Predissociation lifetime of the 1σ g 2 2σ g diabatic state of He 2 + : a one-channel approach

Summary This work is concerned with the application of a one-channel model to obtaining predissociation lifetimes and transition rates in a system of crossing diabatic states. The calculation focuses on the first shape resonance of the 1 _g ² 2 _g diabatic state of He ₂ ⁺ , which is relatively stable with respect to tunneling. This resonance predissociates as a result of the 1 _g ² 2 _g state being crossed by the 1 _g 1 _u ² dissociative diabatic state near the resonance level. We have estimated its predissociation lifetime to be of the order of 10^–11 s.     

Diatomic interactions in momentum space. The 2pπ u and 3dπ g states of H 2 + system

The recently proposed method of momentum electron density for interatomic interactions is applied to the two states of the H ₂ ⁺ system. The processes of the attractive 2P _u and repulsive 3d _g interactions are analysed based on the behaviour of the momentum density and Compton profile. The results are compared with the previous ones for the 1 _{S g} and 2p _u states. The guiding principle of contraction and expansion for the energy-density relation in momentum space is shown to be common to both the and states.     

Calculation of σ→π* and π→σ* transitions in vinylboranes

Calculations are presented of the energies of the ground and excited and electronic states of ethylene and substituted vinylboranes. The Pople-Segal-Santry method was employed throughout. It is concluded that the excited state of lowest energy in ethylene has * character whilst the lowest energy ultra-violet spectral bands of the latter compounds stem from ^* transitions.

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Zusammenfassung Valenzelektronenrechnungen nach Pople-Segal-Santry wurden für Äthylen und Vinylborane durchgeführt. Danach hat der niedrigste angeregte Zustand von Äthylen ^*-Charakter, während die längstwellige UV-Bande der Vinylborane einem ^* -Übergang entspricht.

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Résumé Calculs de l'énergie pour les états fondamentaux et excités et de l'éthylène et des vinylboranes substitués. Utilisation de la méthode de Pople-Ségal-Santry. L'état excité le plus bas pour l'éthylène résulte d'une transition ^* , alors qu'il résulte d'une transition ^* pour les vinylboranes.

     

Calculation of two-center zero-field splitting integrals

Two-center zero-field splitting (ZFS) integrals have been calculated by numerical integration of Coulomb repulsion integrals which are evaluated over basic charge distributions as defined by Roothaan in terms of Slater atomic orbitals. The method is applied to the calculation of the ZFS integrals for -, - and - electron interactions on C, N and N⁺ centers. Numerical results are given.

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Zusammenfassung Zweizentren ZFS-Integrale sind mittels numerischer Integration von Coulombintegralen berechnet worden, und zwar die -, -- und --Integrale an C-, N- und N⁺-Zentren. Die numerischen Resultate werden mitgeteilt.

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Résumé Les intégrales bi-centriques de séparation à champ nul (ZFS) ont été calculées par intégration numérique des intégrales de répulsion coulombiennes évaluées pour les distributions de charge fondamentales définies par Roothan en termes d'orbitales atomiques de Slater. La méthode est appliquée au calcul des intégrales ZFS pour les interactions -, - et - sur les centres C, N et N⁺. Résultats numériques.

     

The electronic spectrum of acrylonitrile

The vapor absorption spectrum of acrylonitrile CH₂CHCN has been measured in the vacuum ultraviolet region. In addition, an all-valence-electron molecular orbital calculation has been used to calculate the electronic structure and spectrum of the molecule. On the basis of the MO calculation, as well as a vibrational analysis of the observed spectrum, several electronic transitions are assigned. The lowest energy absorption band (2107Å, = 150) is assigned as an n ^* transition. Absorption bands at 2030Å (=1600), 1725Å ( = 2100), and 1570Å ( = 1920) are assigned as 0–0 bands associated with transitions that are, respectively, ^*,^*, and ^* in character.

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Zusammenfassung Das UV-Absorptionsspektrum von dampfförmigen Acrylnitril wurde gemessen und eine CNDO/2-Rechnung für die Elektronenstruktur durchgeführt. Auf dieser Basis konnten unter Zuhilfenahme der Analyse der Schwingungsstruktur im beobachteten Spektrum mehrere Banden zugeordnet werden: die 2107-Å-Bande ( = 150) einem n^*-Übergang, die drei Banden bei 2030Å ( = 1600), 1725Å ( = 2100) und 1570 Å ( = 1920)0-0-Übergängen von ^*-, ^*- bzw. ^*-Banden.

