Rg Atoms Research Articles

Investigation of the Electronic Excited States of Small Gold Clusters in Rare Gas Matrices: Spin-Orbit Time-Dependent Density Functional Theory Calculation.

The effects of the weak interactions of rare gas atoms on the UV-visible absorption spectra of gold dimer and tetramer clusters are investigated. The time-dependent density functional theory based on the two-component relativistic zeroth-order regular approximation that considered spin-orbit coupling is performed to estimate the absorption spectra of Au2,4-Rgn (Rg = Ne-Xe, and n = 1-6) complexes. Using spin-orbit, including the appropriate functional, shows a close correlation between experiment and our calculations. It is also demonstrated that the weak interactions between rare gas atoms and gold clusters affect the UV-vis spectra of Au2,4 clusters by shifting the electronic transition toward the blue. Moreover, we find that the order of change in peak position, Δν̃, is proportional to the strength of interactions: Δν̃Au2,4-Xe > Δν̃Au2,4-Kr > Δν̃Au2,4-Ar > Δν̃Au2,4-Ne. In addition, comparing the UV-visible spectra of Au2,4-Rgn complexes with those of isolated Au2 and Au4 clusters shows that for Au2,4-Rg2,4,6 complexes in which Rg atoms interacted symmetrically with gold clusters no additional peaks are observed compared to isolated clusters; however, for Au2,4-Rg1,3,5 complexes, extra peaks appear because of the decrease in symmetry.

HM⁺-RG complexes (M = group 2 metal; RG = rare gas): Physical vs. chemical interactions.

Previous work on the HM(+)-He complexes (M = Be-Ra) has been extended to the cases of the heavier rare gas atoms, HM(+)-RG (RG = Ne-Rn). Optimized geometries and harmonic vibrational frequencies have been calculated using MP2 theory and quadruple-ζ quality basis sets. Dissociation energies for the loss of the rare gas atom have been calculated at these optimized geometries using coupled cluster with single and double excitations and perturbative triples, CCSD(T)theory, extrapolating interaction energies to the basis set limit. Comparisons are made between the present data and the previously obtained helium results, as well as to those of the bare HM(+) molecules; furthermore, comparisons are made to the related M(+)-RG and M(2+)-RG complexes. Partial atomic charge analyses have also been undertaken, and these used to test a simple charge-induced dipole model. Molecular orbital diagrams are presented together with contour plots of the natural orbitals from the quadratic configuration with single and double excitations (QCISD) density. The conclusion is that the majority of these complexes are physically bound, with very little sharing of electron density; however, for M = Be, and to a lesser extent M = Mg, some evidence for chemical effects is seen in HM(+)-RG complexes involving RG atoms with the higher atomic numbers.

Nature of Brønsted acid–noble atom contacts: A reevaluation of hydrogen bonding criteria

Xenon atoms interact weakly and reversibly with different molecular systems and human body. In this report, we consider their participation in hydrogen bonding in relation to analogous interactions of Ne, Ar, and Kr. Acid–noble atom dimers, AH···Rg, are examined by the quantum theory of atoms in molecules and the results are discussed using several independent parameters. Different factors of this complexation are recognized: (i) the AH acidity and the Rg basicity, (ii) the AH structure, (iii) the electronegativities of atoms A and Rg, and (iv) the charge transfer from Rg to the complex critical point and to the acidic H atom. AH···Ne contacts are qualitatively different from the remaining complexes. Koch and Popelier's criteria of hydrogen bonding, developed for classic complexes, are usually fulfilled for these very weak systems with one main exception: the charge on the acidic H increases upon the complexation to bigger Rg atoms. © 2014 Wiley Periodicals, Inc.

