Double-differential ionization cross-section for H2O

First results are presented for the doubly differential ionization cross-section at 0° of water vapor by positrons with an incident energy of 100 eV. Fragmentation paths are also identified.     

A basis set comparison in a variational scheme for the Yukawa potential

The variational method is used to obtain solutions to Schrödinger's equation for a particle in the radially screened Yukawa potential. A basis set is presented. While the Laguerre basis set shows considerable improvement over the hydrogenic one, problems are still encountered as the screening parameter approaches its threshold value. Variational calculations are also presented using an Eckart-type basis set which looks promising near the critical screening region.     

Some valence bond calculations for H2 with 1s and 2p basis sets

Summary The results ofab initio valence bond calculations are reported for H₂, with up to 16 nuclear centred and eight midbond 1s and 2p AOs included in them. The 24 AO calculation, with 116S=0 spin structures, gives an STO-6G energy of –1.17237 a.u., which is close to an MP4 estimate of –1.17256 a.u.     

Selection of a quantum-chemical method and basis set for optimization of the complex ion Cu(H2O)+

Calculations of the open-shell van der Waals complex Cu(H₂O)⁺ were carried out at 15 theoretical levels basing on the DFT theory in its variants B3LYP and BLYP. Five types of basis function were used (3-21G*, 3-21G**, 6-31G(d,p), 6-311G(d,p) and CEP-4G) each combined with one (+) or two (++) diffuse functions. The aim of the research was to find out the most accurate combination of method and basis set which predicts structural, energetic and vibration parameters closest to the experimentally found ones. Several experimental parameters were used as reference values.     

The basis set superposition error in multilevel methods: a test on the H2O and HF dimer

The basis set superposition error (BSSE) is often very important in the accurate calculation of dimerization energies. Accurate prediction of thermochemical properties requires appropriate consideration of the basis set incompleteness error. Multilevel methods introduce adjustable parameters to reproduce experimental data, that is, the higher level correction (HLC) in G3 and adjustable coefficients in the MCCM. However, the HLC term is cancelled out and the adjustable coefficients in the MCCM do not remove the BSSE completely. We have calculated the BSSE involved in the multilevel methods. The H₂O and HF dimer systems were used as a test case. This study shows that empirical coefficients do reduce the BSSE in some cases and an MCCM with good parameters can be used to reproduce dimerization energies within chemical accuracy without the BSSE correction.     

水分子垂直电离能的从头计算

分子的芯电子和价电子电离能可用XPS和UPS测得,并可作理论上的近似计算,其中ab initio Hartree-Fock SCF LCAO-MO法是目前广泛采用的一种方法.它所作的三个近似(非相对论近似、Born-Oppenheimer近似和单电子近似)很明确.除了几个基本物理常数外,不再引进任何参数.但是计算中选用的基函数对所得结果的精确度有较大影响.因此,常常需要以扩大的Slater型函数(STF)或Gaussian型函数(GTF)为基函数.由于所需计算的双电子积分的数目正比于基函数数目的四次方,这样就会使计算化费的计算机时间大大增     

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 investigation of the excited states of the H2O2 molecule

Ab initio calculations for a series of excited states of the H₂O₂ molecule have been performed in order to discuss some recent photofragmentation experiments with laser light. For understanding these experiments the direction of the transition moments is of great interest, as well as the possibility of a HOO…H fragmentation.     

A correlation-consistent basis set for Fe

 A series of correlation-consistent basis sets are developed for Fe. Our best computed ⁵F–⁵D separation in the Fe atom is in excellent agreement with experiment. Our best estimate for the FeCO D ₀ value is in good agreement with experiment. The ⁵Σ⁻–³Σ⁻ separation in FeCO has an error of 3.6 kcal/mol; while the origin of this error is not clear, it is probably not due to the basis set. Received: 5 March 2001 / Accepted: 2 May 2001 / Published online: 9 August 2001     

A flash photolysis resonance fluorescence investigation of the reaction OH + H2O2 → HO2 + H2O

The flash photolysis resonance fluorescence technique has been used to measure the rate constant for the reaction over the temperature range of 250–370 K. The present results are in excellent agreement with three very recent studies, and the combined data set can been used to derive the expression similar to that currently used in atmospheric modeling applications. A summary of our computer simulation of this reaction system is presented. The results of the computations indicate the absence of secondary reaction complications in the present work while revealing significant problems in the earlier (pre-1980) studies of the title reaction.     

A new oxygen sensitivity and its potential application in photosynthetic H2 production

We have discovered a new competitive pathway for O₂ sensitivity in algal H₂ production that is distinct from the O₂ sensitivity of hydrogenase per se. This O₂ sensitivity is apparently linked to the photosynthetic H₂ production pathway that is coupled to proton translocation across the thylakoid membrane. Addition of the proton uncoupler carbonyl cyanide-p-trifluoromethoxy-phenylhydrazone eliminates this mode of O₂ inhibition on H₂ photoevolution. This newly discovered inhibition is most likely owing to background O₂ that apparently serves as a terminal electron acceptor in competition with the H₂ production pathway for photosynthetically generated electrons from water splitting. This O₂-sensitive H₂ production electron transport pathway was inhibited by 3[3,4-dichlorophenyl]1,1-dimethylurea. Our experiments demonstrated that this new pathway is more sensitive to O₂ than the traditionally known O₂ sensitivity of hydrogenase. This discovery provides new insight into the mechanism of O₂ inactivation of hydrogenase and may contribute to the development of a more-efficient and robust system for photosynthetic H₂ production.     

