Møller-plesset calculations taking care of the correlation CUSP

Møller-Plesset calculations to second order have been carried out on the ten-electron systems Ne, HF and H₂O with a new functional, including r₁₂-dependent pair correlation functions, which takes care of the correlation cusp. The calculated second-order pair energies are accurate to within a few millihartree in comparison with the estimated exact values. In particular, second-order energies of 384.2, 380.1 and 362.9 mE_h, have been obtained for Ne, HF and H₂O respectively.     

Kinetics of Mn2O3 digestion in H2SO4 solutions

The kinetics of Mn₂O₃ digestion in various H₂SO₄ solutions (0.5-2.0 M) and at various temperatures (ambient to 80 °C) to form solid γ-MnO₂ and soluble Mn(II) have been examined using X-ray diffraction. Using a modified first-order Avrami expression to describe digestion kinetics, rate constants in the range 0.02-0.98 h⁻¹ were found for Mn₂O₃ disappearance, and 0.03-0.42 h⁻¹ for γ-MnO₂ formation, with higher H₂SO₄ concentrations and temperatures leading to faster conversion rates. Also, for a particular set of experimental conditions, the rate of γ-MnO₂ formation was always slower than Mn₂O₃ disappearance. This was interpreted in terms of the solubility and stability of the soluble Mn(III) intermediated formed during the digestion. Activation energies for Mn₂O₃ dissolution and γ-MnO₂ formation were also determined.     

Orientation and alignment of Mg+ (3p) states excited in 1–60 keV collisions with He and Ar

The orientation and alignment of Mg⁺ (3p) states created in 1–60 keV Mg⁺ (3s)-He, Ar collisions have been studied by the polarized photon-scattered particle coincidence technique at scattering angles corresponding to impact-parameter ranges of 0.5–1.0 a.u. (He) and 1.2–2.0 a.u. (Ar). Referring to the standard geometry, in the region of maximum excitation probability (～ 35 keV), a strong propensity for population of the Mg⁺ (3p _?1) state is observed. The propensity breaks down when going towards lower energies, and for collisions with He even a transient reversal of the angular momentum occurs. The alignment angle varies little in the entire range of impact parameters and energies investigated. These observations compare well with recent general predictions of Andersen and Nielsen.     

Tables of accurate STF HF wavefunctions from B to Ca

Accurate Slater type function (STF) Hartree-Fock (HF) wavefunctions are calculated and tabled from B to Ca. The STF's have a form of r ⁿ e ^-r and the powers (n) of r are carefully determined. The total atomic energies agree with those of numerical HF (NHF) within the error of 4×10^–6 a.u. and 1×10^–5 a.u. for B to F and for Ne to Ca, respectively. The STF HF basis sets given will be useful to benchmark calculations for the molecular, solid, and atomic electronic states. Applications of the STF HF basis to molecular calculations are given and briefly discussed. Sample calculations are performed on the N₂ and P₂ molecules.     

Ab initio calculations on H transfer in the HF trimer

Systematic ab initio LCAO MO calculations with basis sets of increasing size have been performed to analyze the changes in relative stabilization energies of the two cyclic (D_3h and C_3h symmetry) and the noncyclic HF trimers. The results form the basis for a discussion of cyclic H-transfer reactions.     

Ab initio valence bond calculations. VII. HF,HF+, and H2F+

Ab initio valence bond calculations for the ground and excited states of HF and HF⁺ are presented. Total energies, equilibrium geometries, dissociation energies, dipole moments, and spectroscopic constants for HF and HF⁺ have been calculated. The photoelectron spectrum of HF has been examined and interpreted by means of the valence bond formalism. The ground state of the protonated species H₂F⁺ has been investigated.     

Dielectric properties of novel poly(aryl prehnitimide)s

Six different variants of a new type of polyimide, poly(aryl prehnitimide)s, containing various moisture contents have been studied using dielectric relaxation spectroscopy. Dielectric loss measurements show the presence of a double peak near 200 K (depending on frequency) due to water relaxation. The two peaks have been designated γ₁ and γ₂. The γ₂ peak appears as a shoulder on the γ₁ peak at lower temperatures and is very sensitive to moisture content. The γ₁ peak is less sensitive to moisture content and is associated with isolated water molecules coupled to the polymer chains. Both of the γ-relaxation peaks were studied in detail to obtain the associated activation energies. © 1996 John Wiley & Sons, Inc.     