Theoretical Prediction of Rare Gas Containing Hydride Cations: HRgBF+(Rg = He, Ar, Kr, and Xe)

The existence of rare-gas-containing hydride ions of boron (HRgBF(+)) has been predicted by using ab initio quantum chemical methods. The HRgBF(+) ions are obtained by inserting a rare gas (Rg) atom in between the H and B atoms of a HBF(+) ion, and the geometries are optimized for minima as well as transition states using second-order Møller-Plesset perturbation theory (MP2), density functional theory (DFT), and coupled-cluster theory (CCSD(T)) based techniques. The predicted HRgBF(+) ions are found to be metastable, and they exhibit a linear structure at the minima and a nonlinear planar structure at the transition state, corresponding to C∞v and Cs symmetries, respectively. All of the predicted HRgBF(+) ions show negative binding energies with respect to the two-body dissociation channel, leading to global minima (HBF(+) + Rg) on the singlet potential energy surface. In contrast, the dissociation energies corresponding to another two-body dissociation channel leading to HRg(+) + BF and two three-body dissociation channels corresponding to the dissociation into H + Rg + BF(+) and H(+) + Rg + BF show very high positive energies. Apart from positive dissociation energies, the predicted ions show finite barrier heights corresponding to the transition states involving a H-Rg-B bending mode, leading to the global minima products (HBF(+) + Rg). The finite barrier heights in turn would prevent the metastable HRgBF(+) species from transforming to global minima products. Structure, harmonic vibrational frequencies, stability, and Mulliken and natural bonding orbital (NBO) charge distribution values for all of the species are reported using the MP2 and DFT methods. Furthermore, the intrinsic reaction coordinate analysis confirms that the metastable minimum-energy structure and the global minimum products are connected through the corresponding transition state for each of the species on the respective singlet potential energy surface. Atoms-in-molecules (AIM) analysis indicates that the HRgBF(+) ions are best described as HRg(+)BF and are analogous to the isoelectronic HRgCO(+) and HRgN2(+) ions. The energetic along with charge redistribution and spectroscopic data strongly support the possible existence of HRgBF(+) ions. Hence, it might be possible to generate HRgBF(+) ions in the DC discharge plasma of a BF3/H2/Rg mixture at low temperature, and the predicted ions may be characterized using the magnetic field modulated infrared laser spectroscopic technique, which has been used earlier to characterize HBF(+) ions.

Theoretical Study of M+–RG2(M+= Li, Na, Be, Mg; RG = He–Rn)

Ab initio calculations were employed to determine the geometry (MP2 level), and dissociation energies [MP2 and RCCSD(T) levels], of the M(IIa)(+)-RG2 species, where M(IIa) is a group 2 metal, Be or Mg, and RG is a rare gas (He-Rn). We compare the results with similar calculations on M(Ia)(+)-RG2, where M(Ia) is a group 1 metal, Li or Na. It is found that the complexes involving the group 1 metals are linear (or quasilinear), whereas those involving the group 2 metals are bent. We discuss these results in terms of hybridization and the various interactions in these species. Trends in binding energies, D(e), bond lengths, and bond angles are discussed. We compare the energy required for the removal of a single RG atom from M(+)-RG2 (D(e2)) with that of the dissociation energy of M(+)-RG (D(e1)); some complexes have D(e2) > D(e1), some have D(e2) < D(e1), and some have values that are about the same. We also present relaxed angular cuts through a selection of potential energy surfaces. The trends observed in the geometries and binding energies of these complexes are discussed. Mulliken, natural population, and atoms-in-molecules (AIM) population analyses are performed, and it is concluded that the AIM method is the most reliable, giving results that are in line with molecular orbital diagrams and contour plots; unphysical amounts of charge transfer are suggested by the Mulliken and natural population approaches.

