On interference of orbital communications in molecular systems

The atomic orbitals (AO) contributed by bonded atoms of molecular systems emit or receive the “signals” of electronic allocations to these basis functions, thus acting as the signal source (input) or receiver (output), respectively, in the associated communication network. Each orbital simultaneously participates in both the through-space and through-bridge probability propagations: the former involve direct communications between two AO while the latter are realized indirectly via orbital intermediates. This work examines the interference effects of the amplitudes of molecular probability scatterings, and introduces the operator representation of AO communications. The eigenvalue problem of the associated Hermitian operator combining the forward and reverse information propagations defines the stationary modes (“standing” waves) of the molecular propagation of electronic conditional probabilities. The combined effect of interference between the multiple (direct and indirect) information scatterings, which establishes the stationary distribution of electronic probabilities, is probed. The wave-superposition principle for the conditional-probability amplitudes of the generalized through-bridge information propagation is linked to the idempotency relations of the system density matrix. It explicitly demonstrates that the resultant effect of the probability propagations involving bridges containing all basis functions, at arbitrary bridge orders indeed generates the (stationary) molecular distribution of conditional probabilities.     

The asilomar conference on ion spectroscopy,October 16–20, 2009

The ASMS conference on ion spectroscopy brought together at Asilomar on October 16–20, 2009 a large group of mass spectrometrists working in the area of ion spectroscopy. In this introduction to the field, we provide a brief history, its current state, and where it is going. Ion spectroscopy of intermediate size molecules began with photoelectron spectroscopy in the 1960s, while electronic spectroscopy of ions using the photodissociation “action spectroscopic” mode became active in the next decade. These approaches remained for many years the main source of information about ionization energies, electronic states, and electronic transitions of ions. In recent years, high-resolution laser techniques coupled with pulsed field ionization and sample cooling in molecular beams have provided high precision ionization energies and vibrational frequencies of small to intermediate sized molecules, including a number of radicals. More recently, optical parametric oscillator (OPO) IR lasers and free electron lasers have been developed and employed to record the IR spectra of molecular ions in either molecular beams or ion traps. These results, in combination with theoretical ab initio molecular orbital (MO) methods, are providing unprecedented structural and energetic information about gas-phase ions.     

Stereochemical analysis by simplex representation of molecules

Stereoanalysis of molecules by partitioning a spatial structure into a system of simplices is described in detail. Potentialities of simplex representation of molecules in defining stereochemistry are demonstrated for chiral structures of various complexity and planar unsaturated molecules (“two-dimensional stereochemistry”). A concept of “stereochemical charge” is introduced. A. V. Bogatskii Physicochemical Institute, Ukrainian Academy of Sciences. Odessa State University. Translated fromZhurnal Strukturnoi Khimii, Vol. 39, No. 3, pp. 553–558, May–June, 1998.     

A method for population and bonding analyses in calculations with extended basis sets

Summary A method for population and bonding analyses in the calculations with extended basis sets is proposed. The definition and evaluation method of the atomic orbitals in molecular environments (AOIMs) are described. It is shown that the AOIMs can be divided into two subsets, the strongly occupied minimal compact subset {AOIM}_B and the very weakly occupied “Rydberg” subset {AOIM}_R, according to the orbital population obtained from Mulliken analysis with AOIMs as basis sets. The viewpoint of “molecular orbitals consisting of minimal atomic orbital sets” can be optimally realized in terms of {AOIM}_B. The Mulliken population based on AOIMs is reasonable and fairly stable to changes of basis sets. The Mayer bond orders calculated based on {AOIM}_B are quite stable to the changes of basis sets; therefore they can be used to measure objectively the contribution of individual atomic orbitals to bonding.     

Reinforcement by carbon black considered as a rate process

Summary Following a survey of the behaviour of elastomers loaded with carbon black, a mechanism of reinforcement is proposed which is based upon theDannenberg's concept of “mobile absorption” or “molecular slippage” of elastomer macromolecules on the carbon black surface, and treats their motion as a rate process. The behaviour of single molecular chains is described in detail.

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Zusammenfassung Aus einer kritischen Betrachtung des Verhaltens ru?gefüllter Elastomerer wurde ein Mechanismus für die Verst?rkung vorgeschlagen, demDannenberg's Konzept der „mobilen Adsorption“ oder „molekularen Gleitung“ der Elastomer-Makromoleküle auf der Ru?oberfl?che zugrundeliegt. Ihre Bewegung wurde kinetisch behandelt. Das Verhalten einzelner Molekülketten wird im Detail beschrieben.

