http://hdl.handle.net/10366/138663 2026-04-21T12:06:28Z http://hdl.handle.net/10366/170285 [EN]We present MADWAVE3, a FORTRAN90 code designed for quantum time-dependent wave packet propagation in triatomic systems. This program allows the calculation of state-to-state probabilities for inelastic and reactive collisions, as well as photodissociation processes, over one or multiple coupled diabatic electronic states. The code is highly parallelized using MPI and OpenMP. The execution requires the potential energy surfaces of the different electronic states involved, as well as the transition dipole moments for photodissociation processes. The formalism underlying the code is presented in section 2, together with the modular structure of the code. This is followed by the installation procedures and a comprehensive list and explanation of the parameters that control the code, organized within their respective namelists. Finally, a case study is presented, focusing on the prototypical reactive collision H+DH(v, j)→ H2(v′, j′) + D. Both the potential energy surface and the input files required to reproduce the calculation are provided and are available on the repository’s main page. This example is used to study the parallelization speedup of the code. 2025-01-01T00:00:00Z http://hdl.handle.net/10366/170284 [EN]Following the previous study with an extensive range of quantum calculations involving different electronic states of the BN− anion [Dulitz et al., Phys. Scripta 100, 055411 (2025)], we now extend that work by modeling the quantum dynamics of the collision cooling of its rotational states in order to investigate possible paths for bringing this molecular anion down to temperatures of a few Kelvins. This specific ionic system is of direct interest when modeling experiments in cold ion traps where He or Ar atoms can function as the chief buffer gases that drive the anions down to the low trap temperatures. We employ accurate, ab initio calculations of the potential energy surfaces for the title system in its ground electronic state, interacting with either He or Ar atoms. We then obtain a wide range of inelastic cross sections and the ensuing rate coefficients in order to model the quantum kinetics of the time evolution of the cooling steps under different temperature and trap conditions. The results are analyzed and employed to estimate the cooling efficiency paths provided by various trap arrangements for the title anion. The results show that—using either of the two investigated species—the buffer gas cooling process very efficiently brings the anions to their lowest rotational states. These findings are very promising for future applications in the field of anion laser cooling. 2025-01-01T00:00:00Z http://hdl.handle.net/10366/170283 [EN]Context. In diffuse interstellar clouds, the excitation temperature derived from the lowest levels of H+ 3 is systematically lower than that derived from H2. The differences may be attributed to the lack of state-specific formation and destruction rates of H+ 3 , which are needed to thermalize the two species. Aims. In this work, we aim to investigate the possible influence of rotational excitation collisions of H+ 3 with atomic hydrogen on its excitation temperature. Methods. We used a time-independent close-coupling method to calculate the state-to-state rate coefficients, incorporating a very accurate and full-dimensional potential energy surface recently developed for H+ 4 . We take a symmetric top approach to describe a frozen H+ 3 as an equilateral triangle. Results. We derive rotational excitation collision rate coefficients of H+ 3 with atomic hydrogen in a temperature range corresponding to diffuse interstellar conditions up to (J, K, ±) = (7, 6, +) and (J, K, ±) = (6, 4, +) for its ortho and para forms. This allows us to obtain a consistent set of collisional excitation rate coefficients and to improve on a previous study that included speculations regarding these contributions. Conclusions. The new state-specific inelastic H+ 3 + H rate coefficients yield differences of up to 20% in the excitation temperature, and their impact increases with decreasing molecular fraction. We also confirm the impact of chemical state-to-state destruction reactions on the excitation balance of H+ 3 , and that reactive H + H+ 3 collisions are also needed to account for possible further ortho to para transitions. 2025-01-01T00:00:00Z http://hdl.handle.net/10366/170282 [EN]Carbon hydrides play a crucial role in the formation of complex organic molecules in highly UV illuminated regions of the interstellar medium (ISM). The formation of CH+ is the first step in the reactions leading to the formation of various carbon hydrides. CH+ formation is relatively well understood with strong agreement between theoretical and experimental results. However, its destruction by collision with the H atom, at low temperatures of interest in the ISM, is in contrast still not well understood and there is a large discrepancy between theoretical and experimental data [R. Plasil et al., AstroPhys. J., 2011, 737, 1], which are almost an order of magnitude smaller than various classical and quantum mechanical calculations. In this work we have computed and fitted a new set of non-adiabatic potential energy surfaces (PES) for the title system, including the three lower adiabatic states. We then investigate three possible sources of disagreement with the experimental results: non-adiabatic effects from regions near the conical intersections, and rotational and vibrational excitation of the CH+ molecule. We conclude that vibrational excitation of the CH+ plays a major role in reducing the reactivity at low temperatures, and we raise the question of whether vibrational thermalization of the CH+ is not fully achieved in the experiment. Such non-thermalized conditions could explain the decrease of the measured reaction rate constant. 