The H3O Rydberg radical

A convenient set of vibrational coordinates for 2D calculation of the tunneling splittings of the ground state and some excited vibrational states for the inversion motion in H3O+, H3O-, and H3O

Splitting of the ground state and some excited symmetric bending vibrational states due to inversion tunneling of the oxygen atom in the H₃O⁺, H₃O^- ions and in the H₃O radical are analyzed by numerically solving the vibrational Schrödinger equation of restricted (2D) dimensionality. As two vibrational coordinates, we used 1) the distance of the oxygen atom from the plane of a regular triangle formed by three hydrogen atoms and 2) a symmetry coordinate composed of three distances between chemically non-bonded hydrogen atoms. The kinetic energy operator in this case takes the simplest form. The 2D potential energy surface (PES) in the given coordinates was calculated for H₃O⁺ at the CCSD(T)/aug-cc-pVTZ and CCSD(T)-F12/cc-pVTZ-F12 levels of theory. The same 2D PES for the H₃O^- anion and H₃O radical were calculated at the CCSD(T)/aug-cc-pVQZ, CCSD(T)/d-aug-cc-pVQZ and UCCSD(T)/aug-cc-pVQZ, UCCSD(T)/d-aug-cc-pVQZ levels of theory, respectively. The tunneling splittings were calculated for the cations H₃¹⁶O⁺, D₃¹⁶O⁺, T₃¹⁶O⁺, H₃¹⁸O⁺, D₃¹⁸O⁺, T₃¹⁸O⁺. The tunneling splittings for the H₃O^-, D₃O^-, T₃O^- anions and H₃O, D₃O, T₃O radicals were calculated for the first time. The results of calculations demonstrate good agreement with experimental values of the tunneling splittings in the ground state and in some excited vibrational states of the H₃¹⁶O⁺ and D₃¹⁶O⁺ cations.

Superalkali Coated Rydberg Molecules

A series of complexes of Na, K, NH4, and H3O with [bpy.bpy.bpy]cryptand, [2.2.2]cryptand, and spherical cryptand were investigated via DFT and ab initio methods. We found that by coating Rydberg molecules with the "organic skin" one could further decrease their ionization potential energy, reaching the values of ∼1.5 eV and a new low record of 1.3 eV. The neutral cryptand complexes in this sense possess a weakly bounded electron and may be considered as very strong reducing agents. Moreover, the presence of an organic cage increases the thermodynamic stability of Rydberg molecules making them stable toward the proton detachment.

Electron binding energies and Dyson orbitals of OnH2n+1 +,0,- clusters: Double Rydberg anions, Rydberg radicals, and micro-solvated hydronium cations

Ab initio electron propagator methods are employed to predict the vertical electron attachment energies (VEAEs) of OH₃ ⁺(H₂O)_n clusters. The VEAEs decrease with increasing n, and the corresponding Dyson orbitals are diffused over exterior, non-hydrogen bonded protons. Clusters formed from OH₃ ^- double Rydberg anions (DRAs) and stabilized by hydrogen bonding or electrostatic interactions between ions and polar molecules are studied through calculations on OH₃ ^-(H₂O)_n complexes and are compared with more stable H^-(H₂O)_n+1 isomers. Remarkable changes in the geometry of the anionic hydronium-water clusters with respect to their cationic counterparts occur. Rydberg electrons in the uncharged and anionic clusters are held near the exterior protons of the water network. For all values of n, the anion-water complex H^-(H₂O)_n+1 is always the most stable, with large vertical electron detachment energies (VEDEs). OH₃ ^-(H₂O)_n DRA isomers have well separated VEDEs and may be visible in anion photoelectron spectra. Corresponding Dyson orbitals occupy regions beyond the peripheral O-H bonds and differ significantly from those obtained for the VEAEs of the cations.