Basis-independent potential energy curves for the neutral diatomics of Li,Na and K evaluated by means of Hartree-Fock and different density functional potentials

Summary The solution of the Schrödinger equation for diatomic molecules when the finite element method is used gives the possibility to evaluate highly accurate basis-independent potential energy curves. In this work such types of numerically accurate potential energy curves on the HF level have been evaluated for Li₂, Na₂ and K₂ and could be used as benchmarks in the optimization of basis sets. A comparison between recent LCAO HF calculations in which extended basis sets are used and the accurate values determined in this work show that there is a difference in total energy of 4×10^–5 and 10^–3 a.u. for Li, Li₂, and Na, Na₂, respectively. Evaluated dissociation energies are, however, due to the cancellation of numerical errors in much better agreement. Further, it is found that different exchange correlation potentials for the heavier molecules such as those given by von Barth-Hedin and Vosko, Wilk and Nusair reproduce experimental properties such as dissociation energies, vibrational frequencies almost as well as those achieved with advanced CI methods. TheX potential gives accurate bond lengths for Na₂ and K₂, whereas the dissociation energies are too small.     

Experimental determination of the dissociation energies D0 and De of H2O…HF

The zero-point and equilibrium dissociation energies of the hydrogen-bonded dimer H₂O…HF have been determined as D₀ = 34.3(3) kJmol⁻¹ and D_e = 42.9 (8) kJmol⁻¹ from absolute intensities of rotational transitions in an equilibrium mixture of H₂O, HF and H₂O…HF.     

Theoretical study of the molecular ions SiH−5 and SiH−3

Ab initio HF and Cl calculations were performed to determine the equilibrium geometry of SiH^?₅ and SiH^?₃, the barrier for internal rotation (SiH^?₅) and inversion (SiH^?₃) and the stability of SiH^?₅ and further to study the effect of electron correlation on reaction energies. The gaussian-type basis included d and f functions on Si and a p set on II. The D_3h structures of SiH^?₅ is lower in energy than the C_4v structure by 2.9(3.2) kcal/mol (corresponding HF results in parentheses). SiH^?₃ has C_3v structure, the inner-ion barrier computed is 26.2 (27.3) kcal/mol. SiH^?₅ turns out to be stable with respect to SiH₄ + H^? by 20.3 (13.8) kcal/mol, but it is unstable with respect to SiH^?₃ ← H₂ by 6.3 (5.6) kcal/mol. These results show that electron correlation has a small effect on barriers of inversion (SiH^?₃) or pseudorotation (SiH^?₅), but may have a pronounced effect on reaction energies even if all systems involved have closed shells. The correlation energy contributions are analyzed in terms of intrapair and interpair terms in order to get a better understanding of the influence of correlation on reaction and activation energies.     

Effect of internal excitation on the collision-induced dissociation and reactivity of Co 2 +

The kinetic energy dependence of collision-induced dissociation (CID) of dicobalt ion (Co ₂ ⁺ ) with He, Ar, and Xe has been investigated using guided ion-beam mass spectrometry. The change in efficiency of CID as the target gas is changed is in general agreement with previous CID studies of other systems: the cross section with Ar is 0.5 that with Xe, and no product ions are found with He. By varying the conditions under which the reactant ions are formed, the degree of internal excitation of the dicobalt ions is changed. The internal energies can be characterized by a Maxwell-Boltzmann distribution. We find that CID and reactions with O₂ and CO are very sensitive to Co ₂ ⁺ internal energy. The bond-dissociation energy derived from this work is D^o(Co ₂ ⁺ )=2.75±0.10 eV (63.4±2.3 kcal/mol). The Co ₂ ⁺ results are compared with a previous study of Fe ₂ ⁺ .     

