Addition of water, methanol, and ammonia to Al3O3- clusters: reaction products, transition states, and electron detachment energies

Products of reactions between the book and kite isomers of Al3O3- and three important molecules are studied with electronic structure calculations. Dissociative adsorption of H2O or CH3OH is highly exothermic and proton-transfer barriers between anion-molecule complexes and the products of these reactions are low. For NH3, the reaction energies are less exothermic and the corresponding barriers are higher. Depending on experimental conditions, Al3O3- (NH3) coordination complexes or products of dissociative adsorption may be prepared. Vertical electron detachment energies of stable anions are predicted with ab initio electron propagator calculations and are in close agreement with experiments on Al3O3- and its products with H2O and CH3OH. Changes in the localization properties of two Al-centered Dyson orbitals account for the differences between the photoelectron spectra of Al3O3- and those of the product anions.     

Sequential addition of H2O, CH3OH, and NH3 to Al3O3-: a theoretical study

Photoelectron spectra of two species, Al3O3(H2O)2- and Al3O3(CH3OH)2-, that are produced by the addition of two water or methanol molecules to Al3O3- are interpreted with density-functional geometry optimizations and electron propagator calculations of vertical electron detachment energies. In both cases, there is only one isomer that is responsible for the observed spectral features. A high barrier to the addition of a second molecule may impede the formation of Al3O3N2H6- clusters in an analogous experiment with NH3.     

Products of the addition of water molecules to Al3O3- clusters: structure, bonding, and electron binding energies in Al3O4H2-, Al3O5H4-, Al3O4H2, and Al3O5H4

Two stable products of reactions of water molecules with the Al3O3- cluster, Al3O4H2- and Al3O5H4-, are studied with electronic structure calculations. There are several minima with similar energies for both anions and the corresponding molecules. Dissociative absorption of a water molecule to produce an anionic cluster with hydroxide ions is thermodynamically favored over the formation of Al3O3-(H2O)n complexes. Vertical electron detachment energies of Al3O4H2- and Al3O5H4- calculated with ab initio electron propagator methods provide a quantitative interpretation of recent anion photoelectron spectra. Contrasts and similarities in these spectra may be explained in terms of the Dyson orbitals associated with each transition energy.     

Global potential energy surfaces for O((3)P) + H2O((1)A1) collisions

Global analytic potential energy surfaces for O((3)P) + H(2)O((1)A(1)) collisions, including the OH + OH hydrogen abstraction and H + OOH hydrogen elimination channels, are presented. Ab initio electronic structure calculations were performed at the CASSCF + MP2 level with an O(4s3p2d1f)/H(3s2p) one electron basis set. Approximately 10(5) geometries were used to fit the three lowest triplet adiabatic states corresponding to the triply degenerate O((3)P) + H(2)O((1)A(1)) reactants. Transition state theory rate constant and total cross section calculations using classical trajectories to collision energies up to 120?kcal mol(-1) (～11?km s(-1) collision velocity) were performed and show good agreement with experimental data. Flux-velocity contour maps are presented at selected energies for H(2)O collisional excitation, OH + OH, and H + OOH channels to further investigate the dynamics, especially the competition and distinct dynamics of the two reactive channels. There are large differences in the contributions of each of the triplet surfaces to the reactive channels, especially at higher energies. The present surfaces should support quantitative modeling of O((3)P) + H(2)O((1)A(1)) collision processes up to ～150?kcal mol(-1).     

A theoretical and computational study of the anion, neutral, and cation Cu(H(2)O) complexes

An ab initio investigation of the potential energy surfaces and vibrational energies and wave functions of the anion, neutral, and cation Cu(H(2)O) complexes is presented. The equilibrium geometries and harmonic frequencies of the three charge states of Cu(H(2)O) are calculated at the MP2 level of theory. CCSD(T) calculations predict a vertical electron detachment energy for the anion complex of 1.65 eV and a vertical ionization potential for the neutral complex of 6.27 eV. Potential energy surfaces are calculated for the three charge states of the copper-water complexes. These potential energy surfaces are used in variational calculations of the vibrational wave functions and energies and from these, the dissociation energies D(0) of the anion, neutral, and cation charge states of Cu(H(2)O) are predicted to be 0.39, 0.16, and 1.74 eV, respectively. In addition, the vertical excitation energies, that correspond to the 4 (2)P<--4 (2)S transition of the copper atom, and ionization potentials of the neutral Cu(H(2)O) are calculated over a range of Cu(H(2)O) configurations. In hydrogen-bonded, Cu-HOH configurations, the vertical excitation and ionization energies are blueshifted with respect to the corresponding values for atomic copper, and in Cu-OH(2) configurations where the copper atom is located near the oxygen end of water, both quantities are redshifted.     