     

Influence of the out-of-plane distortions of nuclear configurations of molecules with then-AO of the heteroatom directed along theC 2 symmetry axis on spin-orbit coupling between thenπ*- and ππ*-states

This paper studies changes in the matrix elements (U_mp) of spin-orbit coupling between the nπ^*- and ππ^*-states, which are induced by the (“chair,” “bath”) distortions of the nuclear configurations of molecules. The analysis is performed for acridine molecules in which the n-p_z atomic orbital (AO) of the heteroatom is directed along the C₂ symmetry axis. Earlier, for molecules with a planar nuclear configuration of C_2v symmetry and with the heteroatom lying on the C₂ axis, we established the dependence of U_mp on the symmetry of ππ^*-states [Γ(ππ^*)=A₁ or B₂]. The values of U_mp differ by more than one order of magnitude; this is in line with the difference between the interconversion rate constants (K_isc; two or three orders). In this work we have found that this contrast in U_mp (and, accordingly, in K_isc) is retained when the nuclear configuration of the acridine molecule is distorted to the “chair” (AC-A) configuration, although the individuality of both molecular orbital types (nσ-MO and π-MO) and states nπ^* and ππ^* is annihilated to a certain extent. For the “bath” (AC-B) conformation the difference in U_mp considerably diminishes. Reasons for the changes in the matrix elements of spin-orbit coupling and rate constants of the S-T conversion are analyzed. The available energy level diagram is critically analyzed, and a slightly different diagam as well as a scheme of nonradiating deactivation of acridine are suggested. L. Ya. Karpov Physicochemical Scientific Research Institute. Translated fromZhurnal Strukturnoi Khimii, Vol. 36, No. 2, pp. 292–297, March–April, 1995. Translated by L. Smolina     

Calculations of the geometries, electronic structures and nonlinear second-order optical susceptibilities of spiroannelated quinone-type methanofullerenes

 The equilibrium geometries, electronic structures and UV–vis spectra of a series of spiroannelated quinone-type methanofullerenes have been determined by using Zerner's intermediate neglect of differential overlap method. The results show that between fullerene and the addend there exists a special interaction, “periconjugation”, which results in through-space orbital interactions. The calculated UV–vis spectra are in good agreement with experiments. On the basis of the electronic spectra, the β values are calculated. The results show that spiroannelated quinone-type methanofullerenes have quite large β values. We attribute the large β values to both the charge transfer from C₆₀ to benzoquinone and on the C₆₀ three-dimensional conjugated sphere. Received: 17 December 2000 / Accepted: 16 March 2001 / Published online: 13 June 2001     

Time-dependent density functional theory study on electronic and spectroscopic properties for Ph<Subscript>2</Subscript>Bq and its complexes

The molecular structures of the ground state and the first singlet excited state for diphenylboron analogs of Alq₃ [Ph₂Bq where q is 8-hydroxyquinoline (QH)] and its three derivatives were optimized with the Density Functional Theory and ab initio “configuration interaction with single excitations” method, respectively. The frontier molecular orbital characteristics of Ph₂Bq were analyzed systematically in order to study the electronic transition mechanism. Electronic and spectroscopic properties of complexes have been investigated with Time-Dependent Density Functional Theory, which indicates that the emissions of Ph₂Bq and its derivatives originate from the electronic π → π* transitions within the QH ligands. That means that one might tune the emission wavelengths and improve charge transfer properties through the effect of substituent on the 8-hydroxyquinoline ligand. Similar calculations were carried out for isolated QH and its three derivatives for comparison. We found that the highest occupied molecular orbital and the lowest unoccupied molecular orbital of Ph₂Bq are similar to those of QH and their spectroscopic properties change similarly when they are substituted by the same group, which suggests that one can search possibility of a red or blue emission from Ph₂Bq derivatives by analyzing QH and its derivatives.     

Linearly polarized white fluorescence from shish-kebab type liquid crystalline poly(P-phenylenevinvlene)s with (P-phenylene)s as kebab

Liquid crystalline(LC) polymers with a shish-kebab-type moiety on their cross-conjugated(p-phenylene)s-poly(p-phenylenevinylene) s main chains were synthesized through Gilch polymerization in order to develop a kind of polymers available for linearly polarized white-light-emitting from single chain.In this system,the 2,5-bis(4’-alkoxyphenyl)benzene as the "kebabs" connects with poly(p-phenylenevinylene)(PPV) main chain backbone using its molecular gravity center and the PPV as the "shish" or "skewer"(the "shish-kebab").The polymers possess desirable properties such as excellent solubility and liquid crystalline properties.To drop the "kebabs" of the 2,5-bis(4’-alkoxyphenyl)benzene into the orientation microgroove of aligned polyimide film,not only the "shish" of polymer main chain can be aligned by the virtue of orientation of "kebabs" but also the uniform cross-conjugated structure between the "kebabs" and "shish" can be broken. Then,the alignment of the polymer main chain showed yellow light emission and was also accompanied by orientation of the LC side chains showing blue light emission,this gave rise to a notable linearly polarized white fluorescence.     