2025-01-01T00:00:00Z http://hdl.handle.net/10366/170280 [EN] We discuss the HCN + H− reaction as a path to the formation of CN−, the smallest cyanopolyyne anion observed in several interstellar environments. We first obtain the new ab initio reactive potential energy surface using a full 5D representation, where only the C–N bond is kept fixed, and discuss the neural network procedure employed to yield an accurate fit for the dynamics. The reaction is then investigated by using a quasi-classical trajectory approach to scan the low-temperature range of the dark molecular clouds where the anion has been sighted. Calculations are extended to room temperature to make a successful comparison with existing experimental data. We further present reduced dimensionality modeling of the reaction as a 2D process within a variational-transition state treatment with the inclusion of long-range forces. The dominant role of such forces in producing large reaction rate coefficients is discussed for both treatments, which yield very similar sizes and behavior of such coefficients from 50 to 300 K. The implications of our results for the interstellar medium formation of the CN− species via this chemical route are discussed, suggesting its greater significance over the radiative electron attachment paths, whose rate coefficients were found by recent calculations to be orders of magnitude smaller. 2024-01-01T00:00:00Z http://hdl.handle.net/10366/170279 [EN]CH+3 , a cornerstone intermediate in interstellar chemistry, has recently been detected for the first time by using the James Webb Space Telescope. The photodissociation of this ion is studied here. Accurate explicitly correlated multi-reference configuration interaction ab initio calculations are done, and full-dimensional potential energy surfaces are developed for the three lower electronic states, with a fundamental invariant neural network method. The photodissociation cross section is calculated using a full-dimensional quantum wave packet method in heliocentric Radau coordinates. The wave packet is represented in angular and radial grids, allowing us to reduce the number of points physically accessible, requiring to push up the spurious states appearing when evaluating the angular kinetic terms, through projection technique. The photodissociation spectra, when employed in astrochemical models to simulate the conditions of the Orion bar, result in a lesser destruction of CH+3 compared to that obtained when utilizing the recommended values in the kinetic database for astrochemistry. 2024-01-01T00:00:00Z http://hdl.handle.net/10366/170278 [EN]The title reaction is studied using a quasi-classical trajectory method for collision energies between 0.1 meV and 10 eV, considering the vibrational excitation of H+ 2 reactant. A new potential energy surface is developed based on a Neural Network many body correction of a triatomics-in-molecules potential, which significantly improves the accuracy of the potential up to energies of 17 eV, higher than in other previous fits. The effect of the fit accuracy and the non-adiabatic transitions on the dynamics are analysed in detail. The reaction cross section for collision energies above 1 eV increases significantly with the increasing of the vibrational excitation of H+ 2 (v′), for values up to v′ = 6. The total reaction cross section (including the double fragmentation channel) obtained for v′ = 6 matches the new experimental results obtained by Savic, Schlemmer and Gerlich [Chem. Phys. Chem. 21 (13), 1429.1435 (2020). doi:10.1002/cphc.v21.13]. The differences among several experimental setups, for collision energies above 1 eV, showing cross sections scattered/dispersed over a rather wide interval, can be explained by the differences in the vibrational excitations obtained in the formation of H+ 2 reactants. On the contrary, for collision energies below 1 eV, the cross section is determined by the long range behaviour of the potential and do not depend strongly on the vibrational state of H+ 2 . In addition in this study, the calculated reaction cross sections are used in a plasma model and compared with previous results. We conclude that the efficiency of the formation of H+ 3 in the plasma is affected by the potential energy surface used. 2023-01-01T00:00:00Z http://hdl.handle.net/10366/170094 [EN]In recent years, machine learning potentials (MLP) for atomistic simulations have attracted a lot of attention in chemistry and materials science. Many new approaches have been developed with the primary aim to transfer the accuracy of electronic structure calculations to large condensed systems containing thousands of atoms. In spite of these advances, the reliability of modern MLPs in reproducing the subtle details of the multi-dimensional potential-energy surface is still difficult to assess for such systems. On the other hand, moderately sized systems enabling the application of tools for thorough