Computational study on the negative electron affinities of NO2 -.(H2O)n clusters (n=0-30)

Here we report negative electron affinities of NO(2)(-).(H2O)n clusters (n=0-30) obtained from density functional theory calculations and a simple correction to Koopmans' theorem. The method relies on the calculation of the detachment energy of the monoanion and its highest occupied molecular orbital and lowest unoccupied molecular orbital energies, and explicit calculations on the dianion itself are avoided. A good agreement with resonances in the cross section for neutral production in electron scattering experiments is found for n=0, 1, and 2. We find several isomeric structures of NO(2)(-).(H2O)2 of similar energy that elucidate the interplay between water-water and ion-water interactions. The topology is predicted to influence the electron affinity by 0.5 and 0.4 eV for NO(2)(-).(H2O) and NO(2)(-).(H2O)2, respectively. The electron affinity of larger clusters is shown to follow a (n+delta)-1/3 dependence, where delta=3 represents the number of water molecules that in volume, could replace NO(2) (-).     

Photochemistry of water: the (H2O)5 cluster

The structures of the cyclic water pentamer, the H3O+(H2O)3OH- zwitterion, and the H3O(H2O)3OH biradical form of the (H2O)5 cluster have been determined with the second-order M?ller-Plesset method and with density-functional theory (DFT). The vertical singlet excitation energies of these structures have been calculated with the second-order approximated coupled-cluster method and with time-dependent DFT, respectively. The molecular and electronic structures of the H3O(H2O)3OH biradical have been characterized for the first time. The lowest electronic states of the biradical are slightly lower in energy than the vertically excited states of the covalent and zwitterionic (H2O)5 clusters and therefore are photochemically accessible from the latter. The electronic absorption spectrum of the biradical exhibits the characteristic features of the absorption spectrum of the hydrated electron. It is argued that the basic mechanisms of the photochemistry of water, in particular the generation of the hydrated electron by UV photons, can be unraveled by relatively straightforward electronic structure and dynamics calculations for finite-size water clusters.     

Empty level structure in phenyl and benzyl isocyanates

The energies of the lowest-lying anion states of phenyl (C6H5N=C=O) and benzyl (C6H5CH2N=C=O) isocyanates have been determined experimentally in the gas phase for the first time using electron transmission spectroscopy (ETS), and their localization properties have been evaluated using HF/6-31G, MP2/6-31G*, and B3LYP/6-31G* calculations. The lowest-lying anion state of phenyl isocyanate, mainly of benzene ring character but with some contribution also from the N=C=O pi-system, lies at significantly higher energy than that of other benzenes substituted by pi-functionals, such as benzaldehyde or styrene. The scaling with the use of suitable empirical equations of the virtual orbital energies (VOEs) for orbitals with predominantly pi*(ring) character calculated for the neutral-state molecules leads to vertical attachment energies (VAEs) which closely correspond to those determined experimentally, whereas those calculated for the predominantly pi*(CO) and pi*(NC) orbitals (3rd and 4th LUMO, respectively) are significantly different from the corresponding measured values notwithstanding the fact that the calculations reproduce the shortening of the N=C and C=O double bonds.     

Molecular dynamics investigation of ferrous-ferric electron transfer in a hydrolyzing aqueous solution: calculation of the pH dependence of the diabatic transfer barrier and the potential of mean force

We present a molecular model for ferrous-ferric electron transfer in an aqueous solution that accounts for electronic polarizability and exhibits spontaneous cation hydrolysis. An extended Lagrangian technique is introduced for carrying out calculations of electron-transfer barriers in polarizable systems. The model predicts that the diabatic barrier to electron transfer increases with increasing pH, due to stabilization of the Fe3+ by fluctuations in the number of hydroxide ions in its first coordination sphere, in much the same way as the barrier would increase with increasing dielectric constant in the Marcus theory. We have also calculated the effect of pH on the potential of mean force between two hydrolyzing ions in aqueous solution. As expected, increasing pH reduces the potential of mean force between the ferrous and ferric ions in the model system. The magnitudes of the predicted increase in diabatic transfer barrier and the predicted decrease in the potential of mean force nearly cancel each other at the canonical transfer distance of 0.55 nm. Even though hydrolysis is allowed in our calculations, the distribution of reorganization energies has only one maximum and is Gaussian to an excellent approximation, giving a harmonic free energy surface in the reorganization energy F(DeltaE) with a single minimum. There is thus a surprising amount of overlap in electron-transfer reorganization energies for Fe(2+)-Fe(H2O)6(3+), Fe(2+)-Fe(OH)(H2O)5(2+), and Fe(2+)-Fe(OH)2(H2O)+ couples, indicating that fluctuations in hydrolysis state can be viewed on a continuum with other solvent contributions to the reorganization energy. There appears to be little justification for thinking of the transfer rate as arising from the contributions of different hydrolysis states. Electronic structure calculations indicate that Fe(H2O)6(2+)-Fe(OH)n(H2O)(6-n)(3-n)+ complexes interacting through H3O2- bridges do not have large electronic couplings.     

