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Exact quantum dynamics calculations are performed for the bound rovibrational states of the neon tetramer (Ne4) in its ground electronic state, using pair-wise Lennard-Jones potentials and the ScalIT suite of parallel codes. The vibrational states separate into a low-lying group mostly localized to a single potential well and a higher-energy delocalized group lying above the isomerization threshold—with such a structure serving as a testament to the "intermediate" quantum nature of the Ne4 system. To accurately and efficiently represent both groups of states, the phase-space optimized discrete variable representation (PSO-DVR) approach was used, as implemented in the ScalIT code. The resultant 1D PSO effective potentials also shed significant light on the quantum dynamics of the system. All vibrational states were computed well up into the isomerization band and labeled up to the classical isomerization threshold—defined as the addition of the classical energy of a single bond, ϵ = 24.7 cm−1, to the quantum ground state energy. Rovibrational energy levels for all total angular momentum values in the range J = 1–5 were also computed, treating all Coriolis coupling exactly. [ABSTRACT FROM AUTHOR]

New MiZo line lists are presented for the D2H+ and D |$_3^+$| isotopologues of H |$_3^+$|⁠. These line lists plus the existing H |$_3^+$| MiZATeP and the ST H2D+ line lists are updated using empirical energy levels generated using the marvel procedure for H |$_3^+$|⁠ , H2D+, and D2H+, and effective Hamiltonian energies for D |$_3^+$| for which there is significantly less laboratory data available. These updates allow accurate frequencies for far infrared lines for these species to be predicted. Assignments of the energy levels of H |$_3^+$| and D |$_3^+$| are extended using a combination of high accuracy variational calculations and analysis of transition intensities. All line lists are made av ailable via www.exomol.com. [ABSTRACT FROM AUTHOR]

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 H+5≡[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-nD+n, 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. [ABSTRACT FROM AUTHOR]

The fourth-age quantum chemical code GENIUSH is used for the variational determination of rotational-vibrational energy levels corresponding to reduced- and full-dimensional models of H+ 5 , a molecular ion exhibiting several strongly coupled large-amplitude motions. The computations are supplemented with one- and two-dimensional analytic results which help to understand the peculiar rovibrational energy-level structure computed correctly for the first time. An unusual aspect of the results is that the canonical Eckart-embedding of molecule-fixed axes, a cornerstone of the computational spectroscopy of semirigid molecules, is found to be inadequate. Furthermore, it is shown that while the 1D "active torsion" model provides proper results when compared to the full, 9D treatment, models excluding the torsion have limited physical significance. The structure of the rovibrational energy levels of H+ 5 proves that this is a prototypical astructural molecule: the rotational and vibrational level spacings are of the same order of magnitude and the level structure drastically deviates from that computed via perturbed rigid-rotor and harmonic-oscillator models. [ABSTRACT FROM AUTHOR]

