Surface S(N)2 reaction by H2O on chlorinated Si(100)-2 x 1 surface

The potential energy surfaces of one, two, and three water molecule sequential adsorptions on the symmetrically chlorinated Si(100)-2 x 1 surface were theoretically explored with SIMOMM:MP2/6-31G(d). The first water molecule adsorption to the surface dimer requires a higher reaction barrier than the subsequent second water molecule adsorption. The lone pair electrons of the incoming water molecule nucleophilically attack the surface Si atom to which the leaving Cl group is bonded, yielding an S(N)2 type transition state. At the same time, the Cl abstracts the H atom of the incoming water molecule, forming a unique four-membered ring conformation. The second water molecule adsorption to the same surface dimer requires a much lower reaction barrier, which is attributed to the surface cooperative effect by the surface hydroxyl group that can form a hydrogen bond with the incoming second water molecule. The third water molecule adsorption exhibits a higher reaction barrier than the first and the second water molecule adsorption channels but yields a thermodynamically more stable product. In general, it is expected that the surface Si-Cl bonds can be subjected to the substitution reactions by water molecules, yielding surface Si-OH bonds, which can be a good initial template for subsequent surface chemical modifications. However, oversaturations can be a competing side reaction under severe conditions, suggesting that the precise control of surface kinetic environments is necessary to tailor the final surface characteristics.     

Ni(115)台阶面对氢表面微观动力学行为的影响

用５参数Ｍｏｒｓｅ势模拟氢－镍表面体系相互作用势，考察了氢原子在Ｎｉ（１１５）台面上吸附扩散行为。同时构造了氢分子与Ｎｉ（１００）和Ｎｉ（１１５）台阶面 相互作用推广的ＬＥＰＳ势面面，考察了氢分子解离化学吸附的微观动力学性质。     

THEORY OF GAS-PHASE ACIDITY(Ⅰ)CORRELATION OF DEPROTONATION ENERGY WITH HYDROGEN CHARGE

The charge distributions of various acids and their conjugate bases are calculated by using CNDO/2 and MNDO with full geometry optimization.The deprotonation energy is found to be better correlated with the charge on the acidic hydrogen than with the charge on the atom linking to the hydrogen and with the charge on the nucleophilic atom of the conjugate base.This shows that the charge on the acidic hydrogen has an important effect on acidity,whereas the effect of the charge on the linking atom and on the nucleophilic atom of the conjugate base is not important.It can thus be deduced that the view of stabilization of the anio'n due to dispersion of the negative charge is not a significant explanation of acidity.     

气相酸性理论(Ⅰ)——脱质子能与氢电荷的相关

采用半经验自洽场法中的cNDO/2法和MNDO法作全几何优化,计算了多种酸及其共轭碱的电荷分布。考察了气相酸的脱质子能实验数据与酸性氢原子以及相连原子和共轭碱亲核原子的电荷,表明前者相关性比后两者好得多。说明酸性氢原子上的电荷是影响酸性的重要因素,而后两者并不重要。由此推断电荷分散使负离子趋于稳定的观点不能成为酸性规律的主要解释。     

Investigation of organosilicon radicals : I. Methylphenylsilane anion radicals

CNDO/2 calculations with an spd basis set have been carried out on methyl-phenylsilane anion radicals, and the calculated spin density values compared with the experimental hyperfine coupling constants. The CNDO method overestimates the role of d orbitals and the partial charges on hydrogen atoms attached to silicon atom. The partial charge distribution and the carbonsilicon bond order in the anion radicals and the corresponding neutral molecules are discussed. The equilibrium carbonsilicon bond distance in the trimethylphenylsilane molecule and corresponding anion radical have also been investigated.     

外型-1,4-氧桥-环己基-2,3-二羧酸的晶体及分子结构

外型-1,4-氧桥-环己基-2,3-二羧酸晶体属单斜晶系,空间群为P2_1/n;晶胞参数为:α=5.594(3)A,b=11.178(7)A,c=14.675(11)A,β=91.46(5)°;Ζ=4.从直接法得到结构的初始模型,经块矩阵最小二乘修正后,最后的R值为0.072.在晶体中,分子间的O—H…O氢键将分子连接成层型氢键体系.使用自编的CNDO/2程序,计算得电子的能量、分子的总能量、偶极矩及各原子的电荷密度和净电荷.     

甲醇在催化剂MgO（100）面上吸附的量子化学研究

本文用ＣＮＤＯ／２半经验最子化学计算方法对ＣＨ３ＯＨ分子在（ＭｇＯ）４（１００）面上的２８种可能的吸附态进行了优化计算，得到以ＣＨ３ＯＨ分子中－ＣＨ３取向吸附在（ＭｇＯ）４（１００）面的Ｏ＾－原子上，且为重叠式构型最稳态。此构型中由于－ＣＨ３上的三个氢原子形成结构适应的三氢正电集团与氧的静电作用的结果。从吸附态的能量及Ｍｕｌｌｉｋｅｎ集居数上分析得甲醇在ＭｇＯ催化剂上有利于形成ＣＨ４和ＣＯ，这一结     

Potential energy surfaces for the interaction of hydrogen atoms with beryllium metal clusters

With a modified CNDO/2 molecular orbital approach, potential energy surfaces are computed for the attack of beryllium atom clusters simulating “smooth” (0001) and “corrugated” (1010) faces of beryllium metal. Several stable sites for chemisorption are found with binding energies of 40–55 kcal/mole, but penetration of the lattice appears possible at some points. Results are compared with the preliminary ab initio predictions of Bauschlicher, Liskow, Bender and Schaefer.     