Global Potentials for the Interaction between Rare Gases and Graphene-Based Surfaces: An Atom–Bond Pairwise Additive Representation

Global potentials for the physisorption of rare-gas atoms on graphene and graphite, amenable for a variety of dynamics simulations, are reported. An atom–bond pairwise additive form of the potential is used, where the interaction pairs, represented by proper analytical functions, are constituted by the Rg atom (Rg = He, Ne, Ar, Kr) and the C–C bonds of the graphene sheet(s). The parameters of the atom–bond pair potential, derived from the polarizability of the interacting partners, are fine-tuned, exploiting calculations of the prototypical Rg–coronene system using high-level electronic structure methods and large basis sets. The atom–graphene/graphite potential is further expanded in a Fourier series, and it is found that for an accurate representation of the interaction only a small number of corrugation terms need to be added to the laterally averaged potential. Furthermore, this corrugation part of the potential is both identical for Rg–graphene and Rg–graphite; in other words, inner layers of graphit...

AB INITIO AND DFT STUDY OF NON-COVALENT INTERACTIONS BETWEEN RARE GAS ATOMS AND AROMATIC RINGS

In this paper, the weak interaction between aromatic rings (ARs) and rare gas (Rg) atoms has been studied using ab initio calculation and density functional theory (DFT). The augmented Dunning basis sets were used, and the convergence test was performed up to aug-cc-pV5Z. Among the computationally feasible methods, ωB97XD performed the best for these non-covalent systems. NBO analysis was performed to investigate the nature of the Rg/AR interactions. In this type of weak interaction, the induced and instantaneous dipole and charge transfer character both contribute to the interaction energies and equilibrium distances.

New Medium-size Basis Sets for Rare-gas Atoms

New medium-size basis sets are constructed for rare-gas (Rg) atoms and tested on their dimers Rg2. The main part of the these bases contains the standard aug-cc-pVTZ basis set modified and extended by the g- and h-polarization functions. Their optimization allows accurate calculations of the dispersion interaction without the involvement of the bond functions. A new convenient analytical potential function is invented to fit accurately the interaction energy. The potentials derived for Rg dimers predict the vibrational transition energies and rotational constants to accuracy of 1%.

Interactions in the B+–RG Complexes and Comparison with Be+–RG (RG = He–Rn): Evidence for Chemical Bonding

Potential energy curves for the interaction of B(+) ((1)S) with RG ((1)S), RG = He-Rn, have been calculated at the CCSD(T) level of theory employing quadruple-ζ and quintuple-ζ quality basis sets. The interaction energies from these curves were subsequently point-by-point extrapolated to the basis set limit. Rovibrational energy levels have been calculated for each extrapolated curve, from which spectroscopic parameters are determined. These are compared to previously determined experimental and theoretical values. The potentials have also been employed to calculate the transport coefficients for B(+) traveling through a bath of RG atoms. We also investigate the interactions between B(+) and the rare gases via contour plots, natural population analysis (NPA), and molecular orbital diagrams. In addition, we consider the atoms-in-molecules (AIM) parameters. The interactions here are compared and contrasted with those for Li(+)-He and Be(+)-RG; it is concluded that there is significant and increasing dative covalent bonding for the Be(+)-RG and B(+)-RG complexes for RG = Ar-Rn, while the other species are predominantly physically bound.

Cooperativity between S···π and Rg···π in the OCS···C6H6···Rg (Rg = He, Ne, Ar, and Kr) van der Waals Complexes

The complexes OCS···C(6)H(6), C(6)H(6)···Rg, and OCS···C(6)H(6)···Rg (Rg = He, Ne, Ar, and Kr) have been studied by means of MP2 calculations and QTAIM analyses. The optimized geometries of the title complexes have C(6v) symmetry. The intermolecular interactions in the OCS···C(6)H(6)···Rg complexes are comparatively stronger than that in the OCS···C(6)H(6) complex, which prove that the He, Ne, Ar, and Kr atoms have the ability to form weak bonds with the benzene molecule. In QTAIM studies, the π-electron density of benzene was separated from the total electron density. The molecular graphs and topological parameters of the OCS···πC(6)H(6), πC(6)H(6)···Rg, and OCS···πC(6)H(6)···Rg complexes indicate that the interactions are mainly attributed to the electron density provided by the π-bonding electrons of benzene and the top regions of the S and Rg atoms. Charge transfer is observed from the benzene molecule to SCO/Rg in the formation of the OCS···C(6)H(6), C(6)H(6)···Rg, and OCS···C(6)H(6)···Rg complexes. Molecular electrostatic potential (MEP) analyses suggest that the electrostatic energy plays a pivotal role in these intermolecular interactions.

