SCF MO LCGO studies on the hydration of ions: The system Li+·2H2O

The energy of the dihydrated lithium cation Li⁺·2H₂O is studied in several different points within the SCF MO LCAO framework, using a gaussian basis set to approximate the wavefunction. The computed binding energies (hydration energies) and bond distances are compared to the values found for the monohydrate. The results are discussed in view of ion-solvent interaction, and especially of the effect of ions on adjacent hydrogen bonds, in aqueous solutions.It is a pleasure to thank our technical staff for the careful preparation of the input for the programs and for its enthusiastic and skilful assistance in running the computer.     

SCF LCAO MO studies on the hydration of ions: The system F− · 2H2O

The energy surface of the dihydrated fluoride anion (F·2H₂O)^–1 is studied for a number of different geometry points near the equilibrium structure within the SCF LCAO MO framework, using an extended gaussian basis set to approximate the molecular wavefunctions. For the first and second hydration step of the fluoride anion the corresponding hydration energies are calculated to beB ₁ ^scf =24.1 kcal/mole andB ₂ ^SCF =20.8 kcal/mole (experimental measurements: 23.3 kcal/mole and 16.6 kcal/mole, respectively). The hydration energies and equilibrium bond distances obtained for the dihydrated fluoride anion (F·2H₂O)^– are compared with those found for the monohydrate (FHOH)^– and with corresponding results of the dihydrated lithium cation (Li · 2H₂O)⁺. The system (F·2H₂O)^– is taken as a very simple model to discuss some basic features of the hydration process of small ions and to study the influence of a negative ion on an adjacent hydrogen bond.We would like to thank our technical staff for valuable help in carrying out these calculations.     

SCF MO LCGO Studies on hydrogen bonding: The system NH3 · H2O

The energy hypersurface of the system NH₃ · H₂O is investigated for a number of different internuclear geometries. In the minimum energy structure involving a linear hydrogen bond, NH₃ acts as proton acceptor. The binding energy of the system is calculated to be 6.28 kcal/mole and the bond distance d(NO) to be 3.07 Å. The potential energy curve of the inversion of the hydrogenbonded NH₃ is computed and discussed.

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Zusammenfassung Die Energiehyperflächen des NH₃ · H₂O-Systems wurden für eine Anzahl von verschiedenen geometrischen Anordnungen untersucht. Im Falle der Struktur minimaler Energie wird eine lineare Wasserstoffbindung gebildet, NH₃ wirkt als Protonakzeptor. Die Berechnungen ergeben eine Bindungsenergie des Systems von 6,28 kcal/Mol und einen NO-Abstand von 3,07 Å. Außerdem wurde die Potentialkurve für die Inversion des über eine Wasserstoffbrücke gebundenen NH₃ berechnet und diskutiert.

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It is a pleasure to thank our technical staff for the careful preparation of the input for the programs and for its skillful assistance in running the computer.     

SCF MO LCGO studies on hydrogen bonding: The system (HOHOH)−

The closed shell ground state of the system (HOHOH)^– has been studied for different geometrical configurations within the SCF LCGO MO framework, using an extended basis set of gaussian type functions to approximate the molecular wavefunctions. The most stable structure was found to have a linear, slightly asymmetrical hydrogen bridge between the two oxygen nuclei. The OO-distance was determined to be d(OO)=4.75 a.u. (=2.51 Å), and a binding energy, relative to the subsystems H₂O and OH^–, of B=24.3 kcal/mole was obtained, in reasonable agreement with the most recent experimental measurement (B _exp = 22.5 kcal/mole). The proton transfer process between the two subsystems has been studied in a range near the equilibrium OO-distance.     

