HXeOBr in a xenon matrix

Noble gas dative bonding with coinage metal carbene complexes: A theoretical study

The structure and stability of noble gas (Ng) bound [NHCM]+ complexes (M = Cu, Ag, and Au) were investigated using Quantum chemical calculations. Dissociation energies, enthalpy, and free energy changes were computed to comprehend the stability of these Ng-bonded complexes. The nature of interactions associated to the bonding between metal and noble gas atoms was studied through the computation of electron density-based descriptors. Detailed electronic structure study revealed electron donation from the noble gas atoms towards the metal center, resulting in the formation of dative bonds.

Theoretical prediction of donor-acceptor type novel complexes with strong noble gas-boron covalent bond

The experimental identification of NgBeO molecules, followed by the recent theoretical exploration of super-strong NgBO+ (Ng = He-Rn) ions motivated us to investigate the stability of iso-electronic NgBNH+ (Ng = He-Rn) ions using various ab initio-based quantum chemical methods. The hydrogen-like chemical behavior of gold in small clusters and molecules also inspired us to study the nature of the bonding interactions in NgBNAu+ ions compared to that in NgBNH+ ions. The calculated Ng-B bond lengths in the predicted ions have been found to be much lower than the corresponding covalent limits, indicating a covalent Ng-B interaction in both the NgBNH+ and NgBNAu+ ions. In addition, the Ng-B bond dissociation energies are found to be in the range of 136.7-422.8 kJ mol-1 for NgBNH+ and 77.4-319.1 kJ mol-1 for NgBNAu+, implying the stable nature of the predicted ions. Interestingly, the Ng-B bond length (except for Ne) is the lowest reported to date together with the highest He-B and Ne-B binding energies considering all the neutral and cationic complexes containing Ng-B bonding motifs. Moreover, the natural bonding orbital (NBO) and electron density-based atoms-in-molecule (AIM) analysis reveal the covalent nature of the Ng-B bond in the predicted ions. Furthermore, the energy decomposition analysis together with the natural bond orbital in the chemical valence (EDA-NOCV) studies indicate that the orbital interaction energy is the main contributor to the total attraction energy in the Ng-B bonds. All the calculated results indicate the hydrogen-like chemical behavior of gold in the predicted NgBNM+ ions, showing further evidence of the concept of "gold-hydrogen analogy". Also, for comparison, the corresponding Cu and Ag analogs are investigated. All the computed results together with the experimental identification of the NgMX (Ng = Ar-Xe; M = Cu, Ag, Au; X = F, Cl), ArOH+, and NgBeO (Ng = Ar-Xe) systems clearly indicate that it may be possible to prepare and characterize the predicted NgBNM+ ions experimentally using suitable technique(s).

Prediction of donor-acceptor-type novel noble gas complexes in the triplet electronic state

Closed-shell noble gas (Ng) compounds in the singlet electronic state have been extensively studied in the past two decades after the revolutionary discovery of ¹HArF molecule. Motivated by the experimental identification of very strong donor-acceptor-type singlet-state Ng complex ¹ArOH⁺, in the present article, for the first time, we report new donor-acceptor-type noble gas complexes in the triplet electronic state (³NgBeN⁺ (Ng = He-Rn)), where most of the Ng-Be bond lengths are smaller than the corresponding covalent limits. The newly proposed complexes are predicted to be stable by various computational tools, including coupled-cluster and multireference-based methods, with strong Ng-Be bonding (40.4-196.2 kJ mol^-1). We have also investigated ³NgBeP⁺ (Ng = He-Rn) complexes for the purpose of comparison. Various computational results, including the structural parameters, bonding energies, vibrational frequencies, and atoms-in-molecule properties suggest that it may be possible to prepare and characterize these triplet state complexes through suitable experimental technique(s).