Ultrafast Dynamics of Water Radiolysis: Hydrated Electron Formation, Solvation, Recombination, and Scavenging

The ultrafast formation, solvation, and geminate recombination of hydrated electrons upon vacuum ultraviolet photoexcitation of liquid water and the static and dynamic scavenging by NO₃^- are investigated using femtosecond time-resolved photoelectron spectroscopy. The solvation time constant for excess electrons is typical of that for liquid water but increases slightly with increasing excitation energy. The electron survival probability for geminate recombination is found to be much lower than the literature values owing to previously unobserved ultrafast geminate recombination in a period of 5 ps. NO₃^- induces the ultrafast (static) scavenging of photoexcited electronic states of liquid water and the dynamic scavenging of detached electrons with a reaction rate that is dependent on the excitation energy. The formation of hydrated electrons at 7.7 eV is ascribed to a H-atom-transfer process, but it is plausible that additional formation channels open at higher energies.

Vibrational excitation and product branching ratios in dissociation of the isotopologs of H3O: experiment and theory

The dissociation dynamics of the Rydberg radical H3O and the deuterated isotopologs have been studied by dissociative charge exchange of H3O(+) with Cs. Center-of-mass kinetic energy release distributions were measured with a fast-beam translational spectrometer and compared with direct dynamics quasiclassical trajectory calculations with initial conditions from an ab initio potential energy surface for H3O(+). The experimental branching fractions for dissociation of each isotopolog were obtained and compared with the calculated branching fractions. The dominant dissociation channel for all species is elimination of an H/D atom, and the water product was formed with a significant vibrational inversion in stretching vibrations that varies with the mass of the leaving atom in the dissociation. Branching fractions for the mixed isotopologs show that H atom elimination is favored over D atom elimination. Given the importance of H3O(+) in plasmas, astrochemistry, and in condensed phases, the striking energy partitioning found in this neutralization process is notable.

Hot water molecules from dissociative recombination of D3O+ with cold electrons

Individual product channels in the dissociative recombination of deuterated hydronium ions and cold electrons are studied in an ion storage ring by velocity imaging using spatial and mass-sensitive detection of the neutral reaction fragments. Initial and final molecular excitation are analyzed, finding the outgoing water molecules to carry internal excitation of more than 3 eV in 90% of the recombination events. Initial rotation is found to be substantial and in three-body breakup strongly asymmetric energy repartition among the deuterium products is enhanced for hot parent ions.

The reduction of water clusters H+(H2O)n to (OH-)(H2O)m by double electron transfer from Cs atoms

(H(+))(H(2)O)(n) ions (n = 1-72) at 50 keV energies were brought to collide with caesium atoms. The analysis of the products formed for clusters having n > 4 shows that this leads to the formation of a population of (OH(-))(H(2)O)(m) ions with a variable number m. On average, more than half of the water molecules are lost from the cluster in the process. A model can explain the experimental observations where two successive collisions occur within a time period of less than 100 ns. One-electron transfer from caesium to water leading to the loss of one hydrogen atom occurs at each stage. While the first stage is by itself exothermic, the second stage requires additional energy from collisional energy transfer.

Excited state properties of liquid water

In this paper, we give an overview of the state of the art in calculations of the electronic band structure and absorption spectra of water. After an introduction to the main theoretical and computational schemes used, we present results for the electronic and optical excitations of water. We focus mainly on liquid water, but spectroscopic properties of ice and vapor phase are also described. The applicability and the accuracy of first-principles methods are discussed, and results are critically presented.

Ground and excited states of the Rydberg radical H3O: Electron propagator and quantum defect analysis

Vertical excitation energies of the Rydberg radical H(3)O are inferred from ab initio electron propagator calculations on the electron affinities of H(3)O(+). The adiabatic ionization energy of H(3)O is evaluated with coupled-cluster calculations. These predictions provide optimal parameters for the molecular-adapted quantum defect orbital method, which is used to determine oscillator strengths. Given that the experimental spectrum of H(3)O does not seem to be available, comparisons with previous calculations are discussed. A simple model Hamiltonian, suitable for the study of bound states with arbitrarily high energies is generated by these means.