative to the BaF molecule. Calculations are repeated with increasing basis sets (double-, triple-, quadruple- and quintuple-zeta), and these are extrapolated to estimate the complete-basis-set limit. The resulting energies provide a potential energy for the interaction of an Ar atom with a BaF molecule. A fit is presented that parametrizes this potential. This work is needed for an understanding of the position, modes of motion and energy shifts of BaF isolated in an Ar matrix. This understanding will guide the EDM3 collaboration in its pursuit of a precision measurement of the electron electric dipole moment using BaF isolated in a cryogenic Ar matrix.

Theoretical Study of Weakly-Bound Triatomic Systems with Discrete Variable Representation

Theoretical Study of Weakly-Bound Triatomic Systems with Discrete Variable Representation

Multilayer Multiconfiguration Time-Dependent Hartree Study on the Mode-/Bond-Specific Quantum Dynamics of Water Dissociation on Cu(111).

In this work, full-dimensional (9D) quantum dynamics calculations on mode-/bond-specific surface scattering of a water molecule on a copper (111) rigid surface are performed through the multilayer multiconfiguration time-dependent Hartree (ML-MCTDH) method. To easily perform the ML-MCTDH calculations on such a triatomic molecule-surface system, we first choose specific Jacobi coordinates as a set of coordinates of water. Next, to efficiently perform the 9D ML-MCTDH wavepacket propagation, the potential energy surface is transferred to a canonical polyadic decomposition form with the aid of a Monte Carlo-based method. Excitation-specific dissociation probabilities of H2O on Cu(111) are computed, and mode-/bond-specific dynamics are demonstrated by comparison with a probability curve computed for a water molecule in the ground state. The dependence of the dissociation probability of the initial state of H2O is studied, and it is found that the excitation-specific dissociation probabilities can be divided into three groups. We find that the vibrationally excited states enhance the dissociation reactivity of H2O, while the rotationally excited states hardly influence it.

Deep learning and high harmonic generation

Using machine learning, we explore the utility of various deep neural networks when applied to high harmonic generation scenarios. First, we train the neural networks to predict the time-dependent dipoles and spectra of high harmonic emission from reduced-dimensionality models of di- and triatomic systems based on sets of randomly generated parameters (laser pulse intensity, internuclear distance, and molecular orientation). These networks, once trained, are useful tools to rapidly simulate the high harmonic spectra of our systems. Similarly, we have trained the neural networks to solve the inverse problem—to determine the molecular parameters based on high harmonic spectra or dipole acceleration data. The latter types of networks could then be used as spectroscopic tools to invert high harmonic spectra in order to recover the underlying physical parameters of a system. Next, we demonstrate that transfer learning can be applied to our networks to expand the range of applicability of the networks with only a small number of new test cases added to our training sets. Finally, we demonstrate neural networks that can be used to classify molecules by type: di- or triatomic, symmetric or asymmetric. With outlooks toward training with experimental data, these neural network topologies offer a novel set of spectroscopic tools that could be incorporated into high harmonic generation experiments.

Quantum Inelastic Scattering of ArHAr+, HeHHe+, and NeHNe+ with He on New Potential Energy Surfaces

The recent interstellar detections of ArH+ and HeH+ have increased the interest in noble molecules. In this work, we develop potential energy surfaces (PESs) at a high level of theory for the HeHHe+ + He, ArHAr+ + He, and NeHNe+ + He complexes and study the collision dynamics. A large number of ab initio energies are computed at the coupled-cluster with single, double, and perturbative triple excitations level of theory for the systems. A grid of energies at the complete basis set limit is fitted to an analytical function for each complex. These PESs are then employed in close-coupling calculations at low collision energies. The rotational state-to-state rate coefficients of HeHHe+ by collision He are compared with previous studies, and an excellent agreement is found. Furthermore, the available quenching rate coefficients for ArH+, HeH+, and NeH+, by He, are compared with those computed in this work, and the rotational de-excitations of the diatoms are more efficient than with the triatomic systems. Finally, a set of rate coefficients for ArHAr+ + He, HeHHe+ + He, and NeHNe+ + He at low temperatures is reported.