Atmospheric pressure chemical ionization and fragmentation of aminomonosaccharides in H2O and D2O

Aminomonosaccharides (glucosamine, galactosamine, and mannosamine) in H₂O and D₂O were ionized by atmospheric pressure chemical ionization (APCI) and their fragmentation patterns were investigated to identify them. All the aminomonosaccharides showed the same fragment ions but their relative ion intensities were different. Major product ions generated in H₂O were [M + H]⁺, [M + H – H₂O]⁺, and [2M + H – 3H₂O]⁺, while in D₂O were [M_D6 + D]⁺, [M_D6 + D – D₂O]⁺, and [2M_D6 + D – D₂O – 2HDO]⁺. At a high fragmentor voltage above 120 V, the relative ion intensities of the major product ions showed different trends according to the aminomonosaccharides. For the use of H₂O as solvent and eluent, the order of the ion intensity ratio of [M + H – H₂O]⁺/[2M + H – 3H₂O]⁺ was galactosamine > mannosamine > glucosamine. When using D₂O as solvent and eluent, the order of the ion intensity ratios of [M_D6 + D – D₂O]⁺/[M_D6 + D]⁺ and [2M_D6 + D – D₂O – 2HDO]⁺/[M_D6 + D]⁺ was mannosamine > galactosamine > glucosamine. It was found that glucosamine, galactosamine, and mannosamine could be distinguished by the specific trends of the major product ion ratios in H₂O and D₂O. Copyright © 2009 John Wiley & Sons, Ltd.     

GF calculation with minimal and extended basis sets for H2O,NH3, CH4 and H2O2

A method is proposed for applying the theory of generalized group functions to SCF-GF calculations with large basis sets. A simple procedure for localising the SCF-MO's resulting from a standard SCF calculation is described, with applications to H₂O, NH₃, CH₄ and H₂O₂. Results compare quite favourably with those obtained by the usual GF method. It is shown that when basis functions are the SCF-MO's and there are only two functions per group, the GF approach is practically equivalent to a configuration interaction treatment where only double excitations within the groups are considered.

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Zusammenfassung Es wird eine Methode zur Anwendung von verallgemeinerten Gruppenfunktionen auf SCF-GF-Rechnungen mit großen Basissätzen vorgeschlagen. Ferner wird ein einfaches Verfahren zur Lokalisierung von SCF-MO's angegeben und auf H₂O, NH₃, CH₄ und H₂O₂ angewendet. Die Resultate sind denen üblicher GF-Methoden ähnlich. Wenn als Basisfunktionen SCF-Funktionen, und zwar nur zwei je Gruppe, angewendet werden, ist der GF-Ansatz praktisch einer CI-Rechnung mit maximal Zweifachanregungen äquivalent.

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Résumé On propose une méthode pour appliquer la théorie des fonctions de groupes généralisés à des calculs SCF GF dans des bases de grande dimension. Un procédé de localisation simple est décrit, il permet de localiser les orbitales SCF ordinaires et est appliqué à H₂O,NH₃, CH₄ et H₂O₂. Les résultats obtenus sont comparables à ceux fournis par la méthode GF ordinaire. Lorsque les fonctions de base sont les O.M. S.C.F. et qu'il n'y a que deux fonctions par groupe, la méthode GF est pratiquement équivalente à une interaction de configuration où seules seraient prises en considération les diexcitations à l'intérieur des groupes.

     

一个新的用于反应散射计算的L^2平动基函数集合

本文通过构造新的L^2平动基函数集合改进了Shima-Baer方法.新集合中不再含有任何人工可调参数,取而代之的是反应体系的分子特性常数.由于在平动基函数中含有在非经典区域内的高度衰减因子,从而大大提高了反应几率对平动基函数展开的收敛速度.对共线交换反应H+H~2→H~2+H的计算结果表果,对平均基函数展开的收敛速度已接近包含畸变势的计算结果.改进后的Shima-Baer方法计算量明显降低.     

Complete basis set ab initio computational study of ionization potential, electron affinity and the C-F bond dissociation energy for perfluorinated methane derivatives

A computational study of perfluorinated methane derivatives was performed with complete basis set ab initio methods. The total energies for their neutral, cation, and anionic states were computed. From these values, the energy gaps between different electronic states, ionization potentials, electron affinities, and C-F bond dissociation energies were calculated. The computed values are compared with experimental data and the reliability of complete basis set ab initio methods is discussed. New values for C-F bond dissociation energies are suggested. Received: 12 January 1998 / Accepted: 2 April 1998 / Published online: 29 July 1998     

A density functional investigation of the reaction mechanism of H2O + HCNO

A theoretical investigation of the H₂O + HCNO reaction, which is carried out by means of CCSD(T)/6‐311G(d,p)//B3LYP/6‐311G(d,p)+ZPVE computational method to determine a set of reasonable pathways, there are seven product pathways, P _i with i = 1 , 2 , …, 7 are involved. It is shown that P ₁ (H₂O + NCOH), P ₂ (CO + NH₂ + OH), P ₄ (HCN + HO₂ + H), and P ₆ (CO + NH₂OH) are the major product channels; and P ₇ (HOC + H₂ + NO) is the minor product channels, whereas the other channels for P ₃ (HNO + HCOH) and P ₅ (HNO + H₂CO) are very minor, the minor product channels. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

CEPA calculations of potential energy surfaces for open-shell systems.: IV. Photodissociation of H2O in the A1B1 state

A three-dimensional potential energy surface for the photodissociation of H₂O in its lowest excited singlet state $\text{A}$¹B₁ in C_2v or $\text{A}$¹A″ in C₃ symmetry, respectively, has been calculated with quantum-chemical ab initio methods including electron correlation. The main features of the surface are discussed and qualitative explanations are given for the experimentally observed vibrational and rotational excitations of the product OH(²Π) radicals. The surface will be used in subsequent investigations of the dynamics of the H₂O photodissociation process.