and systematic quality-control are nowadays rarely investigated. In this work we use benchmark-quality harmonic and anharmonic vibrational frequencies as a sensitive probe for the validation of high-dimensional neural network potentials. For the case of the formic acid dimer, a frequently studied model system for which stringent spectroscopic data became recently available, we show that high-quality frequencies can be obtained from state-of-the-art calculations in excellent agreement with coupled cluster theory and experimental data. 2022-01-01T00:00:00Z http://hdl.handle.net/10366/170044 [EN]To simulate a 200 nm photoexcitation in cyclobutanone to the n-3s Rydberg state, classical trajectories were excited from a Wigner distribution to the singlet state manifold based on excitation energies and oscillator strenghts. Twelve singlet and twelve triplet states are treated using TD-B3LYP-D3/6-31+G∗∗for the electronic structure and the nuclei are propagated with the Tully Surface Hopping method. Using TD-DFT, we are able to predict the bond cleavage that takes place on the S1 surface as well as the ultrafast deactivation from the Rydberg n-3s state to the nπ∗. After showing that triplet states and higher-lying singlet states do not play any crucial role during the early dynamics (i.e., the first 300 fs), the SA(6)-CASSCF(8,11)/aug-cc-pVDZ method is used as an electronic structure and the outcome of the non-adiabatic dynamic simulations is recomputed. Gas-phase ultrafast electron diffraction (GUED) spectra are computed for both electronic structure methods, showing significantly different results. 2024-01-01T00:00:00Z http://hdl.handle.net/10366/170043 [EN]Molecular rotation, vibration, internal rotation, isomerization, tunneling, intermolecular dynamics of weakly and strongly interacting systems, intra-to-inter-molecular energy transfer, hindered rotation and hindered translation over surfaces are important types of molecular motions. Their fundamen- tally correct and detailed description can be obtained by solving the nuclear Schr¨odinger equation on a potential energy surface. Many of the chemically interesting processes involve quantum nu- clear motions which are ‘delocalized’ over multiple potential energy wells. These ‘large-amplitude’ motions in addition to the high dimensionality of the vibrational problem represent challenges to the current (ro)vibrational methodology. A review of the quantum nuclear motion methodology is provided, current bottlenecks of solving the nuclear Schr¨odinger equation are identified, and solu- tion strategies are reviewed. Technical details, computational results, and analysis of these results in terms of limiting models and spectroscopically relevant concepts are highlighted for selected numerical examples. 2023-01-01T00:00:00Z http://hdl.handle.net/10366/170042 [EN]Curvilinear kinetic energy models are developed for variational nuclear motion computa- tions including the inter- and the low-frequency intra-molecular degrees of freedom of the formic acid dimer. The coupling of the inter- and intra-molecular modes is studied by solv- ing the vibrational Schr¨odinger equation for a series of vibrational models, from two up to ten active vibrational degrees of freedom by selecting various combinations of active modes and constrained coordinate values. Vibrational states, nodal assignment, and infrared vi- brational intensity information is computed using the the full-dimensional potential energy surface (PES) and electric dipole moment surface developed by Qu and Bowman [Phys. Chem. Chem. Phys. 18, 24835 (2016); J. Chem. Phys. 148, 241713 (2018)]. Good results are obtained for several fundamental and combination bands in comparison with with jet-cooled vibrational spectroscopy experiments, but the description of the ν8 and ν9 fundamental vibrations, which are close in energy and have the same symmetry, appears to be problematic. For further progress in comparison with experiment, the potential energy surface, and in particular, its multi-dimensional couplings representation, requires further improvement. 2021-01-01T00:00:00Z http://hdl.handle.net/10366/170041 [EN]The present work intends to join and respond to the excellent and thoroughly documented rovibrational study of X. G. Wang and T. Carrington, Jr. [J. Chem. Phys. 154, 124112 (2021)] that used an approach tailored for floppy dimers with an analytic dimer Hamiltonian and a non-product basis set including Wigner D functions. It is shown in the present work that the GENIUSH black-box-type rovibrational method can approach the performance of the tailor-made computation for the example of the floppy methane-water dimer. Rovibrational transition energies and intensities are obtained in the black-box-type computation with a twice as large basis set and in excellent numerical agreement in comparison with the more efficient tailor-made approach. 