Proton solvated by noble-gas atoms: simplest case of a solvated ion

Abstract

The solvation of a proton by up to six rare-gas atoms He, Ne, Ar, Kr, and Xe is investigated by B3LYP density functional theory with large basis sets, forming the Ðrst systematic study of all rare gases, He through Xe, on the same high level of theory. The solvation energy for regular two-fold, trigonal planar, tetrahedral and octahedral coordination shows, as known previously, that the protonated rare gas dimer is the most stable conÐguration in every case. Solvation of a point charge by hard polarizable spheres yields the same preference for two-fold coordination. Two rare gas atoms shield the proton efficiently, and additional rare gas atoms may be coordinated in an equatorial plane or along the axis of the central protonated rare gas dimer, with binding energies and bond lengths comparable to those of the corresponding rare gas solids. The inÑuence of additional solvent atoms on the harmonic stretching frequencies is minor and cannot explain the large shift observed in low temperature matrices. Proton di †usion is examined by calculating the transition state for isomerization of species, which yields barrier heights of 8.8, 11.5, 29.7, 32.3, and 35.5 kJ mol~1 for He, Rg 3 HǸ e, Ar, Kr, and Xe, respectively. Geometries, harmonic frequencies, bond dissociation energies and partial charges of mixed protonated rare gas dimers reveal a consistently smooth trend of these properties with size and polarizability of the rare gas atoms. Based on these Ðndings, the assignment of spectral lines attributed to the mixed ArH`Kr, ArH`Xe, and KrH`Xe species is questioned. The stabilization of positive charge centers in solid Xe in the presence of hydrogen atoms is also discussed.

Infrared Identification of Proton-Bound Rare-Gas Dimers (XeHXe)+, (KrHKr)+, and (KrHXe)+ and Their Deuterated Species in Solid Hydrogen

“…41 For (XeHXe) + in solid Xe, the surrounding Xe atoms might compete for the proton with the two Xe atoms bound by the proton; a red shift from the value in the gaseous phase is expected. This condition is consistent with predicted harmonic vibrational wavenumbers of ν 3 , 800 cm −1 with the R-CCSD(T)/aug-cc-pVTZ-PP method in this work, 947 cm −1 with the B3LYP/6-311++G(3df,3pd)/SECP method, 5 and 834 cm −1 with the CCSD(T)/6-311++G(3df,3pd)/LJ18 method. 4 In contrast, Kr and Ar atoms compete less well with the two Xe atoms bound by the proton; the red shift of (XeHXe) + in solid Kr or Ar is thus insignificant.…”

“…5 Two rare-gas atoms shield the proton efficiently, and additional rare-gas atoms might be coordinated in an equatorial plane or along the axis of the central protonated rare-gas dimer, with binding energies and bond lengths comparable to those of the corresponding raregas solids. 5 Infrared spectra of these symmetric proton-bound dimers, (RgHRg) + , have been well characterized with a (nν 1 + ν 3 There is a tendency that the ν 3 fundamental vibrational wavenumber is greater in less polarizable media. If we take this tendency into account, the first doublets, 847.0 (832.3) cm −1 in p-H 2 and 844.7 (831.2) cm −1 in n-H 2 , can be assigned to the ν 3 fundamental vibration of (XeHXe) + isolated in two matrix sites of solid H 2 .…”

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

“…fundamental species in rare gas chemistry, and have been investigated extensively both theoretically as well as experimentally. [45][46][47][48][49] In fact, hydrohelium cation (HeH + ) is an important ion in astrochemistry, which was first observed in mass spectrometry 50 …”

Neutralization of solvated protons and formation of noble-gas hydride molecules: Matrix-isolation indications of tunneling mechanisms?

“…19 The energetics of this system allows the electron-tunneling process because the ͑NgHNg͒ + + e − neutralization reaction is strongly exothermic due to the large ionization energy of hydrogen ͑13.5 eV͒. The total solvation energy of a proton with two Ng atoms is computationally 4.4, 4.9, and 5.3 eV for Ar, Kr, and Xe, 32 respectively, and the electron affinity of Cl is 3.6 eV ͑the largest related value͒. The solvent reorganization energy, which results from the response of the medium to the change of the charge distribution between the initial and final states, and the electrostatic energy should also be considered; however, these contributions are not very large.…”