MULTIMODE quantum calculations of intramolecular vibrational energies of the water dimer and trimer using ab initio-based potential energy surfaces

We report vibrational configuration interaction calculations of the monomer fundamentals of (H(2)O)(2), (D(2)O)(2), (H(2)O)(3), and (D(2)O)(3) using the code MULTIMODE and full dimensional ab initio-based global potential energies surfaces (PESs). For the dimer the HBB PES [Huang et al., J. Chem. Phys 128, 034312 (2008)] is used and for the trimer a new PES, reported here, is used. The salient properties of the new trimer PES are presented and compared to previous single-point calculations and the vibrational energies are compared with experiments.     

OH(3) (-) and O(2)H(5) (-) double Rydberg anions: predictions and comparisons with NH(4) (-) and N(2)H(7) (-)

A low barrier in the reaction pathway between the double Rydberg isomer of OH(3) (-) and a hydride-water complex indicates that the former species is more difficult to isolate and characterize through anion photoelectron spectroscopy than the well known double Rydberg anion (DRA), tetrahedral NH(4) (-). Electron propagator calculations of vertical electron detachment energies (VEDEs) and isosurface plots of the electron localization function disclose that the transition state's electronic structure more closely resembles that of the DRA than that of the hydride-water complex. Possible stabilization of the OH(3) (-) DRA through hydrogen bonding or ion-dipole interactions is examined through calculations on O(2)H(5) (-) species. Three O(2)H(5) (-) minima with H(-)(H(2)O)(2), hydrogen-bridged, and DRA-molecule structures resemble previously discovered N(2)H(7) (-) species and have well separated VEDEs that may be observable in anion photoelectron spectra.     

Theoretical study of the red‐ and blue‐shifted hydrogen bonds of nitroxyl and acetylene dimers

Ab initio molecular orbital and density functional theory (DFT) in conjunction with different basis sets calculations were performed to study the C? H…O red‐shifted and N? H…π blue‐shifted hydrogen bonds in HNO? C₂H₂ dimers. The geometric structures, vibrational frequencies and interaction energies were calculated by both standard and counterpoise (CP)‐corrected methods. In addition, the G3B3 method was employed to calculate the interaction energies. The topological and natural bond orbital (NBO) analysis were investigated the origin of N? H…π blue‐shifted hydrogen bond. From the NBO analysis, the electron density decrease in the σ* (N? H) is due to the significant electron density redistribution effect. The blue shifts of the N? H stretching frequency are attributed to a cooperative effect between the rehybridization and electron density redistribution. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

Ab initio and density functional theory reinvestigation of gas-phase sulfuric acid monohydrate and ammonium hydrogen sulfate

We have calculated the thermochemical parameters for the reactions H(2)SO(4) + H(2)O <--> H(2)SO(4).H(2)O and H(2)SO(4) + NH(3) <--> H(2)SO(4).NH(3) using the B3LYP and PW91 functionals, MP2 perturbation theory and four different basis sets. Different methods and basis sets yield very different results with respect to, for example, the reaction free energies. A large part, but not all, of these differences are caused by basis set superposition error (BSSE), which is on the order of 1-3 kcal mol(-1) for most method/basis set combinations used in previous studies. Complete basis set extrapolation (CBS) calculations using the cc-pV(X+d)Z and aug-cc-pV(X+d)Z basis sets (with X = D, T, Q) at the B3LYP level indicate that if BSSE errors of less than 0.2 kcal mol(-1) are desired in uncorrected calculations, basis sets of at least aug-cc-pV(T+d)Z quality should be used. The use of additional augmented basis functions is also shown to be important, as the BSSE error is significant for the nonaugmented basis sets even at the quadruple-zeta level. The effect of anharmonic corrections to the zero-point energies and thermal contributions to the free energy are shown to be around 0.4 kcal mol(-1) for the H(2)SO(4).H(2)O cluster at 298 K. Single-point CCSD(T) calculations for the H(2)SO(4).H(2)O cluster also indicate that B3LYP and MP2 calculations reproduce the CCSD(T) energies well, whereas the PW91 results are significantly overbinding. However, basis-set limit extrapolations at the CCSD(T) level indicate that the B3LYP binding energies are too low by ca. 1-2 kcal/mol. This probably explains the difference of about 2 kcal mol(-1) for the free energy of the H(2)SO(4) + H(2)O <--> H(2)SO(4).H(2)O reaction between the counterpoise-corrected B3LYP calculations with large basis sets and the diffusion-based experimental values of S. M. Ball, D. R. Hanson, F. L Eisele and P. H. McMurry (J. Phys. Chem. A. 2000, 104, 1715). Topological analysis of the electronic charge density based on the quantum theory of atoms in molecules (QTAIM) shows that different method/basis set combinations lead to qualitatively different bonding patterns for the H(2)SO(4).NH(3) cluster. Using QTAIM analysis, we have also defined a proton transfer degree parameter which may be useful in further studies.     

