MTA ELTE Complex Chemical Systems Research Group

Budapest, Hungary

MTA ELTE Complex Chemical Systems Research Group

Budapest, Hungary
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Papp D.,MTA ELTE Complex Chemical Systems Research Group | Sarka J.,MTA ELTE Complex Chemical Systems Research Group | Szidarovszky T.,MTA ELTE Complex Chemical Systems Research Group | Csaszar A.G.,MTA ELTE Complex Chemical Systems Research Group | And 3 more authors.
Physical Chemistry Chemical Physics | Year: 2017

Rotational-vibrational states of the Ar·NO+ cationic complex are computed, below, above, and well above the complex's first dissociation energy, using variational nuclear motion and close-coupling scattering computations. The HSLH potential energy surface used in this study (J. Chem. Phys., 2011, 135, 044312) is characterized by a first dissociation energy of D0 = 887.0 cm-1 and supports 200 bound vibrational states. The bound-state vibrational energies and the corresponding wave functions allow the interpretation of the scarcely available experimental results about the intermonomer vibrational motion of the complex. A very large number of long-lived quasibound combination states of the three vibrational modes, exhibiting a very similar energy-level structure as that of the bound states, are found embedded in the continuum. Additional short-lived resonance states are also identified and their properties are analyzed. © the Owner Societies 2017.


Ajili Y.,University Paris Est Creteil | Trabelsi T.,University Paris Est Creteil | Denis-Alpizar O.,CNRS Institute of Molecular Sciences | Stoecklin T.,CNRS Institute of Molecular Sciences | And 4 more authors.
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2016

The rovibrational eigenenergy set of molecular systems is a key feature needed to understand and model elementary chemical reactions. A unique class of molecular systems, represented by an 4A′′ excited electronic state of the [H,S,N]- system comprising several distinct dipole-bound isomers, is found to contain both bent and linear minima separated by relatively small barriers. Full-dimensional nuclear-motion computations performed in Jacobi coordinates using three-dimensional potential energy surfaces describing the stable isomers and the related transition states yield rovibrational eigenstates located both below and above the barriers. The rovibrational wave functions are well localized, regardless of whether the state's energy is below or above the barriers. We also show that the states preserve the memory of the isomeric forms they "originate from," which is signature of a strong vibrational memory effect above isomerization barriers. © 2016 American Physical Society.


Tobias R.,MTA ELTE Complex Chemical Systems Research Group | Furtenbacher T.,MTA ELTE Complex Chemical Systems Research Group | Csaszar A.G.,MTA ELTE Complex Chemical Systems Research Group
Journal of Quantitative Spectroscopy and Radiative Transfer | Year: 2017

Cycle bases of graph theory are introduced for the analysis of transition data deposited in line-by-line rovibronic spectroscopic databases. The principal advantage of using cycle bases is that outlier transitions -almost always present in spectroscopic databases built from experimental data originating from many different sources- can be detected and identified straightforwardly and automatically. The data available for six water isotopologues, H216O, H217O, H218O, HD16O, HD17O, and HD18O, in the HITRAN2012 and GEISA2015 databases are used to demonstrate the utility of cycle-basis-based outlier-detection approaches. The spectroscopic databases appear to be sufficiently complete so that the great majority of the entries of the minimum cycle basis have the minimum possible length of four. More than 2000 transition conflicts have been identified for the isotopologue H216Oin the HITRAN2012 database, the seven common conflict types are discussed. It is recommended to employ cycle bases, and especially a minimum cycle basis, for the analysis of transitions deposited in high-resolution spectroscopic databases. © 2017 Elsevier Ltd.


Sarka J.,Eötvös Loránd University | Sarka J.,MTA ELTE Complex Chemical Systems Research Group | Csaszar A.G.,Eötvös Loránd University | Csaszar A.G.,MTA ELTE Complex Chemical Systems Research Group | Matyus E.,Eötvös Loránd University
Physical Chemistry Chemical Physics | Year: 2017

Rovibrational states of four dimers formed by the light and the heavy isotopologues of the methane and water molecules are computed using a potential energy surface taken from the literature. The general rovibrational energy-level pattern characteristic to all systems studied is analyzed employing two models of a dimer: the rigidly rotating complex and the coupled system of two rigidly rotating monomers. The rigid-rotor model highlights the presence of rovibrational sequences corresponding to formally negative rotational excitation energies, which is explained in terms of the coupled-rotors picture. © 2017 the Owner Societies.