Relaxation behavior of selenium based glasses

Summary Relaxation behavior of Ge_ySe_100-y (y=8 and 10) glasses related to the viscosity behavior was studied by dilatometry. The method of two consecutive temperature jumps was applied to study the volume relaxation. The relaxation response can be described by Tool-Narayanaswamy-Moynihan model and the parameters of this model h*, , x, A were determined using curve fitting method and characteristic times method. Viscosities of studied materials in the range of 10⁸-10¹³ Pas were measured by penetration method. The calculated values of activation energies of viscous flow E are close to the values of effective activation energies of relaxation h* for studied chalcogenide materials.     

An ab initio Molecular Orbital Study of the Conformational Properties of all-( Z )-Cyclododeca-1,4,7,10-tetraene

 Ab initio HF/6-31G^* and MP2/6-31G^*//HF/6-31G^* methods were used to calculate the structure optimization and conformational interconversion pathways for all-(Z )-cyclododeca-1,4,7,10-tetraene. This compound adopts the symmetrical crown (C _4v) conformation. Ring inversion takes place via symmetrical intermediates, such as boat-chair (BC, C _s) and twist (C _2h) conformers and requires about 22.3 kJ · mol⁻¹. The calculated strain energies for BC and twist conformers are 5.9 and 13.5 kJ · mol⁻¹. The results of semiempirical AM1 calculations for structural parameters and relative energies of the important geometries of the title compound are in good agreement with the results of ab initio methods.     

The parameter dependence of calculated koopmans'defects in the framework of a model hamiltonian verified in the case of transition metal compounds

The validity of Koopmans' theorem in the lower energy region of trimethylenemethane iron tricarbonyl (1) is studied by means of a semi-empirical IN Reorganization energies are investigated as a function of the one-electron resonance integral β_μυ^AB and as a function of the one- and two interaction (γ_μυ^AA, K_μυ^AA and γ_μυ^AB). β_μυ^AB determines the kinetic energy of the interacting enlarged kinetic energy. The two-center electron repulsion intergral γ_μυ^AB have been calculated by means of an exponential formula with a short-range potentials with large γ_μυ^AB gradients pronounced reorganization energies are predicted while negligible defects even for stro case of smooth repulsion potentials with small γ_μυ^AB gradients. The largest parameter dependence of the calculated reorganization energie one-center electron—electron interaction integrals. With enlarged γ_μυ^AA and K_μυ^AA values enhanced Koopmans' defects are calculted in the framework of many body perturbation theory based on the Green's function formalism. A renormalized diagonal approximation for the self and correlation increments. The net defects are predominantly determined by electronic relaxation and modifications of the correlation energy in the ca of ground state pair-correlation (pair-removal) is only of minor importance.     

γ-Alumina-supported boron trifluoride: Catalysis, radiotracer studies and computations

The irreversible adsorption of boron trifluoride on calcined γ-alumina and amorphous chromia, in both cases at room temperature, has been studied using [¹⁸F]-labelled BF₃. Although the resulting γ-alumina surface has some catalytic activity for the room temperature fluorination by anhydrous HF of CH₃CCl₃ under static conditions, its activity is far lower than that of γ-alumina, which has been fluorinated with SF₄, nominally at room temperature. A possible explanation for the observed behaviour is given.     

A theoretical study of the condensation reactions of methyl cation with ammonia,water, hydrogen fluoride and hydrogen sulphide

Ab initio molecular orbital calculations have been used to study the condensation reactions of CH₃^? with NH₃, H₂O, HF and H₂S. Geometry optimization has been carried out at the Hartree—Fock (HF) level with the split-valence plus d-polarization 6-31G* basis set and improved relative energies obtained from calculations which employ the split-valence plus dp-polarization 6-31G** basis set with electron correlation incorporated via Moller—Plesset perturbation theory terminated at third order (MP3). Zero-point vibrational energies have also been determined and taken into account in deriving relative energies. The structures of the intermediates CH₃XH^? (X = NH₂, OH, F and SH) have been obtained and dissociation of these intermediates into CH₂X⁺ + H₂ on the one hand, and CH₃^? + HX on the other, has been examined. It is found that for those species for which the methyl condensation reaction is observed to have an appreciable rate (X = NH₂ and SH), the transition structure for hydrogen elimination from CH₃XH^? lies significantly lower in energy than the reactants CH₃^? + HX (by 75 and 70 kJ mol^?1 respectively). On the other hand, for those species for which the methyl condensation reaction is not observed (X = OH and F), the transition structure for H₂ elimination lies higher in energy than CH₃^? + HX (by 6 and 87 kJ mol^?1 respectively).     