Accurate Adiabatic and Diabatic Potential Energy Surfaces for the Reaction of He + H2.

The accurate adiabatic and diabatic potential energy surfaces, which are for the two lowest states of He + H2, are presented in this study. The Molpro 2012 software package is used, and the large basis sets (aug-cc-pV5Z) are selected. The high-level MCSCF/MRCI method is employed to calculate the adiabatic potential energy points of the title reaction system. The triatomic reaction system is described by Jacobi coordinates, and the adiabatic potential energy surfaces are fitted accurately using the B-spline method. The equilibrium structures and electronic energies for the H2 are provided, and the corresponding different levels of vibrational energies of the ground state are deduced. To better express the diabatic process of the whole reaction, avoid crossing points being calculated and conical intersection also being optimized. Meanwhile, the diabatic potential energy surfaces of the reaction process are constructed. This study will be helpful for the analysis of histopathology and for the study in biological and medical mechanisms.

Design of laser pulse to enhance the photo-dissociation of a tri-atomic molecular system using optimal control theory based adaptive simulated annealing technique

In this communication, we design and optimize laser pulses to enhance the dissociation of a tri-atomic molecule using optimal control theory based adaptive simulated annealing technique. ClCN is chosen as tri-atomic molecular system as molecules containing fluorine and chlorine atoms are involved in the depletion of ozone layer and also dissociative electron attachment is possible. Fourier Grid Hamiltonian based 2D mean field methodology has been used for numerical calculations. We find an effective laser pulse by combining polychromatic Gaussian pulses and polychromatic linear pulses with different frequencies and different field intensities.

M-CHIPR: A Mathematica program for constructing multi-state coupled adiabatic potential energy functions in triatomic molecule using many body partitioning approach

The permutationally invariant combined hyperbolic inverse power representation (CHIPR) polynomial expansion in terms of hyperbolic secant basis proves to be an efficient model in describing the multi state coupled potential energy surface (MSCPES) and this fact was tested on the O2H+ triatomic ion and its diatomic sub units upon dissociation with an unmatchable accuracy of fitting in comparison with the previous works (below 1cm−1 in the case of diatomic function and below 300cm−1 in the case of triatomic function). In general, this model is capable of modeling A3 (H3, O3 etc.) and ABC (OCS, HCO+ etc.) triatomic system in addition to the A2B (O2H+) system. This paper presents a Mathematica notebook (M-CHIPR.nb file) to perform the fitting of di and triatomic potentials in a user friendly manner with proper explanations written along side wherever required in the .nb file supplied. The advantage of this code is that the computing clusters are not required to use it and can be run in normal pc with good processor and memory, apart from its numerical accuracy and the system independent consistency over the similar programs written in other languages. Program summaryProgram title: M-CHIPRCPC Library link to program files:https://doi.org/10.17632/4mbydkzyts.1Licensing provisions: GPLv3Programming language: Wolfram Mathematica version12 or higherNature of problem: Finding an multi-variable Mathematica combined hyperbolic inverse power representation (M-CHIPR) function to describe a multi state coupled potential energy surface for a typical diatomic and triatomic molecule via extensive nonlinear regression method involving hundreds of optimizable variables with minimal fitting error with respect to the raw data points.Solution method: Default Mathematica implementation of nonlinear least square fitting of ab initio points to obtain a well optimized model function having ability to accurately predicting the data behavior.Additional comments including restrictions and unusual features: The entire work was tested on Apple Mac pc with Intel i7 processor having 4 cores. The version of Mathematica is 12 and therefore, the users are advised to test the supplied notebook with the same version and beyond to avoid incompatibility issues.

Quantum mechanical double slit for molecular scattering.