SCF LCGO MO studies on the fluoronium ion FH 2 + and its hydrogen bonding interaction with hydrogen fluoride FH

The stability and geometrical structure of the fluoronium ion is investigated using the onedeterminant SCF LCAO MO method. The equilibrium geometry is characterized by a bond length of d(FH)=0.95 Å and a bond angle of 114.75°. The proton binding energy is determined to be 120.1 kcal/mole. The molecules FH ₃ ²⁺ and FH₃ are found to be unstable. A binding energy of 30.7 kcal/mole is obtained for the hydrogen bond formation between the systems FH ₂ ⁺ and FH. In the minimum energy structure the central proton is situated midway between the two F atoms in a symmetrical single minimum potential. The general behavior of the potential curves of the di-solvated proton involving NH₃, OH₂, and FH as solvent molecules is discussed. In all these cases double minimum potentials are found, if the equilibrium separation between the heavy atoms is larger than approximately 2.4 Å, and single minimum potential for separations smaller than this value.     

Ab initio SCF MO study of hydrogen bonds between H2S and H2O molecules

The hydrogen bonds between H₂S and H₂O molecules are calculated through anab initio, LCAO MO SCF method using a Gaussian type orbital double-zeta basis set. The capacity of the H₂S molecule to act as an electron acceptor is confirmed. Consultant of the Instituto Mexicano del Petróleo.     

Structural and electronic properties of complexes between Li+, Na+, Be2+, and Mg2+ ions and HF,H2O,and NH3 molecules

Theoretical and Experimental Chemistry -     

SCF calculations for H 2 + , Li 2 + and LiH+ with atomic basis sets enlarged by bond functions

To simulate the charge distortion in the formation of a molecule from the separated atoms, a set of concentrics-type Gaussian functions is placed on the internuclear axis in addition to thes-type atomic basis functions to construct the molecular orbital for the one valence-electron systems H ₂ ⁺ , Li ₂ ⁺ and LiH⁺. This simple model gives 90.1%, 75.2% and 61.7%, respectively, of the improvement over minimal basis relative to Hartree-Fock energies.Supported in part by a research grant to Rice University from the Robert A. Welch Foundation.     

Non-empirical SCF MO studies on the protonation of biopolymer constituents

Side-chain proton affinities for a series of peptide-forming amino acids have been calculated using ab initio Hartree-Fock-Roothaan SCF method; the order of proton affinities is Arg > His > Ser Tyr Lys. Protonation of some side-chains in a protein may introduce new energy levels in the band gaps thus fundamentally altering the conduction properties of the proteins.This paper is dedicated to Professor H. Hartmann for his 65th birthday.Guest at the Laboratory of the National Foundation for Cancer Research at the Chair of Theoretical Chemistry, University of Erlangen-Nürnberg.     

Non-empirical SCF MO studies on the protonation of biopolymer constituents

Proton affinities of a large number of tautomeric adenine and guanine structures have been calculated using theab initio Hartree-Fock-Roothaan SCF method. For guanine, and to a lesser extent for adenine, it is likely that several protonated forms may co-exist in acidic solutions. Protonation at the free adenine and guanine positions in DNA may introduce effective acceptor levels between the energy bands of the polymer that may cause fundamental changes in the conduction properties of DNA.     

Non-empirical SCF MO studies on the protonation of biopolymer constituents

Proton affinities of several of the tautomeric forms of cytosine and thymine have been calculated using theab initio Hartree-Fock-Roothaan SCF method. Several of the most stable protonated forms may be obtained by direct protonation from one of the two most stable neutral forms. The calculated total energies do not exclude the possibility of the coexistence of several protonated forms in acidic solutions.     

Perturbed SCF MO calculations. Electrical polarizability and magnetic susceptibility of HF,H2O,NH3 and CH4

The perturbation theory is used to evaluate first order SCF corrections upon Roothaan type molecular wave functions due to one-electron perturbations. The method is applied to the one-center SCF MO wave functions of HF, H₂O, NH₃ and CH₄ to calculate the electrical polarizability and the magnetic susceptibility tensors. The results obtained agree reasonably well with the available experimental data. The effects of the limited number of basis functions upon the final results are discussed.