Probing trapped ion energies via ion-molecule reaction kinetics: Quadrupole ion trap mass spectrometry

We present a detailed study of the energies of the ions stored in a quadrupole ion trap mass spectrometer (QITMS). Previous studies have shown that the rate constant, k, for the charge exchange reaction Ar⁺ N⁺ ₂ →, N⁺ ₂+Ar increases with increasing ion-molecule center-of-mass kinetic energy (K.E._cm). Thus, we have determined k for this chemical “thermometer” reaction at a variety of Ar and N₂ pressures and have assigned K.E._cm values as a function of the q₂ of the Ar⁺ ion both with and without He buffer gas present in the trap. The K.E._cm energies are found to lie within the range 0.11–0.34 eV over the variety of experimental conditions investigated. Quantitative “cooling” effects due to the presence of He buffer gas are reported, as are increases in K.E._cm due to an increase in the q₂ of the Ar⁺ ion. “Effective” temperatures of the Ar⁺ ions in He buffer are determined based on a Maxwell-Boltzmann distribution of ion energies. The resulting temperatures are found to lie within the range ≈ 1700–3300 K. We have also examined the K.E._cm, values arising from the chemical thermometer reaction of O⁺ ₂ with CH₄, as previous assignments of effective ion temperatures based on this reaction have been called into question.     

A Hirshfeld interpretation of the charge,spin distribution and polarity of the dipole moment of the open shell \left( {^{3} \Sigma^{ - } } \right) phosphorus halides: PF and PCl

Optimized geometries and energies, vertical excitation energies and vibrational frequencies are reported for nine cations MX₃ ⁺, with M = B, Al, Ga, and X = F, Cl, Br. Density functional theory using long-range corrected functionals, coupled cluster and multireference configuration interaction methods were applied with triple-zeta polarized basis sets. All cations were shown to be distorted from the high D_3h to the lower C_2v symmetry due to a strong pseudo Jahn–Teller effect. Geometry optimizations lead to two ²B₂ states, one with an X(axial)–M–X angle above 120°, to give a structure with one short and two long bonds (1S2L), the other having such angle below 120°, resulting in a structure with two short and one long bond (2S1L). In most cases, the 1S2L structure was found to be more stable than 2S1L, but the stabilization energies of 1S2L and 2S1L differ by no more than 0.2 eV. There is a saddle point at D_3h symmetry. Adiabatic and vertical ionization energies of MX₃ are also reported. Good to excellent agreement with available experimental data was found.     

线性BC2nB (n＝1～12)的结构特征和电子光谱的理论研究

应用密度泛函理论, 在B3LYP/6-31G^*水平上优化得到了线性簇合物BC_2nB (n＝1～12, D_(h)的平衡几何构型, 并计算了它们的谐振动频率. 在优化平衡几何构型下, 通过TD-B3LYP/cc-pvDZ和TD-B3LYP/cc-pvTZ计算, 分别得到了n＝1～12和n＝1～7的电子跃迁的垂直激发能和对应的振子强度. 在B3LYP/6-311＋G^*水平上计算得到了簇合物BC_2nB (n＝1～12, D_(h)的电离能. 基于计算结果, 导出了BC_2nB体系电子跃迁能以及第一电离能与体系大小n的解析表达式.     

AB initio calculations of the stability of the OH+4 and FH+3 ions

Some geometric configurations of the OH⁺₄ and FH⁺₃ ions have been calculated by the SCF MO LCAO method using linear combinations of gaussian lobe functions. The total electronic energies of the systems under study are lower than the sum of the energies for H₂O and H⁺₂ or OH⁺₃ and H, and HF and H⁺₂ or FH⁺₂ and H, respectively.