Superstrong Chemical Bonding of Noble Gases with Oxidoboron (BO+) and Sulfidoboron (BS+)

Inspired by the overwhelming exploration of noble gas-boron (Ng-B) bond containing chemical compounds, the stability of the Ng bound BY⁺ and AlY⁺ (Y = O and S) has been investigated by using various ab initio based quantum chemical methods. Ng atoms are found to form exceptionally strong bonds with BO⁺ species in the predicted NgBO⁺ (Ng = He-Rn) complexes with remarkably high Ng-B dissociation energies ranging from 138.0 to 462.2 kJ mol^-1 for the He-Rn series. It is the highest ever Ng-B binding energy in conjunction with the smallest Ng-B bond length for any of the cationic species involving a Ng-B bond as reported until today. More importantly, the calculated Ng-B bond lengths have been found to be much lower than the respective covalent limits in both NgBO⁺ and NgBS⁺ ions. The electronegativity difference between O and S atoms has been reflected nicely in the Ng-B and Ng-Al binding energies, which are found to be 91.9-346.5, 9.6-169.2, and 6.8-142.1 kJ mol^-1 in NgBS⁺, NgAlO⁺, and NgAlS⁺, respectively. The strong covalent bonding between Ng and B/Al atoms in the predicted chemical systems has also been supported by the natural bonding orbital (NBO) and electron density based atoms-in-molecule (AIM) analysis. In addition, the energy decomposition analysis (EDA) in combination with the natural bond orbital for chemical valence (NOCV) indicates that the orbital interaction term is the prime contributor to the total attraction energy in the Ng-B and Ng-Al bonds. Furthermore, Ng-B and Ng-Al bonding can be assessed using the donor-acceptor model where the σ-electron donation that takes place from Ng (HOMO) → XY⁺ (LUMO) (X = B and Al; Y = O and S) is the major contributor to the orbital interaction energy. All the computational results along with the very recent experimental observation of ArOH⁺ and NgMX (Ng = Ar-Xe; M = Cu, Ag, Au; X = F, Cl) clearly indicate that it might be possible to synthesize and characterize these superstrong complexes, NgXY⁺ (Ng = He-Rn; X = B and Al; Y = O and S), under suitable experimental technique(s).

Stability-Order Reversal in FSiY and FYSi (Y = N and P) Molecules after the Insertion of a Noble Gas Atom

Recent theoretical prediction and experimental identification of fluorinated noble gas cyanides and isocyanides motivate us to explore a unique novel series of neutral noble gas-inserted heavier cyanofluoride isomers, FNgYSi and FNgSiY (Ng = Kr, Xe, and Rn; Y = N and P), theoretically using quantum chemical calculations. The concerned minima and saddle point geometries have been optimized using DFT, MP2, and CCSD(T) methods. The precursor molecule FSiY is more stable than its isomer FYSi, and the stability order is found to be reversed after the insertion of a noble gas (Ng) atom into them which is in contrast to the previously reported FCN/FNC systems where the stability order in the precursors remains intact after the insertion of a Ng atom into them. The predicted FNgYSi molecules are metastable in nature as they are kinetically stable but thermodynamically unstable with respect to the global minima products (FYSi and Ng). All the calculations for the corresponding FNgSiY molecules clearly indicate that the less stable FNgSiY behaves similarly to the FNgYSi in all respects. The energetics, force constant, and spectroscopic data strongly reinforce the possibility of occurrence of these predicted FNgYSi and FNgSiY molecules which might be experimentally realized under suitable cryogenic condition(s).

Existence of Noble Gas Inserted Phosphorus Fluorides: FNgPF2 and FNgPF4 with Ng-P Covalent Bond (Ng = Ar, Kr, Xe and Rn)

Very limited literature on noble gas (Ng)-phosphorous chemical bonding and our recent theoretical prediction of FNgP molecule motivates us to explore a unique novel class of neutral noble gas inserted...

XNgNSi (X = HCC, F; Ng = Kr, Xe, Rn): A New Class of Metastable Insertion Compounds Containing Ng-C/F and Ng-N Bonds and Possible Isomerization therein