Electron binding energies and Dyson orbitals of Al5Om- (m=3,4,5) and Al5O5H2-

Photoelectron spectra of Al(5)O(m)(-) (m=3-5) and of the anion produced by the dissociative adsorption of a water molecule by Al(5)O(4)(-) are interpreted with density-functional geometry optimizations and electron-propagator calculations of vertical electron detachment energies. For Al(5)O(3)(-), Al(5)O(4)(-), and Al(5)O(5)H(2)(-), the observed signals may be attributed to the most stable isomer of each anion. For Al(5)O(5)(-), the features in the photoelectron spectrum are due to three almost isoenergetic isomers.     

Generation and characterization of ionic and neutral P(OH) 2 +/. in the gas phase by tandem mass spectrometry and computational chemistry

The bicoordinated dihydroxyphosphenium ion P(OH)2+ (1+) was generated specifically by charge-exchange dissociative ionization of triethylphosphite and its connectivity was confirmed by collision induced dissociation and neutralization-reionization mass spectra. The major dissociation of 1+ forming PO+ ions at m/z 47 involved another isomer, O=P-OH2+ (2+), for which the optimized geometry showed a long P-OH2 bond. Dissociative 70-eV electron ionization of diethyl phosphite produced mostly 1+ together with a less stable isomer, HP(O)OH+ (3+). Ion 2+ is possibly co-formed with 1+ upon dissociative 70-eV electron ionization of methylphosphonic acid. Neutralization-reionization of 1+ confirmed that P(OH)2* (1) was a stable species. Dissociations of neutral 1, as identified by variable-time measurements, involved rate-determining isomerization to 2 followed by fast loss of water. A competitive loss of H occurs from long-lived excited states of 1 produced by vertical electron transfer. The A and B states undergo rate-determining internal conversion to vibrationally highly excited ground state that loses an H atom via two competing mechanisms. The first of these is the direct cleavage of one of the O-H bonds in 1. The other is an isomerization to 3 followed by cleavage of the P-H bond to form O=P-OH as a stable product. The relative, dissociation, and transition state energies for the ions and neutrals were studied by ab initio and density functional theory calculations up to the QCISD(T)/6-311+G(3df,2p) and CCSD(T)/aug-cc-pVTZ levels of theory. RRKM calculations were performed to investigate unimolecular dissociation kinetics of 1. Excited state geometries and energies were investigated by a combination of configuration interaction singles and time-dependent density functional theory calculations.     

Reactions of hydrated electrons (H2O)n- with carbon dioxide and molecular oxygen: hydration of the CO2- and O2- ions

The gas-phase reactions of hydrated electrons with carbon dioxide and molecular oxygen were studied by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. Both CO2 and O2 react efficiently with (H2O)n- because they possess low-lying empty pi* orbitals. The molecular CO2- and O2- anions are concurrently solvated and stabilized by the water ligands to form CO2(-)(H2O)n and O2(-)(H2O)n. Core exchange reactions are also observed, in which CO2(-)(H2O)n is transformed into O2(-)(H2O)n upon collision with O2. This is in agreement with the prediction based on density functional theory calculations that O2(-)(H2O)n clusters are thermodynamically favored with respect to CO2(-)(H2O)n. Electron detachment from the product species is only observed for CO2(-)(H2O)2, in agreement with the calculated electron affinities and solvation energies.     

Are structures with Al-H bonds represented in the photoelectron spectrum of Al3O4H2-?