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Zusammenfassung Es werden Störungen erster Ordnung an SCF-MO-Wellenfunktionen, hervorgerufen durch Einelektronenstöroperatoren, im Rahmen der Störungstheorie behandelt. Insbesondere werden die Tensoren der elektrischen Polarisierbarkeit und der magnetischen Suszeptibilität unter Verwendung von Einzentrumfunktionen für HF, H₂O, NH₃ und CH₄ berechnet. Die Ergebnisse werden mit den verfügbaren experimentellen Daten verglichen. Die Effekte der endlichen Basisgröße auf die Resultate werden diskutiert.

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Résumé La théorie des perturbations est utilisée pour évaleur les corrections SCF du premier ordre, aux fonctions d'onde moléculaires du type Roothaan, dûes à des perturbations monoélectroniques. La méthode est appliquée aux fonctions d'ondes SCF MO à un centre de HF, H₂O, NH₃ et CH₃, pour le calcul des tenseurs de polarisabilité électronique et de susceptibilité magnétique. Les résultats obtenus sont en accord raisonnable avec les données expérimentales disponibles. L'effet du nombre limité de fonctions de base sur le résultat est discuté.

     

Collisional studies of some C3H7O+ ions

Journal of The American Society for Mass Spectrometry - The C3H7O+ ions of nominal structures 1, 2, 3, and 4, produced by protonation of acetone, propanal, propylene oxide, and oxetan,...     

The variable core approach in the SCF MO calculation of heteroatomic systems

A charge density dependency of the core energy in the SCF MO theory has been derived. According to the present theory, the core energy, U , associated with the ^th 2p-AO should linearly vary with the charge density, q . SCF MO calculations based on this variable core approach have been carried out for some N-heterocycles, aromatic amino derivatives, and protonated pyridine. The results for the electronic spectra of neutral molecules are almost the same as those based on the conventional SCF MO method. However, the calculated charge distributions are somewhat different. An interesting result is that the present theory calculates a slightly negative net charge at the meta positions in aniline.

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Zusammenfassung Es wird eine SCF-MO-Methode entwickelt, in der das dem 2p -AO entsprechende Rumpfintegral U linear von der Ladungszahl q abhängt. Es werden einige N-Heterocyclen, aromatische Aminoderivate und das Pyridinium-Ion durchgerechnet. Die Elektronenspektren der neutralen Moleküle ergeben sich wie mit der üblichen Methode; die Ladungsverteilung ist jedoch etwas verändert. Beispielsweise führt die neue Methode zu einer geringen negativen Überschußladung in der Metaposition des Anilins.

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Résumé On a établi une relation de dépendance entre l'énergie de coeur et la densité de charge en méthode SCF MO. Salon la théorie ci-dessous l'énergie de coeur U , associée à la ième orbitale atomique 2, devrait varier linéairement avec la densité de charge q . Des calculs SCF MO basés sur cette hypothèse de coeur variable ont été effectués pour quelques N-hétérocycles, dérivés aminés aromatiques et pour la pyridine protonisée. Les résultats concernant les spectres électroniques des molécules neutres sont pratiquement identiques à ceux obtenus par la méthode SCF MO conventionelle. Cependant les distributions de charges obtenues sont quelque peu différentes. Un résultat intéressant de cette théorie est la faible charge nette négative en position méta dans l'aniline.

     

Infrared spectra of Li2SeO4.H2O,Li2SO4.H2O and Li2(S,Se)O4.H2O

On of the hydrogen bonds formed by water molecules in lithium selenate monohydrate is evidently stronger than in the corresponding sulfate, whereas the other one is weaker. The temperature dependence of the stretching and bending modes of water is similar in both compounds, their frequencies decreasing on lowering the temperature. The study of mixed sulfate—selenate compounds made it possible to clearly show that the effective symmetry of the tetrahedral ions is higher than their local crystallographic one.