The fourth-age quantum chemical code GENIUSH is used for the variational determination of rotational-vibrational energy levels corresponding to reduced- and full-dimensional models of H+ 5 , a molecular ion exhibiting several strongly coupled large-amplitude motions. The computations are supplemented with one- and two-dimensional analytic results which help to understand the peculiar rovibrational energy-level structure computed correctly for the first time. An unusual aspect of the results is that the canonical Eckart-embedding of molecule-fixed axes, a cornerstone of the computational spectroscopy of semirigid molecules, is found to be inadequate. Furthermore, it is shown that while the 1D "active torsion" model provides proper results when compared to the full, 9D treatment, models excluding the torsion have limited physical significance. The structure of the rovibrational energy levels of H+ 5 proves that this is a prototypical astructural molecule: the rotational and vibrational level spacings are of the same order of magnitude and the level structure drastically deviates from that computed via perturbed rigid-rotor and harmonic-oscillator models. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The variational nuclear-motion codes ElVibRot and GENIUSH have been used to compute rotational–vibrational states of the F−(H2O) anion and its deuterated isotopologue, F−(D2O), employing a full-dimensional, semiglobal potential energy surface (PES) called SLBCL, developed as part of this study for the ground electronic state of the complex. The PES is determined from all-electron, explicitly correlated coupled-cluster singles, doubles, and connected triples [CCSD(T)-F12a] computations with an atom-centered, fixed-exponent Gaussian basis set of cc-pCVTZ-F12 quality. The SLBCL PES accurately reproduces the two equivalent minima of the complex, the corresponding transition barrier of C2v point-group symmetry, as well as the proton transfer and the dissociation asymptotes towards the products HF + OH− and F− + H2O, respectively. The code ElVibRot has been updated so that it can use curvilinear internal coordinates corresponding to a reaction path. The variationally computed vibrational energy levels are compared to relevant experimental and previously determined first-principles results. The vibrational states reveal the presence of pronounced anharmonic effects and considerable intermode couplings resulting in strong resonances, involving in particular the HOH bend and the ionic OH stretch motions. Tunneling results in particularly significant splittings for F−(H2O); as expected, the splittings are orders of magnitude smaller for the F−(D2O) molecule. The rovibrational energy levels reveal that, despite the large-amplitude vibrational motions, the rotations of F−(H2O) basically follow rigid-rotor characteristics. [ABSTRACT FROM AUTHOR]

The concept of quasistructural molecules is introduced. For quasistructural molecules (a) the notion of a static equilibrium structure, corresponding to a minimum on the potential energy surface of the molecule, loses its strict meaning, (b) internal nuclear motions (rotations and vibrations) become dominant, resulting in an effective molecular structure often even qualitatively different from the equilibrium one, (c) separation of the internal nuclear motions breaks down, rotational and vibrational degrees of freedom cannot be separated from each other when interpreting even the lowest rovibrational eigenstates of the molecule, often resulting in effective rotational constants drastically different from the equilibrium ones even for the ground vibrational eigenstate, (d) classification of the rovibrational states requires the use of permutation‐inversion symmetry and molecular‐symmetry groups, and (e) some of the rovibrational eigenenergies assigned to a vibrational parent state exhibit unconventional (in the most striking cases "negative") rotational contributions. Molecules showing quasistructural behavior include neutral species, such as dimethyl acetylene, charged species, such as H5+ and CH5+, van der Waals complexes, such as CH4·H2O, and molecular complexes held together by halogen bonds, like CF3Cl·CH3F. This article is categorized under: Structure and Mechanism > Molecular StructuresTheoretical and Physical Chemistry > SpectroscopySoftware > Quantum Chemistry [ABSTRACT FROM AUTHOR]

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 D 0 = 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 variational nuclear-motion codes ElVibRot and GENIUSH have been used to compute rotational-vibrational states of the F(-)(H2O) anion and its deuterated isotopologue, F(-)(D2O), employing a full-dimensional, semiglobal potential energy surface (PES) called SLBCL, developed as part of this study for the ground electronic state of the complex. The PES is determined from all-electron, explicitly correlated coupled-cluster singles, doubles, and connected triples [CCSD(T)-F12a] computations with an atom-centered, fixed-exponent Gaussian basis set of cc-pCVTZ-F12 quality. The SLBCL PES accurately reproduces the two equivalent minima of the complex, the corresponding transition barrier of C2v point-group symmetry, as well as the proton transfer and the dissociation asymptotes towards the products HF + OH(-) and F(-) + H2O, respectively. The code ElVibRot has been updated so that it can use curvilinear internal coordinates corresponding to a reaction path. The variationally computed vibrational energy levels are compared to relevant experimental and previously determined first-principles results. The vibrational states reveal the presence of pronounced anharmonic effects and considerable intermode couplings resulting in strong resonances, involving in particular the HOH bend and the ionic OH stretch motions. Tunneling results in particularly significant splittings for F(-)(H2O); as expected, the splittings are orders of magnitude smaller for the F(-)(D2O) molecule. The rovibrational energy levels reveal that, despite the large-amplitude vibrational motions, the rotations of F(-)(H2O) basically follow rigid-rotor characteristics.