Recently, astronomically important silaisocyanoacetylene (HCCNSi) possessing a large dipole moment has been detected for the first time with the help of crossed molecular beam experiments. Quantum chemical computations at higher levels of theory have also been performed to characterize the transient species. In this study, we have analyzed the equilibrium geometry, stability, reactivity, and energetics as well as the nature of bonding in the noble gas (Ng) inserted HCCNSi compound. We have also considered its F analogue to understand the influence of the most electronegative atom in the compound. Metastable behavior of the XNgNSi compounds (X = HCC, F; Ng = Kr-Rn) is examined by calculating thermochemical parameters like free energy change (ΔG) and zero-point-energy-corrected dissociation energy (D₀) at 298 K for all possible two-body (2B) and three-body (3B) (both neutral as well as ionic) dissociation channels using coupled-cluster theory [CCSD(T)] in addition to density functional theory (DFT) as well as second order Møller-Plesset perturbation theory (MP2). The set of predicted compounds is found to be endergonic in nature, having high positive free energy change suggesting the thermochemical stability of the compounds except for the 2B Ng-release paths. Though thermodynamically feasible, they are kinetically protected with very high activation free energy barriers. Interestingly, the release of Ng from the parent moiety XNgNSi produces the XSiN isomer, by 180° flipping of the NSi moiety. This can also be seen in the dynamical simulation carried out with the help of atom-centered density matrix propagation (ADMP) technique at 2000K for 1 ps. The bonding in Ng-C, Ng-F, and Ng-N bonds of the studied compounds is analyzed and described with the aid of natural bond orbital (NBO), topological parameters computed using atoms-in-molecules theory (AIM), energy decomposition analysis (EDA), and adaptive natural density partitioning (AdNDP) methods. The natural charge distribution on the constituent atoms suggests that the compounds can be partitioned into both ways of representations, viz., neutral radical as well as ionic fragments. Lastly, the reactivity of the compounds is scrutinized using certain reactivity descriptors calculated within the domain of conceptual density functional theory (CDFT).

Anomaly in the stability of the hydroxides of icosagens (B and Al) and their noble gas (Xe and Rn) derivatives: a comparative study

Motivated by the discovery of neutral noble gas hydrides, herein, we have explored the possibility of the existence of a novel class of neutral noble gas compounds, HNgBO, HNgOB, HNgAlO and HNgOAl (Ng = Xe and Rn), through the insertion of a Ng atom into the hydroxides of icosagens and their isomers, namely, HBO, HOB, HAlO and HOAl. Second-order Møller-Plesset perturbation theory (MP2), density functional theory (DFT), and coupled-cluster theory (CCSD(T))-based methods have been employed to investigate the structures, stabilities, energetics, harmonic vibrational frequencies, and charge distribution of the predicted molecules. The HXeBO, HXeOAl, HRnBO, HRnAlO and HRnOAl molecules are found to be thermodynamically stable with respect to all plausible 2-body and 3-body dissociation channels except the 2-body dissociation pathway, leading to the formation of global minimum products (Ng + HBO), (Ng + HOAl) and (Ng + HAlO). However, the very large activation energy barrier heights provide enough kinetic stability to the predicted metastable molecules, which in turn can prevent them from dissociating into the global minimum products. Between the HNgBO-HNgOB isomers, HNgBO is found to be more stable, where both HNgBO and the precursor molecule HBO are linear. On the other hand, HNgOAl is more stable between the HNgAlO-HNgOAl isomers, where the precursor molecule HOAl is bent and HNgOAl is linear in contradiction and in agreement with Walsh's rule, respectively. Moreover, in contrast to the more stable HNgBO case, where the Ng atom is bonded with the icosagen atom, in the more stable HNgOAl, the Ng atom is connected to the chalcogen atom. All the detailed aforementioned analyses concerning the predicted molecules clearly indicate that a strong covalent bond exists between the H and Ng atoms, while an ionic interaction is found between the Ng and B atoms in HNgBO and Ng and O atoms in the HNgOAl molecules. In addition, the charge distribution and atoms-in-molecules (AIM) analyses are in agreement with the above-mentioned conclusion and also suggest that the predicted metastable HNgBO and HNgOAl molecules should essentially exist in the form of [HNg]⁺[BO]^- and [HNg]⁺[OAl]^-, respectively. All the calculated results reported in this work indicate that it might be possible to prepare and characterize the predicted molecules via suitable experimental technique(s) under cryogenic conditions.