Interactions of ThO(X) with He, Ne and Ar from the ab initio coupled cluster and symmetry adapted perturbation theory calculations

Two-dimensional interaction potential energy surfaces for the ground-state ThO complexes with RG atoms from He to Ar are calculated ab initio at the coupled cluster CCSD(T) level of theory. The global minimum for all complexes is related to a bent geometry, with the RG atom closer to the oxygen end. Parallel symmetry adapted perturbation theory (SAPT) calculations for the ThO–He complex showed that this configuration is favored by the exchange interaction that slightly prevails over the dispersion and induction contributions which prefer the collinear arrangement. Variational calculations of rovibrational energy levels provided the dissociation energies of 9, 15 and 184cm−1, for the 3He, Ne and Ar complexes, respectively. The He and Ne complexes in the ground state resemble linear molecules as their zero-point energies exceed the barrier at the linear RG–OTh arrangement. Vibrationally-averaged structure of the Ar–ThO complex better reflects the bent geometry of the equilibrium point.

RgBF2+ complexes (Rg = Ar, Kr, and Xe): The cations with large stabilities

Rare gas containing cations with general formula [Rg, B, 2F](+) have been investigated theoretically by second-order Mo̸ller-Plesset perturbation, coupled cluster, and complete active space self-consistent field levels of theory with correlation-consistent basis sets. Totally two types of minima, i.e., boron centered C(2) (v) symmetried RgBF(2) (+) (Rg = Ar, Kr, and Xe) which can be viewed as loss of F(-) from FRgBF(2) and linear FRgBF(+) (Rg = Kr and Xe) are obtained at the CCSD(T)∕aug-cc-pVTZ∕SDD and CASSCF(10,8)∕aug-cc-pVTZ∕SDD levels, respectively. It is shown that the RgBF(2) (+) are global minima followed by FRgBF(+) at 170.9 and 142.2 kcal∕mol on the singlet potential-energy surfaces of [Rg, B, 2F](+) (Rg = Kr and Xe) at the CASPT2(10,8) ∕aug-cc-pVTZ∕SDD∕∕CASSCF(10,8)∕aug-cc-pVTZ∕SDD, respectively. The interconversion barrier heights between RgBF(2) (+) and FRgBF(+) (Rg = Kr and Xe) are at least 39 kcal∕mol. In addition, no dissociation transition state associated with RgBF(2) (+) and FRgBF(+) can be found. This suggests that RgBF(2) (+) (Rg = Ar, Kr, and Xe) can exist as both thermodynamically and kinetically stable species, while linear FRgBF(+) (Rg = Kr and Xe) can exist as metastable species compared with the lowest dissociation limit energies just like isoelectronic linear FRgBO and FRgBN(-). From natural bond orbital and atoms-in-molecules calculations, it is found that the positive charge is mainly located on Rg and boron atoms for both types of minima, the Rg-B bonds of ArBF(2) (+), KrBF(2) (+), and XeBF(2) (+) are mostly electrostatic, thus can be viewed as ion-induced dipole interaction; while that of linear FKrBF(+) and FXeBF(+) are covalent in nature. The previous experimental observation of ArBF(2) (+) by Pepi et al. [J. Phys. Chem. B. 110, 4492 (2006)] should correspond to C(2) (v) minimum. The presently predicted spectroscopies of KrBF(2) (+), XeBF(2) (+), FKrBF(+), and FXeBF(+) should be helpful for their experimental identification in the future.

