Theoretical treatment of IO-X (X = N2, CO, CO2, H2O) complexes.

Iodine monoxide (IO) is an important component of the biogeochemical cycle of iodine. For instance, it is present in the troposphere, where it plays a crucial role in the physical chemical processes involving iodine containing compounds. Here, we present a theoretical study on a series of atmospherically relevant complexes of IO with N2, CO, CO2 and H2O, where their structural and spectroscopic properties and their interaction energies are computed. Calculations are carried out by means of ab initio post Hartree-Fock (RCCSD(T) and RMP2) methods and density functional theory DFT (PBE0 and M05-2X) based approaches with and without the inclusion of dispersion correction. After comparison to RCCSD(T), we highlight the good performance of M05-2X(+D3) DFT in describing the bonding between IO and X (X = N2, CO, CO2, H2O). Moreover, we found that the IO-X (X = N2, CO, CO2, H2O) complexes are formed by non-covalent interactions between the two monomers. In sum, we characterized two types of complexes: I-bonded and O-bonded, where the former is more stable. The atmospheric implications of the present findings are also discussed such as in the formation of the iodine oxide particles (IOPs).

IO(X2Π)-Ar cluster: ab initio potential energy surface and dynamical computations.

Iodine oxide (IO) is an important tropospheric molecule. In the present paper, we mapped the potential energy surfaces (PESs) of the doubly degenerate IO(X2Π)-Ar van der Waals system using single- and double-excitation coupled cluster approaches with non-iterative perturbation treatment of triple excitations [RCCSD(T)] extrapolated to the complete basis set (CBS) limit. In addition to bent local minima, we identified a linear Ar-IO complex as a global minimum. Afterwards, we performed scattering calculations on these PESs, considering the non-zero spin-orbit contribution and the Renner-Teller effect. The integral cross-sections exhibit an oscillatory structure vs. the final rotational state, as already observed for the NO(X2Π)-Ar system. Moreover, computations reveal that the Ar-IO complex is stable toward dissociation into IO and Ar. Therefore, it can be found in the atmosphere and participates in iodine compound physical chemical processes occurring there.

Microsolvation of NO(+) in Ar(n) clusters: A theoretical treatment.

At present, we investigate the structure and the stability of NO(+)Arn (n ≤ 54) ionic clusters using analytical potential functions. The energy of these systems is described using additive potentials with VNO(+)Ar and VAr-Ar representing the pair potential interactions. To find the geometry of the lowest energy isomers of the NO(+)Arn clusters, we use the so-called basin hopping method of Wales et al. which combines a Monte-Carlo exploration and deformation method. The reliability of our model was checked by deriving the structures of the NO(+)Arn systems (n = 1, 2, 3 and 4) using ab initio Moller-Plesset perturbation theory up to second order (MP2) in connection with the aug-cc-pVTZ basis set. Magic numbers for sizes n = 8, 12, 18, 22, and 25 are found and they show a high relative stability. Our results reveal that a transition in the NO(+) ion coordination from 8 (square antiprism) to 12 (icosahedrons) occurs for n = 11. Examination of the stable structures of the ionic clusters demonstrates that the first solvation shell closes at n = 12. Furthermore, we found that the NO(+)Arn (n = 12-54) clusters are structurally very similar to the homogenous rare gas clusters with a polyicosahedral packing pattern. The distribution exhibits an additional magic number at n = 54, consistent with the completion of a second solvation sphere around NO(+). The effects of microsolvation of NO(+) cation in Ar clusters are also discussed. Generally, our results agree with the available experimental and theoretical findings on NO(+)Arn clusters and more generally on diatomics solvated in Ar clusters.

Theoretical investigations of the IO,q+ (q = 2, 3, 4) multi-charged ions: metastability, characterization and spectroscopy.

Using ab initio methodology, we studied the IO(q+) (q = 2, 3, 4) multi-charged ions. Benchmark computations on the IO(X(2)Π) neutral species allow validate the current procedure. For IO(2+), several potential wells were found on the ground and the electronic excited states potentials with potential barriers with respect to dissociation, where this dication can exist in the gas phase as long-lived metastable molecules. We confirm hence the recent observation of the dication by mass spectrometry. Moreover, we predict the existence of the metastable IO(3+) trication, where a shallow potential well along the IO internuclear distance is computed. This potential well supports more than 10 vibrational levels. The IO(3+) excited states are repulsive in nature, as well as the computed potentials for the IO(4+) tetracation. For the bound states, we give a set of spectroscopic parameters including excitation transition energies, equilibrium distances, harmonic and anharmonic vibrational terms, and rotational constants. At the MRCI + Q/aug-cc-pV5Z(-PP) level, the adiabatic double and triple ionization energies of IO are computed to be ~28.1 eV and ~55.0 eV, respectively.

Theoretical investigations of the electronic states of NaXe: a comparative study.

The electronic state properties of NaXe are investigated using ab initio methodologies and various pseudopotential approaches for comparison. The spectroscopic terms and dipole moments of the lowest electronic states up to the Na(3d) +Xe dissociation limit are determined. The difference between valence or smaller core pseudopotential on Xe is shown to be negligible and so is the difference between all-electron and valence pseudopotential completed by core-polarization treatments of Na. These calculations are used as references to test the performance of a treatment involving a zero electron pseudopotential description of xenon together with a one-electron pseudopotential description of Na. When compared with the reference calculations, the one-electron model leads to reasonable quantitative results. The potential energy curves and spectroscopic data of all Rydberg excited states of NaXe up the Na(5f)+Xe dissociation limit are determined using this method. Long distance wells and barriers in the range R = 15-40 bohrs are identified for some of the higher states with (2)Σ(+) symmetry.

Solvation of Na+ in argon clusters.

The structures and stabilities of Ar(n)Na+ clusters (n < or = 54) are investigated using atomistic potentials fitted to reproduce ab initio calculations performed at the coupled-cluster level on the smaller clusters. Polarization effects are described using either the interaction between dipoles induced by the sodium ion, or a small charge transfer in the framework of a fluctuating charges model. In both models, extra three-body contributions of the Axilrod-Teller type are also included between the sodium ion and all pairs of argon atoms. The two models predict essentially similar growth patterns, and a transition in the metal ion coordination from 8 (square antiprism) to 12 (icosahedron) is seen to occur near n = 50, in response to the intrasolvent constraints.