CNDO/2 calculations of relaxation and reconstruction of diamond and silicon [111] surfaces

CNDO /2 calculations have been performed on the clusters X₄H₉ and X₄Y₉ modeling the [111] diamond and silicon surfaces. The X is either carbon or silicon atom and the Y is a pseudoatom containing one sp³ hybrid orbital. It is shown that in the CNDO /2 approximation in the foregoing pseudoatom models, the charge distribution of the cluster is better than the hydrogen atom, because the electronegativity of the hydrogen differs significantly from the electronegativity of the sp² orbital of the silicon atom. Using the CNDO /2 parametrization, the electronegativity of the hydrogen is very near to the electronegativity of the sp³ orbital of the carbon atom, thus the hydrogen can be used for the saturation of the carbon clusters.     

甲醇和氨对腺嘌呤水解脱氨机理的影响(英文)

用密度泛函理论在B3LYP/6-311G(d,p)水平上研究了甲醇和氨辅助的腺嘌呤水解脱氨机理,结果表明该反应首先是在水的亲核进攻下形成一个四面体结构中间体,然后该中间体通过构象变化得到两个不同构象,从而找到两条不同反应路径.在路径a中,辅助分子参与了过渡态的形成,起到转移氢原子的作用;而在路径b中,辅助分子仅作为介质,没有参与过渡态的形成.在氨辅助的情况下,腺嘌呤在亲核反应前发生了胺-亚胺异构化,而在甲醇辅助机理中则未发生该异构化.能量结果表明甲醇辅助腺嘌呤脱氨反应具有与水辅助类似的势垒,而氨辅助反应的势垒则比水辅助的高.     

H~2S对硫酸溶液中铁腐蚀作用的CNDO/2研究

动电位扫描得出工业纯铁在含H~2S的H~2SO~4溶液中腐蚀的电化学行为。应用CNDO/2法确定了阴、阳极电位下H~2S,HS^-在金属Fe晶面上的稳定吸附取向与最佳吸附间距,通过对吸附物总能量、结合能、净电荷分布的计算,得出H~2S体系阴、阳极反应被加速的微观机制。阳极电位下,大量HS^-为S原子的平行吸附方式,HS^-负电荷大部分向Fe转移,促进铁的溶解。阴极电位下,少量H~2S则为H原子的平行吸附方式,Fe表面负电荷向H~2S分子中与Fe作用的H转移,促进析氢。在CNDO/2法计算的基础上,圆满地解释了实验结果。     

Reactivity of isomeric pyridinecarboxaldehydes in catalyic hydrogenation

It has been established by a quantum-chemical method (CNDO/2) that there are two possible mechanisms occurring in the vapor phase hydrogenation of 2-, 3-, and 4-pyridinecarboxaldehydes in the presence of a copper-chromium catalyst at 180-300°C. One of these involves a donor-acceptor interaction of aldehyde with catalyst and the addition of hydrogen to the carbon atom of the carbonyl group at the first stage. The second possible mechanism is the synchronous addition of hydrogen to the carbon and oxygen of the carbonyl group of a weakly bound a aldehyde molecule with an unchanged electronic structure.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1082–1086, August, 1994.     

Ab initio Mechanism Study on the Reaction of Chlorine Atom with Formic Acid

The potential energy surface(PES) for the reaction of Cl atom with HCOOH is predicted using ab initio molecular orbital calculation methods at UQCIDS(T,full)6-311 G(3df,2p)//UMP2(full)/6-311 G(d,P) level of theory with zero-point vibrational energy (ZPVE) correction.The calculated results show that the reaction mechanism of Cl atom with formic acid is a C-site hydrogen abstraction reaction from cis-HOC(H)O molecule by Cl atom with a 3.73kJ/mol reaction barrier height,leading to the formation of cis-HOCO radical which will reacts with Cl atom or other molecules in such a reaction system.Because the reaction barrier height of O-site hydrogen abstraction reaction from cis-HOC(H)O molecule by Cl atom which leads to the formation of HCO2 radical is 67.95kJ/mol,it is a secondary reaction channel in experiment,This is in good agreement with the prediction based on the previous experiments.     

氢在Ni(511)台阶面的吸附与解离研究

The adsorption and dissociation of hydrogen on stepped surface (511) of nickel are studied with the embedded-atom model (EAM) method. The adsorption energy, the length of the adsorption bond and the adsorption height for a single hydrogen atom are calculated. Three kinds of stable sites are found for hydrogen adsorption. There are the double-fold bridge site B on the step edge, the three-fold hollow site H3′ on the step surface and the four-fold hollow sites H1 and H2 on the terrace surface. Compared with a hydrogen atom adsorbed on low-index (001) surface, there are two other adsorption sites near the step: the two-fold bridge site B on the step edge and the three-fold hollow site H3′ on the step surface. At the same time, the absorbability of the hydrogen atom at the site H1 is intensified. The results show that hydrogen adsorption on Ni (511) is affected by the existence of the step. The active barriers, adsorption energy and corresponding bond length for dissociation of a hydrogen molecule on the stepped surface are presented. The results show that the dissociation is easier at the bottom of the step. It is shown that the steps are the active sites for hydrogen adsorption and dissociation.     