Theoretical Study of M+−RG Complexes (M = Ga, In; RG = He−Rn)

We present potential energy curves calculated at the CCSD(T) level of theory for Ga(+)-RG and In(+)-RG complexes (RG = He-Rn). Spectroscopic parameters have been derived from these potentials and compared to previously calculated parameters for the Al(+)-RG and Tl(+)-RG complexes. Additionally, for some cases, we compare these parameters with those obtained from electronic spectroscopic studies on excited states of the neutral species, arising from atomic-based d ← p excitations. The Ga(+)-RG and In(+)-RG potentials have also been used to calculate the transport coefficients for M(+) traveling through a bath of RG atoms.

QED corrections for the valence electron in heavy and super-heavy atoms

The radiative QED corrections for the valence electron of the neutral Rg (Z = 111) atom are estimated within the framework of the post-Dirac–Fock method. In this method the Koopmans’ approximation is proposed for the electron propagator in the QED diagrams. Such calculation is done for the first time for this super-heavy atom. These results contribute to the discussion concerning the accuracy of the QED corrections in the super-heavy elements. They also provide the accuracy limit of the modern relativistic theoretical calculations for the super-heavy elements.

Theoretical Study of M+−RG and M2+−RG Complexes and Transport of M+ through RG (M = Be and Mg, RG = He−Rn)

We present high level ab initio potential energy curves for the M(n+)-RG complexes, where n = 1, 2, RG = rare gas, and M = Be and Mg. Spectroscopic constants have been derived from these potentials, and they generally show very good agreement with the available experimental data. The potentials have also been employed in calculating transport coefficients for M(+) moving through a bath of RG atoms, and the isotopic scaling relationship is examined for Mg(+) in Ne. Trends in binding energies, D(e), and bond lengths, R(e), are discussed and compared to similar ab initio results involving the corresponding complexes of the heavier alkaline earth metal ions. We identify some very unusual behavior, particularly for Be(+)-Ne, and offer possible explanations.

Theoretical study of the X Σ2+ states of the neutral CM–RG complexes (CM=coinage metal, Cu, Ag, and Au and RG=rare gas, He–Rn)

We present high level ab initio potential energy curves for the X Σ2+ electronic states of the CM–RG complexes; where CM is a coinage metal, CM=Cu, Ag and Au and RG is a rare gas, RG=He–Rn. These potentials are calculated over a range of internuclear separations, R, and the energy at each point is corrected for basis set superposition error and extrapolated to the basis set limit. Spectroscopic constants are determined from the potentials so obtained and are compared to available experimental data. The impact of core-valence correlation to the overall interactions within the complexes involving the lighter RG atoms is also considered. We find that there is a surprising continuous decrease in Re in these species from CM-He to CM-Rn and show that this is likely due to a combination of sp hybridization and small amounts of charge transfer.

Comparative study of rare gas-H2 triatomic complexes

This paper presents a comparative analysis of complexes made of one rare gas (Rg) atom and molecular hydrogen, for five different Rg atoms. In particular, the vibrational band origins have been calculated, as well as the structural properties of the associated wavefunctions. The study is extended to ultra-cold Rg–H2 collisions, object of a recent experiment aimed at producing ultra-cold H2 [1]. The molecular systems are studied variationally using a simple, yet effective, isotropic trial wavefunction. A large number of potential energy surfaces available from the literature is considered. A comparative analysis shows that differences of up to two orders of magnitude exist for the zero-energy elastic cross sections of the five complexes. Corrections to the isotropic model have also been considered, showing no significant effect.

Interaction of NO(A Σ2+) with rare gas atoms: Potential energy surfaces and spectroscopy

We present the results of an ab initio study of the interaction of electronically excited NO(A (2)Sigma(+)) with rare gas (Rg) atoms. The bound states of each NO(A)-Rg species are determined from potential energy surfaces calculated at the RCCSD(T) level of theory. Making use of the NO(X (2)Pi)-Rg vibrational wavefunctions, we then simulate electronic spectra. For NO-Kr and NO-Xe we obtain good qualitative agreement with the previously published experimental spectra. For NO-Ar, the shallowness of the surface gives rise to agreement that is less satisfactory, but a global scaling provides better qualitative agreement. The assignment of the spectra is far from straightforward and is only possible with guidance from the calculated energies and wavefunctions of the energy levels of the complex. Previous assignments are discussed in the light of this conclusion.

