Ayan Ghosh

Theoretical prediction of noble gas inserted thioformyl cations: HNgCS⁺ (Ng = He, Ne, Ar, Kr, and Xe).

The existence of new interesting insertion compounds, HNgCS(+) (Ng = He-Xe), have been predicted theoretically through insertion of a noble gas atom into the thioformyl cation, HCS(+). Second-order Møller-Plesset perturbation theory (MP2), density functional theory (DFT), and coupled-cluster theory (CCSD(T)) based techniques have been used to explore the structure, energetics, charge distribution, and harmonic vibrational frequencies of these compounds. These predicted ions are found to be energetically stable with respect to all the possible 2-body and 3-body dissociation pathways, except the 2-body channel leading to the global minimum products (HCS(+) + Ng). Nevertheless, all these ions are found to be kinetically stable with a finite barrier height corresponding to their transition states, which are connected to their respective global minima products. The results obtained from charge distribution as well as atoms in molecules (AIM) analysis suggest that these ions can be best described as [HNg](+)CS. Strong covalent character in the H-Ng bond is supported by the high positive energy value corresponding to the 3-body dissociation pathways. Thus, it might be possible to prepare the HNgCS(+) ions in a glow discharge containing H2S, CO, and noble gas under cryogenic conditions through matrix isolation technique.

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 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.

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.

Prediction of a Neutral Noble Gas Compound in the Triplet State

Discovery of the HArF molecule associated with H-Ar covalent bonding [Nature, 2000, 406, 874-876] has revolutionized the field of noble gas chemistry. In general, this class of noble gas compound involving conventional chemical bonds exists as closed-shell species in a singlet electronic state. For the first time, in a bid to predict neutral noble gas chemical compounds in their triplet electronic state, we have carried out a systematic investigation of xenon inserted FN and FP species by using quantum chemical calculations with density functional theory and various post-Hartree-Fock-based correlated methods, including the multireference configuration interaction technique. The FXeP and FXeN species are predicted to be stable by all the computational methods employed in the present work, such as density functional theory (DFT), second-order Møller-Plesset perturbation theory (MP2), coupled-cluster theory (CCSD(T)), and multireference configuration interaction (MRCI). For the purpose of comparison we have also included the Kr-inserted compounds of FN and FP species. Geometrical parameters, dissociation energies, transition-state barrier heights, atomic charge distributions, vibrational frequency data, and atoms-in-molecules properties clearly indicate that it is possible to experimentally realize the most stable state of FXeP and FXeN molecules, which is triplet in nature, through the matrix isolation technique under cryogenic conditions.

Unprecedented Enhancement of Noble Gas–Noble Metal Bonding in NgAu3+ (Ng = Ar, Kr, and Xe) Ion through Hydrogen Doping

Behavior of gold as hydrogen in certain gold compounds and a very recent experimental report on the noble gas-noble metal interaction in Ar complexes of mixed Au-Ag trimers have motivated us to investigate the effect of hydrogen doping on the Ng-Au (Ng = Ar, Kr, and Xe) bonding through various ab initio based techniques. The calculated results show considerable strengthening of the Ng-Au bond in terms of bond length, bond energy, stretching vibrational frequency, and force constant. Particularly, an exceptional enhancement of Ar-Au bonding strength has been observed in ArAuH2+ species as compared to that in ArAu3+ system, as revealed from the CCSD(T) calculated Ar-Au bond energy value of 32 and 72 kJ mol-1 for ArAu3+ and ArAuH2+, respectively. In the calculated IR spectra, the Ar-Au stretching frequency is blue-shifted by 65% in going from ArAu3+ to ArAuH2+ species. Similar trends have been obtained in the case of all Ar, Kr, and Xe complexes with Ag and Cu trimers. Among all the NgM3-kHk+ complexes (where k = 0-2), the strongest binding in NgMH2+ complex is attributed to significant enhancement in the covalent characteristics of the Ng-M bond and considerable increase in charge-induced dipole interaction, as shown from the topological analysis.

Noble Gas Inserted Protonated Silicon Monoxide Cations: HNgOSi(+) (Ng = He, Ne, Ar, Kr, and Xe).

The existence of noble gas containing protonated silicon monoxide complexes have been predicted theoretically through ab initio quantum chemical methods. The predicted HNgOSi(+) ions are obtained by insertion of a noble gas atom (Ng = He, Ne, Ar, Kr, and Xe) between the H and O atoms in SiOH(+) ion. The structural parameters, energetics, harmonic vibrational frequencies, and charge distributions have been analyzed by optimizing the minima and the transition state structures using second-order Møller-Plesset perturbation theory (MP2), density functional theory (DFT), and coupled-cluster theory (CCSD(T)) based techniques. The predicted HNgOSi(+) ions are found to be stable with respect to all possible 2-body and 3-body dissociation channels, except the dissociation path leading to the respective global minimum products. However, these ions are found to be kinetically stable with respect to the global minimum dissociation process as revealed from the finite barrier heights, which in turn can prevent the transformation of these metastable species to the global minimum products. Furthermore, the computed bond lengths, vibrational frequencies, and force constant values suggest that a strong covalent bond exists between the H and Ng atoms in HNgOSi(+) ions while the Ng and O atoms share a strong van der Waals kind of interaction. Charge distributions and bonding analysis indicate that HNgOSi(+) ions can be best represented as strong complexes between the [HNg](+) ions and OSi molecule. All the computational results suggest that the predicted species, HNgOSi(+), may be prepared and characterized by suitable experimental technique at cryogenic temperature.