Interference observed in a double-slit experiment most conclusively demonstrates the wave properties of particles. We construct a quantum mechanical double-slit interferometer by rovibrationally exciting molecular deuterium (D2) in a biaxial (v = 2, j = 2) state using Stark-induced adiabatic Raman passage, where v and j represent the vibrational and rotational quantum numbers, respectively. In D2 (v = 2, j = 2) → D2 (v = 2, j′ = 0) rotational relaxation via a cold collision with ground state helium, the two coherently coupled bond axis orientations in the biaxial state act as two slits that generate two indistinguishable quantum mechanical pathways connecting initial and final states of the colliding system. The interference disappears when we decouple the two orientations of the bond axis by separately constructing the uniaxial states of D2, unequivocally establishing the double-slit action of the biaxial state. This double slit opens new possibilities in the coherent control of molecular collisions.

SpectrumSDT: A program for parallel calculation of coupled rotational-vibrational energies and lifetimes of bound states and scattering resonances in triatomic systems

We present SpectrumSDT – a program for calculations of energies and lifetimes of bound rotational-vibrational states below and scattering resonances above the dissociation threshold on a global potential energy surface of a triatomic system, which may include stable molecules, weekly-bound van-der-Waals complexes, and unbound atom + diatom scattering systems. Large-amplitude vibrational motion is treated explicitly using hyper-spherical coordinates. Three options for the rotational-vibrational interaction are supported: uncoupled (symmetric top rotor), partially coupled (to include interaction between several nearest states only) and full-coupled (vibrating asymmetric-top rotor). In addition to energies and lifetimes, SpectrumSDT is able to integrate ro-vibrational wave functions over the user-defined regions of potential energy surface, which helps to classify these states. In this release of the code, SpectrumSDT is limited to ABA-type molecules with wave functions that do not extend into the regions near Eckart singularities. Program summaryProgram title: SpectrumSDTCPC Library link to program files:https://doi.org/10.17632/9gftxjs4yk.1Developer's repository link:https://github.com/IgorGayday/SpectrumSDTLicensing provisions: GNU General Public License 3 (GPL)Programming language: FortranNature of problem: Calculations of energies and lifetimes of bound rotational-vibrational states below and scattering resonances above the dissociation threshold on a global potential energy surface of a triatomic system, which may include stable molecules, weekly-bound van-der-Waals complexes, and unbound atom + diatom scattering systems.Solution method: A Hamiltonian matrix is built in APH coordinates using an optimal 2D basis set, adjusted for a given problem. A complex absorbing potential (CAP) is added to define a boundary condition for calculation of scattering resonances above the dissociation threshold. The eigenstates of the Hamiltonain matrix are found using a state-of-the-art iterative eigensolver.Restrictions: The present version is restricted to ABA-molecules and wave functions that do not extend into linear and equilateral triangle configurations.Additional comments including restriction and unusual features: Probabilities and lifetimes of the wave functions can be calculated in user-defined regions on the PES, which allows to analyze their localization properties (i.e. automatic isotopomer assignment) and obtain channel-specific lifetimes for scattering resonances.

Theoretical Study of Weakly-Bound Triatomic Systems with Faddeev Equations in the Total Orbital Momentum Representation

Theoretical Study of Weakly-Bound Triatomic Systems with Faddeev Equations in the Total Orbital Momentum Representation

Singlet-triplet interaction of the adiabatic terms [formula omitted] and [formula omitted] in the linear triatomic molecules

The paper introduces the 4x4 vibronic matrix that describes singlet–triplet interaction of adiabatic terms 1Σ+ and 3Σ+ via deformation π-modes of the linear triatomic system. Our analysis takes into account spin-orbital coupling in ab initio Breit-Pauli form in the framework of two-electronic model. It is shown that the symmetry operators of electronic Hamiltonian include both space operations (acting on electronic coordinates) and matrix operations (acting on electronic spins). Eigenvalues of vibronic matrix (i.e. potential energy surfaces) are invariants of the molecular symmetry group C∞ν. The 4x4 vibronic matrix includes 4 electrostatic parameters and 3 parameters caused by spin-orbital interaction.