Sarka J.,Eötvös Loránd University | Sarka J.,MTA ELTE Complex Chemical Systems Research Group | Fabri C.,ETH Zurich | Szidarovszky T.,MTA ELTE Complex Chemical Systems Research Group | And 5 more authors.
Molecular Physics | Year: 2015

One-dimensional (1D) and two-dimensional (2D) models are investigated, which help to understand the unusual rovibrational energy-level structure of the astronomically relevant and chemically interesting astructural molecular ion H+5. Due to the very low hindering barrier characterising the 1D torsion-only vibrational model of H+5, this model yields strongly divergent energy levels. The results obtained using a realistic model for the torsion potential, including the computed (near) degeneracies, can be rationalised in terms of the model with no barrier. Coupling of the torsional motion with a single rotational degree of freedom is also investigated in detail. It is shown how the embedding-dependent rovibrational models yield energy levels that can be rationalised via the 2D vibrational model containing two independent torsions. Insight into the complex rovibrational energy level structure of the models and of H+5 is gained via variational nuclear motion and diffusion Monte Carlo computations and by the analysis of the wavefunctions they provide. The modelling results describing the transition from the zero barrier limit to the large barrier limit should prove to be useful for the important class of molecules and molecular ions that contain two weakly coupled internal rotors. © 2015 Taylor & Francis.


Sarka J.,Eötvös Loránd University | Sarka J.,MTA ELTE Complex Chemical Systems Research Group | Csaszar A.G.,Eötvös Loránd University | Csaszar A.G.,MTA ELTE Complex Chemical Systems Research Group
Journal of Chemical Physics | Year: 2016

Variational nuclear motion computations, employing an exact kinetic energy operator and two different potential energy surfaces, are performed to study the first 60 vibrational states of the molecular ion H5 + ≡ [H2-H-H2]+ and all of its deuterated isotopologues and isotopomers, altogether 12 species. Detailed investigation of the vibrational wavefunctions mostly results in physically intuitive labels not only for the fundamentals but also for the overtone and combination states computed. The torsional motion associated with the left and right diatomics appears to be well separated from the other vibrational degrees of freedom for all species. The unusual structure of the higher-lying bending states and the heavy mixing of the internal motions is partly due to the astructural character of all these molecular ions. The existence of distinct isotopomers in the H5-nD5 +, n = 1-4 cases, in the energy range studied, is confirmed. Two rules determine the stability order of the isotopomers: first, when possible, H prefers to stay in the middle of the ions rather than at the sides, and, second, the isotopomer with a homonuclear diatomic at the side is always lower in energy. The large number of precise vibrational energies of the present study, as well as the detailed assignment of the states, should serve as benchmarks for future studies by more approximate nuclear-motion treatments, such as diffusion Monte Carlo and multiconfiguration time-dependent Hartree. © 2016 Author(s).


Arendas P.,MTA ELTE Complex Chemical Systems Research Group | Arendas P.,Eötvös Loránd University | Furtenbacher T.,MTA ELTE Complex Chemical Systems Research Group | Furtenbacher T.,Eötvös Loránd University | And 2 more authors.
Journal of Mathematical Chemistry | Year: 2016

Spectroscopic networks (SNs), where the vertices are discrete, rovibronic energy levels and the edges are transitions among the levels allowed by quantum mechanics, serve as useful models helping to understand high-resolution spectra of molecular systems. The experimental SNs of the (Formula presented.), and (Formula presented.) molecules, containing a single copy of the known measured and assigned transitions, are investigated via the corresponding network representation matrices, including the Ritz matrix (Formula presented.), the adjacency matrix (Formula presented.), the combinatorial Laplacian matrix (Formula presented.), and the normalized Laplacian matrix (Formula presented.). Using elements of graph (network) theory and the eigenvalue spectra of the matrices mentioned, several interesting results relevant for high-resolution molecular spectroscopy are revealed about the structure of the investigated SNs. For example, as long as the parity selection rule of molecular rovibrational transitions is not violated, the experimental SNs investigated not only contain, with the exception of (Formula presented.), two principal components but they are all bipartite networks, as proven by the symmetry of the eigenvalue spectrum of (Formula presented.) about the origin. Furthermore, the PageRank ordering system is introduced to molecular spectroscopy to identify the most important vertices of SNs. The rankings provided by the degree of the levels and by PageRank may differ significantly; it appears that PageRank provides the more useful ranking. The connectors of relatively dense clusters of the SNs are identified and analysed via spectral clustering techniques based on (Formula presented.) and (Formula presented.). The identification of connectors becomes especially important when judging the true accuracy of the experimental rovibrational energy levels obtained through the Measured Active Rotational-Vibrational Energy Levels (MARVEL) approach, built with the help of the Ritz matrix (Formula presented.). © 2016, Springer International Publishing Switzerland.