2021-01-01T00:00:00Z http://hdl.handle.net/10366/169777 [EN]In this work, we combine theoretical and experimental methods to study the P+(3P)+D2 → PD++D reaction. As a result, the absolute cross section as a function of collision energy is obtained. Ex- perimentally, the cross section is measured using the guided ion beam technique (GIB), where P+ is produced by VUV photons at the SOLEIL synchrotron using PCl3 as a precursor. Theoretically, the cross section is calculated from rst principles. The potential energy surfaces of the three electronic states correlating to the P+(3P) are constructed by tting MRCI points, and reaction dynamics is performed on each of them independently, hence neglecting couplings. The total cross section is then obtained from the weighted contribution of each considered electronic state. Our ndings show a good agreement between the measured and calculated cross sections, with a small discrepancy indicating that spin-orbit and non-adiabatic coupling, not considered in this work, may play a role in this reaction. The results hereafter presented demonstrate that the chemistry of third-row atomic cations with molecular hydrogen is generally unfavoured, unlike their second-row homologues, thus manifesting the existence of boundaries to the use of the so-called chemical analogy (i.e., assuming the same chemical behaviour for elements belonging to the same group) 2026-01-01T00:00:00Z http://hdl.handle.net/10366/169556 [EN]Although formaldehyde, H2CO, has been extensively studied there are still several issues not-well understood, specially regarding its dynamics in the VUV energy range, mainly due to the amount of nonadiabatic effects governing its dynamics. Most of the theoretical work on this molecule has focused on vertical excitation energies of Rydberg and valence states. In contrast to photodissociation processes involving the lowest-lying electronic states below 4.0 eV, there is little known about the photodynamics of the high-lying electronic states of formaldehyde (7-10 eV). One question of particular interest is why the (pi, pi*) electronic state is invisible experimentally even though it corresponds to a strongly dipole-allowed transition. In this work we present a coupled multisurface 2D photodynamics study of formaldehyde along the CO stretching and the symmetric HCH bending motion, using a quantum time-dependent approach. Potential energy curves along all the vibrational normal modes of formaldehyde have been computed using equation-of-motion coupled cluster including single and double excitations with a quadruply augmented basis set. In the case of the CO stretching coordinate, state-averaged complete active space self-consistent field followed by multireference configuration interaction was used for large values of this coordinate. 2D (for the CO stretching coordinate and the HCH angle) and 3D (including the out-of-plane distortion) potential energy surfaces have been computed for several Rydberg and valence states. Several conical intersections (crossings between potential energy surfaces of the same multiplicity) have been characterized and analyzed and a 2D 5 x 5 diabatic model Hamiltonian has been constructed. Based on this Hamiltonian, electronic absorption spectra, adiabatic and diabatic electronic populations and vibrational densities have been obtained and analyzed. The experimental VUV absorption spectrum in the 7-10 eV energy range is well reproduced, including the vibrational structure and the high irregularity in the regime of strong interaction between the (pi, pi*) electronic state and neighboring Rydberg states. 2010-01-01T00:00:00Z http://hdl.handle.net/10366/169555 [EN]An energy-based method is proposed for the diabatization of the OH((2)Pi)+F(P-2)-> O(P-3)+HF((1)Sigma(+)) reaction. It is demonstrated that the diabatic representation obtained is regularized, i.e., the residual derivative couplings do not present singularities at the conical intersections appearing along the reaction path. This method only requires the knowledge of the 1,2 (3)A(') and 1 (3)A(') eigenvalues and does not require any adjustable parameter. Thus, many convergence problems arising in other derivative-based diabatization methods are avoided, and the description of the configuration space along the reaction path is enormously simplified. Three-dimensional coupled diabatic energy surfaces are obtained by an interpolation procedure using approximate to 4000 accurate ab initio points. The angular resolved photodetachment cross sections are obtained in the diabatic and adiabatic representations using a wave packet method. An excellent agreement is obtained with recent experimental data [D. M. Neumark, Phys. Chem. Chem. Phys. 7, 433 (2005)] for high electron kinetic energies where only the triplet electronic states contribute. (c) 2006 American Institute of Physics. 2006-01-01T00:00:00Z http://hdl.handle.net/10366/169554 [EN]A procedure for the transformation from reactant to product Jacobi coordinates is proposed, which is designed for the extraction of state-to-state reaction probabilities using a time-dependent method in a body-fixed frame. The method consists of several steps which involve a negligible extra computational time as compared with the propagation. Several intermediate coordinates are used, in which the efficiency depends on the masses of the atoms involved in the reaction. A detailed study of the relative efficiency of using reactant and product Jacobi coordinates is presented for several systems, and simple arguments are found depending on the masses of the atoms involved in the reaction. It is found that the proposed method is, in general, more efficient than the use of product Jacobi coordinates, specially for nonzero total angular momentum. State-to-state reaction probabilities are obtained for Li+FH -> LiF+H and F+HO -> FH+O collisions for several total angular momenta. (c) 2006 American Institute of Physics. 2006-01-01T00:00:00Z