Noble gas hydrides in the triplet state: HNgCCO+ (Ng = He, Ne, Ar, Kr, and Xe)

Motivated by the very recent investigations of neutral noble gas compounds in the open-shell configuration, we explored a new series of noble gas hydrides in the triplet state. The possible existence of noble gas-inserted ketenyl cations, HNgCCO+ (Ng = He, Ne, Ar, Kr, and Xe), in their triplet electronic state has been predicted by various ab initio quantum chemical techniques. Density functional theory (DFT), second-order Møller-Plesset perturbation theory (MP2), and coupled-cluster theory (CCSD(T)) based methods have been employed to investigate the structures, energetics, harmonic vibrational frequencies, and charge distribution analysis of these ions. The aforementioned ions have been found to be thermodynamically stable with respect to all plausible 2-body and 3-body dissociation channels, except the 2-body dissociation pathway leading to the formation of global minima products (Ng + HCCO+). Nevertheless, each of the predicted HNgCCO+ ions is connected to the global minima products through a transition state with a finite barrier height on the potential energy surface, which confirms the kinetic stability of the metastable species. Detailed analysis of the optimized structural parameters, energetics, and harmonic vibrational frequencies of the predicted species clearly indicated that a strong covalent bond exists between H and Ng atoms, while a comparatively weak interaction is found between Ng and C atoms. Moreover, charge distribution and atoms-in-molecules (AIM) analysis strongly concurred with the above inferences and also suggested that the predicted metastable ions should exist essentially in the form of [HNg]+[CCO] complex. These results ultimately indicate that these predicted species may be prepared and characterized by suitable experimental technique(s) under a cryogenic environment.

Cyanide-isocyanide isomerization: stability and bonding in noble gas inserted metal cyanides (metal = Cu, Ag, Au)

The internal isomerization, MNC ↔ MCN (M = Cu, Ag, Au), is investigated through quantum chemical computations. CuNC and AgNC are shown to be neither thermochemically nor kinetically stable against transformation to MCN. The free energy barrier (ΔG‡) for AuNC is somewhat considerable (7.1 kcal mol-1), indicating its viability, particularly at low temperature. Further, the Ng inserted analogues, MNgCN (M = Cu, Ag, Au; Ng = Xe, Rn) turn out to be thermochemically stable with respect to all possible dissociation channels but for two two-body dissociation channels, viz., MNgCN → Ng + MCN and MNgCN → Ng + MNC, which are connected to the internal isomerization processes, MNgCN → NgMCN and MNgCN → NgMNC, respectively. However, they are kinetically protected by substantial ΔG‡ values (11.8-15.4 kcal mol-1 for Cu, 9.8-13.6 kcal mol-1 for Ag, and 19.7-24.7 kcal mol-1 for Au). The pathways for such internal conversion are explored in detail. A thorough inspection of the bonding situation of the studied molecules, employing natural bond order, electron density, adaptive natural density partitioning, and energy decomposition analyses indicates that the M-Ng bonds in MNgCN and Ng-C bonds in AuNgCN can be represented as an electron-shared covalent bond. For the other Ng-C bonds, although an ionic description is better suited, the degree of covalent character is also substantial therein.

Compounds with Rare Gas-Selenium/Tellurium Bonds: A Theoretical Investigation on FRgLF n and FRgLF n-1+ (Rg = Kr-Rn, L = Se and Te, n = 1, 3, and 5)

A new type of interesting insertion compounds FRgLF _n (Rg = Kr-Rn, L = Se and Te, n = 1, 3 and 5) and ionic FRgLF _n-1⁺ obtained through the insertion of a rare gas atom into the selenium fluorides and tellurium fluorides have been explored theoretically using MP2, CCSD(T), and PBE0 calculations. These predicted species were examined to present the optimized geometries, vibrational modes, molecular properties, thermodynamic and kinetic stabilities and bond nature. The optimized structures are without imaginary frequencies and metastable. In neutral FRgLF _n, F-Rg bonds should be of ionic character with large dissociation energy ranging from 150-200 kcal mol^-1 that could be best described by F^-(RgLF _n)⁺. Rg-L bonds have some covalent character with lower interaction energies within the range 25-40 kcal mol^-1. In FRgL⁺ and FRgLF₂⁺, the bonding nature of the F-Rg and Rg-L bonds are somewhat similar to that of the neutral compounds. In FRgLF₄⁺, the F-Rg bond could be of partial covalent type but the Rg-L bond could be considered as an ionic bond.