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Résumé Mesure du spectre d'absorption en phase vapeur de l'acrilonitrile CH₂CHCN dans la région de l'ultraviolet. Par ailleurs, la structure électronique et le spectre de la molécule ont été calculés à l'aide d'une méthode des orbitales moléculaires semi-empirique pour tous les électrons de valence. Sur cette base, ainsi que sur une analyse vibrationnelle du spectre expérimental, on procède à l'attribution de plusieurs transitions électroniques. La bande d'absorption de plus basse énergie (2107 Å, = 150) est attribuée à une transition n ^*. Les bandes d'absorption à 2030Å ( = 1600), 1275Å ( = 2100) et 1570Å ( = 1920) sont considérées comme des bandes 0 - 0 associées à des transitions ^*, ^* et ^* respectivement.

     

Binding/antibinding analyses for diatomic interactions H 2 + system

The region-functional concept of electron density has been quantitatively examined for 1s_g, 2p_u, 2p_u, and 3d_g states of H ₂ ⁺ system on the basis of Berlin diagram which divides the three-dimensional molecular space into binding and antibinding regions. The electronic charge, Hellmann-Feynman (H-F) force, and stabilization energy of the system are partitioned into the binding and antibinding contributions by the regional integrations.Dynamic behaviors of the electron density (i.e. electron-cloud preceding and following) during the interaction processes are also clarified using the centers of electron density and force density.Differences in attractive and repulsive, and - and -type interactions are discussed from the force and density point of view.     

New notions of active surface composition of reforming catalysts

Some peculiarities of adsorption and catalytic properties of electron deficient platinum atoms (Pt) in reforming catalysts are presented. It appears possible to improve catalysts modifying Pt centers with -donor molecules.     

Quantum-chemical study of allylic compounds with two bonded heavy atoms

It has been shown by the CNDO method that the bathochromic shift of the long-wave absorption band in the transition from allylstannane to compounds of the type C=C-C-Sn-X and C=C-Sn-X (where X is a heavy atom) is connected with the formation of a low-energy vacant *_S-X orbital, localized mainly in the region of the Sn-X chemical bond, and of an occupied _Sn-X orbital, the energy of which is somewhat higher than of the _C-Sn orbital. The dependence of the position of the long-wave absorbance region on conformation is related to the fact that, in planar and nonplanar conformers, the long-wave transitions are of a different type ( * and *, respectively); the bathochromic shift is determined to a large degree by the difference in the energies of the highest occupied MO ( - ) in the s-trans form. In the nonplanar conformers the heavy atom orbitals interact with the -orbital of the ethylene moiety through the bridge group; this leads to a significant delocalization of the HOMO and to a considerable change in its energy. On the other hand, their interaction with the *-orbital in compounds of the C=C-C-Sn-X type is very low and does not favor the delocalization of lower vacant MO. In vinyldistannane the *-orbital is noticeably delocalized, due to the interaction with the *_Sn-Sn orbital in planar and with the *_Sn-Sn orbital in nonplanar conformers.N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, 117913 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 3, pp. 636–641, March, 1992.     

An extension of the CNDO/2 formalism for the study of transition metal complexes

A previously described extended CNDO/2 method is used for investigating the energy level distribution and electronic structure of trifluorophosphine metal complexes: Cr(PF₃)₆, Fe(PF₃)₅, Ni(PF₃)₄. The results are compared with the few experimental data which are known for these complexes. The metal-phosphorus bonds show large (P M) and (M P) charge transfers but small total charge transfers (M P) which induce on the metal in any case a small positive charge.Such ( + ) coordination bonds seem to be generally characterized by small bond overlap populations (or small Wiberg indices).     

Detector quantum efficiency: An important parameter for FT-IR spectroscopy

Spectral detectivities (D ^*()) are commonly used to characterize the sensitivity of infrared detectors, but for most spectroscopic purposes they are very misleading.For photon detectorsspectral detector quantum efficiencies ( _q ()) are needed in order to calculate the (S/N) ratio for the photon-noise limited situation. An equation to calculate _q(#x03C3;) fromD ^*() values is presented. The results for some common IR-detectors are surprising.As an application for the use of _q () values theS/N ratio of an FT-IR spectrum from an optimized FTS instrument under photon-limited conditions is given.     