Ab initio intermolecular potential energy surfaces of the water-rare gas atom complexes

Highly accurate analytical intermolecular potential energy surfaces (PESs) of the complexes composed of the water molecule and the rare gas (Rg) atom are presented for Rg=He, Ne, Ar, and Kr. These PESs were scanned using the supermolecule coupled cluster singles and doubles including connected triples method [CCSD(T)]. Efficient basis sets including the bond functions (3s3p2d1f1g) enabled the calculation of more than 430 single-point interaction energies for each complex. These energies were utilized to construct the analytical many-body representations of the PESs. They were refined using the interaction energies evaluated at the complete basis set limit in the PES stationary points. In addition, the corrections from the core correlation were calculated for the complexes including He, Ne, and Ar. The many-body PES of XeH(2)O was built using the ab initio energy values reported by Wen and Jager [J. Phys. Chem. A 110, 7560 (2006)]. The clear regularities of the equilibrium structure and the potential barriers were found in the RgH(2)O series. A comparison of the ab initio and experimental PESs of ArH(2)O [R. C. Cohen and R. J. Saykally, J. Chem. Phys. 98, 6007 (1993)] reveals their close similarity, except for the potential barriers corresponding to the planar saddle points. Their energetic order is different in both PESs. This suggests that an alternative PES with the reversed barriers, consistent with the ab initio ones, could be derived from the experimental data.

Theoretical prediction of HRgCO+ ion (Rg=He, Ne, Ar, Kr, and Xe)

Ab initio quantum chemical methods have been employed to investigate the structure, stability, charge redistribution, and harmonic vibrational frequencies of rare gas (Rg=He, Ne, Ar, Kr, and Xe) containing HRgCO(+) ion. The Rg atoms are inserted in between the H and C atoms of HCO(+) ion and the geometries are optimized for minima as well as transition state using second order Moller-Plesset perturbation theory, density functional theory, and coupled-cluster theory [CCSD(T)] methods. The HRgCO(+) ions are found to be metastable and exhibit a linear structure at the minima position and show a nonlinear structure at the transition state. The predicted ion is unstable with respect to the two-body dissociation channel leading to the global minima (HCO(+)+Rg) on the singlet potential surface. The binding energies corresponding to this channel are -406.4, -669.3, -192.3, -115.4, and -52.2 kJ mol(-1) for HHeCO(+), HNeCO(+), HArCO(+), HKrCO(+), and HXeCO(+) ions, respectively, at CCSD(T) method. However, with respect to other two-body dissociation channel, HRg(+)+CO, the ions are found to be stable and have positive energies except for HNeCO(+) at the same level of theory. The computed binding energies for this channel are 15.0, 28.8, 29.5, and 29.1 kJ mol(-1) for HHeCO(+), HArCO(+), HKrCO(+), and HXeCO(+) ions, respectively. Very high positive three-body dissociation energies are found for H+Rg+CO(+) and H(+)+Rg+CO dissociation channels. It indicates the existence of a very strong bonding between Rg and H atoms in HRgCO(+) ions. The predicted ions dissociate into global minima, HCO(+)+Rg, via a transition state involving H-Rg-C bending mode. The barrier heights for the transition states are 22.7, 10.1, 13.1, and 15.0 kJ mol(-1) for He, Ar, Kr, and Xe containing ions, respectively. The computed two-body dissociation energies are comparable to that of the experimentally observed mixed cations such as ArHKr(+), ArHXe(+), and KrHXe(+) in an electron bombardment matrix isolation technique. Thus HRgCO(+) cations may also be possible to prepare and characterize similar to the mixed cations (RgHRg('))(+) in low temperature matrix isolation technique.