An ab initio study on noble gas inserted halogenated acetylene: HNgCCX (Ng = Kr and Xe; X = halogen)

Although HNgCCX (Ng = Kr and Xe; X = F and Cl) have been identified in cryogenic matrices, similar Br and I analogues have not been prepared so far. In this paper, the nature of HNgCCX (Ng = Kr and Xe; X = F, Cl, Br and I) have been investigated by ab initio methods. The main characteristic absorption peak of HNgCCX is the v_H-Ng, which decreases as X varies from F to I. Moreover, the H-Xe bond is stronger than the H-Kr bond. The v_C≡C and v_C-X exhibit red- and blue-shift characters, respectively, especially the C-X bond is abnormal blue-shift halogen bond. AIM results show that the H-Ng bond is essentially covalent bond and the covalent character of H-Xe bond is underestimated, and the trend of the covalent character is C-Cl > C-Br > C-F > C-I. Although HNgCCX is instable thermodynamically with respect to Ng + HCCX, it is kinetically stable with respect to the two-/three-body channels due to the relatively larger energy barriers. The three-body channels of HNgCCX is the main decomposition channel, and the kinetically stability of HXeCCX is more than its Kr analogues. This study is helpful for the preparation of new HNgCCX in cryogenic matrices.

Matrix-isolation and theoretical study of the HXeCCXeH⋯HCCH and HXeCC⋯HCCH complexes

HXeCCXeH and HXeCC noble-gas hydrides complexed with acetylene.

Prediction of neutral noble gas insertion compounds with heavier pnictides: FNgY (Ng = Kr and Xe; Y = As, Sb and Bi)

Neutral noble gas insertion compounds involving arsenic, antimony and bismuth atoms wherein the triplet electronic state is the ground state are predicted for the first time.

Matrix-isolation and ab initio study of HKrCCCl and HXeCCCl

We report on two new noble-gas molecules, HKrCCCl and HXeCCCl, prepared in low-temperature Kr and Xe matrices. These molecules are made by UV photolysis of HCCCl in the matrices and subsequent thermal annealing. The HCCCl precursor is produced by microwave discharge of a mixture of a matrix gas with trichloroethylene (HClC=CCl2). The assignments of the new noble-gas molecules are supported by deuteration experiments and quantum chemical calculations at the MP2(full) and CCSD(T) levels of theory with the def2-TZVPPD basis set. No evidence of ClXeCCH, which is computationally reliably stable, is found in the experiments. ClKrCCH as well as the Ar compounds HArCCCl and ClArCCH are not observed either, which is in agreement with the calculations.

Noble-Gas-Inserted Fluoro(sulphido)boron (FNgBS, Ng = Ar, Kr, and Xe): A Theoretical Prediction

The possibility of the existence of a new series of neutral noble gas compound, FNgBS (where Ng = Ar, Kr, Xe), is explored theoretically through the insertion of a Ng atom into the fluoroborosulfide molecule (FBS). Second-order Møller-Plesset perturbation theory, density functional theory, and coupled cluster theory based methods have been employed to predict the structure, stability, harmonic vibrational frequencies, and charge distribution of FNgBS molecules. Through energetics study, it has been found that the molecules could dissociate into global minima products (Ng + FBS) on the respective singlet potential energy surface via a unimolecular dissociation channel; however, the sufficiently large activation energy barriers provide enough kinetic stability to the predicted molecules, which, in turn, prevent them from dissociating into the global minima products. Moreover, the FNgBS species are thermodynamically stable, owing to very high positive energies with respect to other two two-body dissociation channels, leading to FNg + BS and F(-) + NgBS(+), and two three-body dissociation channels, corresponding to the dissociation into F + Ng + BS and F(-) + Ng + BS(+). Furthermore, the Mulliken and NBO charge analysis together with the AIM results reveal that the Ng-B bond is more of covalent in nature, whereas the F-Ng bond is predominantly ionic in character. Thus, these compounds can be better represented as F(-)[NgBS](+). This fact is also supported by the detail analysis of bond length, bond dissociation energy, and stretching force constant values. All of the calculated results reported in this work clearly indicate that it might be possible to prepare and characterize the FNgBS molecules in cryogenic environment through matrix isolation technique by using a mixture of OCS/BF3 in the presence of large quantity of noble gas under suitable experimental conditions.