Generalized quantum mechanical two-centre problems. IV. On the accuracy of simple LCAO approximations for H 2 + states and the Eckart criterion

If x denotes an exact solution of the quantum mechanical two centre Coulomb problem, we optimize a normalized LCAO approximation by making the overlap S = (x¦) a maximum. In this context we study how a weight factor (r _a r _b )^–1 in the definition of the inner product changes the approximation and the expectation value of electronic energy. Finally we compare the lower bound given by the Eckart criterion with the exact overlap. Results are reported for H ₂ ⁺ states 1s_g and 2p_u.Dedicated to Professor Hermann Hartmann on occasion of his 70th birthday on May 4th, 1984     

New method for the synthesis of σ-β-ketovinyl derivatives of cyclopentadienyliron dicarbonyl

Conclusions A new method was developed for the synthesis of -RCOCH=CHFe(CO)₂C₅H₅- by the reaction of-iodovinyl ketones with [Fe(CO)₂C₅H₅-]₂. In this case it was demonstrated for the first time that the reaction of organic haloderivatives with [Fe(CO)₂C₅H₅-]₂ can be used for the synthesis of -RFe(CO)₂C₅H₅-.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1646–1647, July, 1972.     

Quantum chemical study of allyl halides

Using the MNDO method we have shown that the bathochromic shift of the longwavelength region of absorption in the electronic spectrum of allyl bromide and allyl iodide on going to nonplanar conformers is due to the fact that, in this case, the transition ^* to the low-lying ^* orbital appears, which is forbidden in planar forms. In allyl fluoride and allyl chloride, , and the transition ^*, which depends little on conformation, is long-wavelength. In the gauche conformers of allyl halides, the frontier MOs are appreciably delocalized as a result of - interaction; in the s-trans conformer, the unshared pair of the heteroatom makes an insignificant contribution to the orbital only in allyl iodide.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2552–2557, November, 1989.     

Electronic effects of 1-(1, 7-B6H6C2H) and 1-(1,6-B7H7C2H) groups

Conclusions 1-[1,7-Dicarbaclozooctaboran(8)yl] (induction constant _i=0.08 and resonance constant _R°=–0.02) and 1-[1,6-dicarbaclozononaboran(9)yl] (=0.09 and _R°=0.05) groups are weak electron-acceptor groupings.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 574–576, March, 1972.     

Infrared spectra and theoretical study ofE-3-(2-R-vinyl)-2-benzothiazolinones

The C=O stretching frequencies ofE-3-(2-R-vinyl)-2-benzothiazolinones (1 a–1 p) were measured in CCl₄ and CHCl₃ and correlated with ⁺ and * substituent constants. Thev(C=O) vs * (R) correlation was compared to an analogical relationship obtained with 3-R-2-benzothiazolinones (2). The electronic structure and geometry of compounds was investigated by CNDO/2 and PCILO methods. The results of both the spectral and theoretical studies showed forE-3-(2-R-vinyl)-2-benzothiazolinones a preference of the N—C-s-cis conformation (3), in which the substituent effects are transmitted to the C=O group very efficiently. The transmission factor for the CH=CH group was determined according to the definition ofJaffé. The role of inductive effects, delocalization of the nitrogen lone-pair electrons as well as the through-space interaction between the C=O and C=C bonds is discussed in terms of transmission mechanism and structural properties.

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Infrarotspektren und theoretische Untersuchungen vonE-3-(2-R-vinyl)-2-benzo-thiazolinonen

Zusammenfassung Es wurden die C=O-Streckfrequenzen vonE-3-(2-R-vinyl)-2-benzothiazolinonen (1 a–1 p) in CCl₄ und CHCl₃ gemessen und mit -, ⁺- und *-Substitutionskonstanten korreliert. Diev(C=O)-*-Korrelation wurde mit einer analogen Beziehung für 3-R-Benzothiazolinonen (2) verglichen. Die elektronische Struktur und die Geometrie der Verbindungen wurden mittels CNDO/2- und PCILO-Berechnungen untersucht. Es ergab sich dabei sowohl aus den spektros-kopischen als auch aus den theoretischen Ergebnissen eine N—C-s-cis-Konformation (3) für dieE-3-(2-R-vinyl)-2-benzothiazolinone, da dies eine günstige Geometrie zur Übermittlung von Substitutionseffekten zur C=O-Gruppe ergibt. Der Transmissionsfaktor für die CH=CH-Gruppe wurde nach der Definition vonJaffé bestimmt. Die Rolle von induktiven Effekten, der Delokalisierung des freien Elektronenpaares am Stickstoff und der C=O....C=C-Wechselwirkungen durch den Raum wurde auf Basis von Transmissionsmechanismen und strukturellen Eigenschaften diskutiert.