Enhancement of hydrogen physisorption on graphene and carbon nanotubes by Li doping

Density-functional calculations of the adsorption of molecular hydrogen on a planar graphene layer and on the external surface of a (4,4) carbon nanotube, undoped and doped with lithium, have been carried out. Hydrogen molecules are physisorbed on pure graphene and on the nanotube with binding energies about 80-90 meV/molecule. However, the binding energies increase to 160-180 meV/molecule for many adsorption configurations of the molecule near a Li atom in the doped systems. A charge-density analysis shows that the origin of the increase in binding energy is the electronic charge transfer from the Li atom to graphene and the nanotube. The results support and explain qualitatively the enhancement of the hydrogen storage capacity observed in some experiments of hydrogen adsorption on carbon nanotubes doped with alkali atoms.     

CNDO/2 and INDO calculations of a reaction pathway for the sigmatropic [1, 5] H-shift in cyclopentadiene

CNDO/2 and INDO calculations have been carried out in order to construct a suitable model for the activated complex during the reaction. In this reaction model the migrating hydrogen atom moves along an edge of the cyclopentadiene ring. An analysis of this situation suggests a partial electron transfer from the migrating hydrogen to the nascent cyclopentadienyl system. This charge transfer is discussed in terms of aromaticity. The calculated activation enthalpies are 10 kcal/mole (CNDO/2) and 17 kcal/mole (INDO), whereas the experimental value is ca. 24 kcal/mole [1].     

Correlated proton motion in hydrogen bonded systems: tuning proton affinities

The theorem of matching proton affinities (PA) has been widely used in the analysis of hydrogen bonds. However, most experimental and theoretical investigations have to cope with the problem that the variation of the PA of one partner in the hydrogen bond severely affects the properties of the interface between both molecules. The B3LYP/d95+(d,p) analysis of two hydrogen bonds coupled by a 5-methyl-1H-imidazole molecule showed that it is possible to change the PA of one partner of the hydrogen bond while maintaining the properties of the interface. This technique allowed us to correlate various properties of the hydrogen bond directly with the difference in the PAs between both partners: it is possible to tune the potential energy surface of the bonding hydrogen atom from that of an ordinary hydrogen bond (localized hydrogen atom) to that of a low barrier hydrogen bond (LBHB, delocalized hydrogen atom) just by varying the proton affinity of one partner. This correlation shows clearly that matching PAs are of lesser importance for the formation of a LBHB than the relative energy difference between the two tautomers of the hydrogen bond.     

Quantum-chemical modeling of the hydrogen spillover effect in the H/Pt/SnO<Subscript>2</Subscript> system

The hydrogen migration over the surface of platinum clusters applied to the tin dioxide crystal surface has been modeled by the density functional theory method within the generalized gradient approximation (GGA) under periodic conditions using a projector-augmented plane-wave (PAW) basis set with a pseudopotential. It has been demonstrated that the dissociative adsorption energy of a hydrogen molecule onto the Pt₁₉ cluster surface is 1.6 eV. The movement of the hydrogen atom over the cluster surface is ∼0.4 eV more favorable than in the bulk. The location of the hydrogen atom on the SnO₂ substrate is 1.62 eV more favorable than that on the upper face of the Pt₁₉ cluster. The barriers to migration of hydrogen atom over the surface of the platinum cluster applied to the SnO₂ surface are within 0.1–0.2 eV.     

A Theoretical Study of the Interaction of Hydrogen and Oxygen with Palladium or Gold Adsorbed on Pyridine‐Like Nitrogen‐Doped Graphene

The interaction of H₂ and O₂ molecules in the presence of nitrogen‐doped graphene decorated with either a palladium or gold atom was investigated by using density functional theory. It was found that two hydrogen molecules were adsorbed on the palladium atom. The interaction of these adsorbed hydrogen molecules with two oxygen molecules generates two hydrogen peroxide molecules first through a Eley–Rideal mechanism and then through a Langmuir–Hinshelwood mechanism. The barrier energies for this reaction were small; therefore, we expect that this process may occur spontaneously at room temperature. In the case of gold, a single hydrogen molecule is adsorbed and dissociated on the metal atom. The interaction of the dissociated hydrogen molecule on the surface with one oxygen molecule generates a water molecule. The competitive adsorption between oxygen and hydrogen molecules slightly favors oxygen adsorption.     

亚甲基自由基(3CH2)与SO反应机理的理论研究

白洪涛,黄旭日,于广涛,李吉来,于健康,孙家钟. 亚甲基自由基(3CH2)与SO反应机理的理论研究[J]. 化学学报, 2006, 64(2): 139-144.