Vibrational energy levels of difluorodioxirane computed with variational and perturbative methods from a hybrid force field

We have computed vibrational energy levels of difluorodioxirane (CF2O2). For the potential, a Taylor expansion in normal coordinates is used. The CCSD(T) and MP2 methods and correlation consistent basis sets of quadruple-zeta quality are used to determine the force constants. The vibrational Schrödinger equation was solved using both a variational method and second order perturbation theory. The Watson kinetic energy operator and a discrete variable representation were used with the DEWE (E. Mátyus, G. Czakó, B.T. Sutcliffe and A.G. Császár, J. Chem. Phys. 127 (2007) 084102) computer program to do the variational calculations. For the variational calculations, the average absolute deviation of fundamentals, with respect to experimental values, is less than 3 cm(-1). Perturbative results are almost as good. About 300 vibrational levels were computed. (16)O→(18)O isotopic shifts have also been calculated variationally for the lowest 75 vibrational energy levels and are compared to experimental results.

Predicted organic compounds derived from rare gas atoms and formic acid

Organic insertion compounds of rare gas atoms into formic acid were investigated at the MP2(full)/aug-cc-pVTZ level. There are two configuration isomers for each molecule based on the location of H atoms: trans- and cis-HCOORgH (Rg = Ar, Kr, Xe). Their structures, harmonic frequencies, and decomposition energies have been calculated using the above ab initio method. Using trans-HCOOXeH as an example, natural bond orbital (NBO) and atom-in-molecules (AIM) analyses were also carried out to explore the binding nature of the rare gas atoms. The formation mechanism of molecular orbitals is also presented in this paper. The presented results indicate that HCOOXeH and HCOOKrH are potential candidates for experimental observation.

Theoretical prediction of XRgCO(+) ions (X = F, Cl, and Rg = Ar, Kr, Xe)

In this work we have predicted novel rare gas containing cationic molecules, XRgCO(+) (X = F, Cl and Rg = Ar, Kr, Xe) using ab initio quantum chemical methods. Detail structural, stability, vibrational frequency, and charge distribution values are reported using density functional theory, second-order Møller-Plesset perturbation theory, and coupled-cluster theory based methods. These ions are found to be metastable in nature and exhibit a linear geometry with C∞v symmetry in their minima energy structures, and the nonlinear transition state geometries are associated with Cs symmetry. Except for the two-body dissociation channel (Rg + XCO(+)), these ions are stable with respect to all other dissociation channels. However, the connecting transition states between the above-mentioned two-body dissociation channel products and the predicted ions are associated with sufficient energy barriers, which restricts the metastable species to transform into the global minimum products. Thus, it may be possible to detect and characterize these metastable ions using an electron bombardment technique under cryogenic conditions.

In quest of strong Be-Ng bonds among the neutral Ng-Be complexes

The global minimum geometries of BeCN2 and BeNBO are linear BeN-CN and BeN-BO, respectively. The Be center of BeCN2 binds He with the highest Be-He dissociation energy among the studied neutral He-Be complexes. In addition, BeCN2 can be further tuned as a better noble gas trapper by attaching it with any electron-withdrawing group. Taking BeO, BeS, BeNH, BeNBO, and BeCN2 systems, the study at the CCSD(T)/def2-TZVP level of theory also shows that both BeCN2 and BeNBO systems have higher noble gas binding ability than those related reported systems. ΔG values for the formation of NgBeCN2/NgBeNBO (Ng = Ar-Rn) are negative at room temperature (298 K), whereas the same becomes negative at low temperature for Ng = He and Ne. The polarization plus the charge transfer is the dominating term in the interaction energy.

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.