     

Ionization potentials of halides. Substituent effects in Cl-, Br-, and I-centered radical cations

The first vertical ionization potentials (I) of halides HalX (Hal = Cl, Br, I; X is an inorganic or organic substituent) are linearly related to the inductive (_I), resonance (_R ⁺), and polarizability () constants of the substituents X (I = a + b_I + c_R ⁺ + d). As the atomic number of the Hal element in the Hal^·+X radical cations increases, the inductive interaction is strengthened while the polarizability interaction is weakened. Conjugation remains virtually independent of the Hal atom. The resonance _R ⁺-constants of the MX₃ (M = Si, Ge, Sn, Pb) substituents bound to the Hal^·+ radical cation centers were first calculated.     

Kinetic characteristics of the ring-chain tautomeric equilibria of 2,3,3-trimethyl-1-aryl-2-hydroxy-5-pyrrolidones

The kinetics of the ring—chain tautomeric equilibria of a number of p-substituted 2,3,3-trimethyl-1-aryl-2-hydroxy-5-pyrrolidones in 50% aqueous pyridine were studied by dynamic PMR spectroscopy, and the effect of substituents on the kinetic parameters of this process was determined. The free energies of activation (G) decrease regularly on passing from electron-donor to electron-acceptor substituents. A good correlation between G and the ⁺ and substituent constants is observed. On the basis of the data obtained, it was concluded that the ratedetermining step in the process is detachment of a proton under the influence of the base to give the corresponding anion.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 758–763, June, 1978.     

Intensity of the η(C≡C) Bands in the IR Spectra of Acetylene Derivatives and σR 0 Constants of Organosilicon,Organogermanium, and Organotin Substituents

The integral absorptivities of shape-characteristic (CC) bands in the IR spectra of 66 acetylene derivatives RCCX (R = H, Me₃M; X are inorganic and organic substituents) are related by a common linear equation to the _R ⁰ constants of the R and X substituents. The _R R⁰ constants of 10 Alk₃M substituents were calculated. The _R ⁰, _R , and _R ⁺ constants of Me₃M substituents were analyzed. The positive _R ⁰ values (0.12, 0.06, and 0.04 for R = Si, Ge, and Sn, respectively) suggest that in the ground electronic state of Me₃MCCX molecules the resonance acceptor effect of the Me₃M substituents (d, conjugation) prevails over donor (, conjugation). The first effect attenuates and the second enhances as the atomic number of M increases.     

Absorption spectra and bond type in Co(II) aquoamino complexes

Absorption spectra are reported for solutions containing Co(II) and ammonia. Spectra are calculated for five Co(II) aquoamino complexes. The spectra are used to determine Dq and B, parameters of the bonds in these compounds. It is found that Dq and B change nonlinearly and nonadditively. The parameters _c, Dt, Ds, and have also been established for [Co(H₂O)₆]²⁺ and [Co(NH₃)₆]²⁺. The parameter variation can be explained if the H₂O molecules form weaker bonds to the central atom than do the NH₃ molecules, but are capable of d-p interaction.     

Determination of the ratio of the hydrogen and manganese absorption cross sections by the manganese bath technique

The ratio of the hydrogen and manganese neutron absorption cross sections, _H/_Mn, is a most important parameter in the determination of radioactive neutron source strength by the manganese bath technique. The ratio is well measured by observing the change in⁵⁶Mn activity induced in the manganese bath by a fixed neutron source as the manganese concentration of the bath is changed. In the present study, the neutron source was a Maxwellian beam from²⁵²Cf. Concentrations were determined by the two methods: volumetric and gravimetric. The cross section ratio has turned out to be _H/_Mn=0.02506.