Photoelectron spectra of Al3O4H2- clusters formed by reactions of Al3O3- with water molecules have been interpreted recently in terms of dissociative absorption products with hydroxide and oxide anions that are coordinated to aluminum cations. Alternative isomers with Al-H bonds have lower energies, but barriers to hydrogen migrations that break O-H bonds and create Al-H bonds are high. Ab initio electron propagator calculations of the vertical electron detachment energies of the anions indicate that the species with hydrides cannot be assigned to the chief features in the photoelectron spectrum. Therefore, the previously studied dissociative absorption products are the structures that are most likely to be probed in the photoelectron spectra.     

Experimental and theoretical studies of charge transfer and deuterium ion transfer between D2O+ and C2H4

The charge transfer and deuterium ion transfer reactions between D(2)O(+) and C(2)H(4) have been studied using the crossed beam technique at relative collision energies below one electron volt and by density functional theory (DFT) calculations. Both direct and rearrangement charge transfer processes are observed, forming C(2)H(4) (+) and C(2)H(3)D(+), respectively. Independent of collision energy, deuterium ion transfer accounts for approximately 20% of the reactive collisions. Between 22 and 36 % of charge transfer collisions occur with rearrangement. In both charge transfer processes, comparison of the internal energy distributions of products with the photoelectron spectrum of C(2)H(4) shows that Franck-Condon factors determine energy disposal in these channels. DFT calculations provide evidence for transient intermediates that undergo H/D migration with rearrangement, but with minimal modification of the product energy distributions determined by long range electron transfer. The cross section for charge transfer with rearrangement is approximately 10(3) larger than predicted from the Rice-Ramsperger-Kassel-Marcus isomerization rate in transient complexes, suggesting a nonstatistical mechanism for H/D exchange. DFT calculations suggest that reactive trajectories for deuterium ion transfer follow a pathway in which a deuterium atom from D(2)O(+) approaches the pi-cloud of ethylene along the perpendicular bisector of the C-C bond. The product kinetic energy distributions exhibit structure consistent with vibrational motion of the D-atom in the bridged C(2)H(4)D(+) product perpendicular to the C-C bond. The reaction quantitatively transforms the reaction exothermicity into internal excitation of the products, consistent with mixed energy release in which the deuterium ion is transferred in a configuration in which both the breaking and the forming bonds are extended.     

Quantum vibrational analysis of hydrated ions using an ab initio potential

We present full-dimensional potential energy surfaces (PESs) for hydrated chloride based on the sum of ab initio (H(2)O)Cl(-), (H(2)O)(2), and (H(2)O)(3) potentials. The PESs are shown to predict minima and corresponding harmonic frequencies accurately on the basis of comparisons with previous and new ab initio calculations for (H(2)O)(2)Cl(-), (H(2)O)(3)Cl(-), and (H(2)O)(4)Cl(-). An estimate of the effect of the 3-body water interaction is made using a simple 3-body water potential that was recently fit to tens of thousands of ab initio 3-body energies. Anharmonic, coupled vibrational calculations are presented for these clusters, using the "local monomer model" for the high frequency intramolecular modes. This model is tested against previous "exact" calculations for (H(2)O)Cl(-). Radial distribution functions at 0 K obtained from quantum zero-point wave functions are also presented for the (H(2)O)(2)Cl(-) and (H(2)O)(3)Cl(-) clusters.     

取代基对1-甲基尿嘧啶与N-甲基乙酰胺氢键复合物中氢键强度的影响

使用密度泛函理论B3LYP方法和二阶微扰理论MP2方法对由1-甲基尿嘧啶与N-甲基乙酰胺所形成的氢键复合物中的氢键强度进行了理论研究, 探讨了不同取代基取代氢键受体分子1-甲基尿嘧啶中的氢原子对氢键强度的影响和氢键的协同性. 研究表明: 供电子取代基使N－H…O＝C氢键键长r(H…O)缩短, 氢键强度增强; 吸电子取代基使N－H…O＝C氢键键长r(H…O)伸长, 氢键强度减弱. 自然键轨道(NBO)分析表明: 供电子基团使参与形成氢键的氢原子的正电荷增加, 使氧原子的负电荷增加, 使质子供体和受体分子间的电荷转移量增多; 吸电子基团则相反. 供电子基团使N－H…O＝C氢键中氧原子的孤对电子轨道n(O)对N－H的反键轨道σ^*(N－H)的二阶相互作用稳定化能增强, 吸电子基团使这种二阶相互作用稳定化能减弱. 取代基对与其相近的N－H…O＝C氢键影响更大.