Csaszar A.G.,MTA ELTE Complex Chemical Systems Research Group | Csaszar A.G.,Eötvös Loránd University | Furtenbacher T.,MTA ELTE Complex Chemical Systems Research Group | Furtenbacher T.,Eötvös Loránd University
Journal of Physical Chemistry A | Year: 2015

An additive, linear, atom-type-based (ATB) scheme is developed allowing no-cost estimation of zero-point vibrational energies (ZPVE) of neutral, closed-shell molecules in their ground electronic states. The atom types employed correspond to those defined within the MM2 molecular mechanics force field approach. The reference training set of 156 molecules cover chained and branched alkanes, alkenes, cycloalkanes and cycloalkenes, alkynes, alcohols, aldehydes, carboxylic acids, amines, amides, ethers, esters, ketones, benzene derivatives, heterocycles, nucleobases, all the natural amino acids, some dipeptides and sugars, as well as further simple molecules and ones containing several structural units, including several vitamins. A weighted linear least-squares fit of atom-type-based ZPVE increments results in recommended values for the following atoms, with the number of atom types defined in parentheses: H(8), D(1), B(1), C(6), N(7), O(3), F(1), Si(1), P(2), S(3), and Cl(1). The average accuracy of the ATB ZPVEs is considerably better than 1 kcal mol-1, that is, better than chemical accuracy. The proposed ATB scheme could be extended to many more atoms and atom types, following a careful validation procedure; deviation from the MM2 atom types seems to be necessary, especially for third-row elements. © 2015 American Chemical Society.


PubMed | MTA ELTE Complex Chemical Systems Research Group and Eötvös Loránd University
Type: Journal Article | Journal: The journal of physical chemistry. A | Year: 2016

Quantum mechanics builds large-scale graphs (networks): the vertices are the discrete energy levels the quantum system possesses, and the edges are the (quantum-mechanically allowed) transitions. Parts of the complete quantum mechanical networks can be probed experimentally via high-resolution, energy-resolved spectroscopic techniques. The complete rovibronic line list information for a given molecule can only be obtained through sophisticated quantum-chemical computations. Experiments as well as computations yield what we call spectroscopic networks (SN). First-principles SNs of even small, three to five atomic molecules can be huge, qualifying for the big data description. Besides helping to interpret high-resolution spectra, the network-theoretical view offers several ideas for improving the accuracy and robustness of the increasingly important information systems containing line-by-line spectroscopic data. For example, the smallest number of measurements necessary to perform to obtain the complete list of energy levels is given by the minimum-weight spanning tree of the SN and network clustering studies may call attention to weakest links of a spectroscopic database. A present-day application of spectroscopic networks is within the MARVEL (Measured Active Rotational-Vibrational Energy Levels) approach, whereby the transitions information on a measured SN is turned into experimental energy levels via a weighted linear least-squares refinement. MARVEL has been used successfully for 15 molecules and allowed to validate most of the transitions measured and come up with energy levels with well-defined and realistic uncertainties. Accurate knowledge of the energy levels with computed transition intensities allows the realistic prediction of spectra under many different circumstances, e.g., for widely different temperatures. Detailed knowledge of the energy level structure of a molecule coming from a MARVEL analysis is important for a considerable number of modeling efforts in chemistry, physics, and engineering.


PubMed | MTA ELTE Complex Chemical Systems Research Group
Type: Journal Article | Journal: The journal of physical chemistry. A | Year: 2015

An additive, linear, atom-type-based (ATB) scheme is developed allowing no-cost estimation of zero-point vibrational energies (ZPVE) of neutral, closed-shell molecules in their ground electronic states. The atom types employed correspond to those defined within the MM2 molecular mechanics force field approach. The reference training set of 156 molecules cover chained and branched alkanes, alkenes, cycloalkanes and cycloalkenes, alkynes, alcohols, aldehydes, carboxylic acids, amines, amides, ethers, esters, ketones, benzene derivatives, heterocycles, nucleobases, all the natural amino acids, some dipeptides and sugars, as well as further simple molecules and ones containing several structural units, including several vitamins. A weighted linear least-squares fit of atom-type-based ZPVE increments results in recommended values for the following atoms, with the number of atom types defined in parentheses: H(8), D(1), B(1), C(6), N(7), O(3), F(1), Si(1), P(2), S(3), and Cl(1). The average accuracy of the ATB ZPVEs is considerably better than 1 kcal mol(-1), that is, better than chemical accuracy. The proposed ATB scheme could be extended to many more atoms and atom types, following a careful validation procedure; deviation from the MM2 atom types seems to be necessary, especially for third-row elements.

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