Basis set effects in simple compounds of heavy rare gases

Rare-gas hydrides of the type HRgX (Rg = Xe or Rn and X = F, Cl, Br, or I) have been studied using Møller–Plesset and density functional theory methods. Six model core potentials and their associated basis sets were used, with relativistic effects included implicitly. The effects of polarization, correlating, and diffuse basis functions were investigated. Molecular geometries of the metastable hydrides and transition states along the decomposition pathway were computed together with corresponding energies of formation and decomposition. The results of quantum theory of atoms in molecules analysis further elucidate the interactions between atoms in HRgX species and confirm the results of analyses obtained from the natural bond orbitals approach.

Ab initio study of the organic xenon insertion compound into ethylene and ethane

This paper studies Xe-insertion ethylene and ethane compounds, i.e., HXeC2H3 and HXeC2H5. The structures, harmonic frequencies, and energetics for both molecules have been calculated at the MP2(full)/6-311++G(2d,2p) level. Our theoretical results predict the existence of HXeC2H3 and the instability of HXeC2H5. Natural bond orbital (NBO) analysis shows a strong ionic bond between the xenon atom and hydrocarbon radical. In addition, the interaction between the donor (Xe lone pair) and acceptor (the C-C antibonding orbital, i.e., π*(C-C)) increases the stability of HXeC2H3.

Theoretical prediction on the structures and stability of the noble-gas containing anions FNgCC- (Ng=He, Ar, Kr, and Xe)

We have made high-level theoretical study on a new type of noble-gas (Ng) containing anions FNgCC(-). The calculated short Ng-CC bond lengths of 1.13, 1.77, 1.89, and 2.04 Å for Ng=He, Ar, Kr, and Xe, respectively, and the electron density distributions indicated strong covalent interactions between the Ng and CC induced by the polarizing fluoride ion. Except for FHeCC(-), the structures of all other FNgCC(-) were predicted to be linear. The intrinsic stability of the FNgCC(-) was studied by calculating the energies of the three-body dissociation reaction: FNgCC(-) → F(-) + Ng + CC and by calculating the energy barriers of the two-body dissociation reaction: FNgCC(-) → Ng + FCC(-). The results showed that FNgCC(-) (Ng=Ar, Kr, Xe) could be kinetically stable in the gas phase with the three-body dissociation energies of 17, 37, and 64 kcal/mol and two body-dissociation barriers of 22, 31, and 42 kcal/mol, respectively, at the coupled-cluster single double (triple)/aug-cc-pVQZ level of theory. The structures and the stability were also confirmed using the multi-reference CASPT2 calculation. Future experimental identification of the FNgCC(-) anions is expected under cryogenic conditions.

Theoretical investigation of rare gas hydride cations: HRgN2+ (Rg=He, Ar, Kr, and Xe)

Rare gas containing protonated nitrogen cations, HRgN(2)(+) (Rg=He, Ar, Kr, and Xe), have been predicted using quantum computational methods. HRgN(2)(+) ions exhibit linear structure (C(∞v) symmetry) at the minima and show planar structure (C(s) symmetry) at the transition state. The stability is determined by computing the energy differences between the predicted ions and its various unimolecular dissociation products. Analysis of energy diagram indicates that HXeN(2)(+) is thermodynamically stable with respect to dissociated products while HHeN(2)(+), HArN(2)(+), and HKrN(2)(+) ions are metastable with small barrier heights. Moreover, the computed intrinsic reaction coordinate analysis also confirms that the minima and the 2-body global dissociation products are connected through transition states for the metastable ions. The coupled-cluster theory computed dissociation energies corresponding to the 2-body dissociation (HN(2)(+) + Rg) is -288.4, -98.3, -21.5, and 41.4 kJ mol(-1) for HHeN(2)(+), HArN(2)(+), HKrN(2)(+), and HXeN(2)(+) ions, respectively. The dissociation energies are positive for all the other channels implying that the predicted ions are stable with respect to other 2- and 3-body dissociation channels. Atoms-in-molecules analysis indicates that predicted ions may be best described as HRg(+)N(2). It should be noted that the energetic of HXeN(2)(+) ion is comparable to that of the experimentally observed stable mixed cations, viz. (RgHRg')(+). Therefore, it may be possible to prepare and characterize HXeN(2)(+) ions in an electron bombardment matrix isolation technique.