Critical points on vapor-liquid stratification curves in inhomogeneous systems

A historical information about the introduction of one of the main concepts in the theory of condensed phases, critical point, is given. The initial term, “absolute boiling temperature,” introduced by D.I. Mendeleev was formulated on the basis of deeper views on the nature of critical phenomena than later studies by T. Andrews, who suggested the term “critical temperature,” which became well established with time. Most interesting estimation of the studies by Andrews was given by D.I. Mendeleev. The concept of critical temperature and the investigations of D.I. Mendeleev were discussed.     

Use of unsymmetrical one-range addition theorems of Slater type orbitals in molecular electronic structure determination

In this work, the applicability of the unsymmetrical one-range addition theorems obtained from the use of complete orthonormal sets of Ψ^α-exponential type orbitals (Ψ^α-ETOs, where α = 1, 0, − 1, − 2, ...) to the study of electronic structure of molecules is demonstrated using minimal basis sets of Slater type orbitals (STOs). As an example of application of unsymmetrical one-range addition expansion method to evaluate the multicenter electronic integrals, the calculation has been performed for the ground state of BH ₃ molecule. The results of computer calculations for the orbital and total energies, and linear combination coefficients of symmetrized molecular orbitals are presented.     

Computational Study of Supramolecular Bis-porphyrin “Molecular Tweezers”

A computational study of a series of space separated bis-porphyrin “molecular tweezers” using semiempirical (AM1) and DFT (B3LYP and PBE1PBE) methods has been carried out. It was found that polynorbornane bis-porphyrin systems are significantly less rigid than previously thought. The variation of the metal–metal separation distance between the two porphyrin centers does not cause a significant energy change thus enabling these molecules to easily adjust to the optimal coordination distance required for complexation by various bidentate 4-pyridyl ligands inside the cavity of these “tweezers”. Article 54, ECCC-10, April 1-30 2005, http://www.eccc.monmouth.edu     

Tempered orbital energies in SCF MO calculations and their relation to the ordinate in Mulliken-Walsh correlation diagrams and extended Hückel orbital energies

An “average state” of a molecule is defined by distributing the electrons equally among the valence orbitals of a minimal basis set Hartree-Fock calculation. The resulting eigenvalues, called tempered orbital energies, behave much more like the Mulliken-Walsh diagram energies or extended Hückel eigenvalues than do the Hartree-Fock canonical orbital energies.     

The Si-doped planar tetracoordinate carbon (ptC) unit CAl<Subscript>3</Subscript>Si<Superscript>−</Superscript> could be used as a building block or inorganic ligand during cluster-assembly

Currently, the molecular assembly and growth from a small building block to the bulk compounds have become a focus in various fields. Ever being chemical curiosities, the “anti-van’t Hoff/Le Bel” realm that is associated with tetracoordinate or hypercoordiate planar centers has made vast progress. Being important in the fundamental research areas, the ptC species have potential applications in materials science. The existence of ptC in a divanadium complex and a large number of organometallic compounds have since been reported to possess ptC and these provide us with great hope that many more compounds with ptC building blocks may be synthesized in future. Herein, we report the assembly and stabilization of CAl₃Si⁻ in both the “homo-decked sandwich” and “hetero-decked sandwich” schemes at the B3LYP/6-311+G(d) level. We show that while the Si-doped indeed introduces much complexity during assembly, the electronic and structural integrity feature of CAl₃Si⁻ is well conserved during cluster-assembly, characteristic of a “superatom”. This study should be helpful in understanding the hetero-doped assembly mechanism of the ptC chemistry. Moreover, the present results are expected to enrich the flat carbon chemistry, superatom chemistry, metallocenes and combinational chemistry. Electronic Supplementary Material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Sandwich compounds of second-row elements: A quantum chemical study

The structures and stabilities of a number of neutral and charged sandwich-type boron, carbon, and nitrogen compounds designed based on the cyclophane cage and obeying the “electron octet” rule were studied by the B3LYP/6−311+G** density functional method. The possibility of targeted modification of the electronic structures of such compounds by varying the basal or bridging atomic groups was investigated. Dedicated to Academician O. M. Nefedov on the occasion of his 75th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1825–1835, November, 2006.     

Integral invariants for high-symmetry open-shell molecules.

A numerical procedure for expanding electron repulsion integrals 〈mm|nn〉 on degenerate molecular orbitals of γ symmetry (γ=e, t, g, h) into integral invariants (reduced matrix elements) H^k(γ, γ) is suggested. The latter are analogous in their sense to Slater-Condon parameters F^k(l, l) for atoms with an electronic configuration l^N. The method is applicable to nonlinear molecules of arbitrary symmetries, including “not readily reducible” groups. G. K. Boreskov Institute of Catalysis, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 39, No. 1, pp. 3–17, January–February, 1998. This work was supported by RFFR grants No. 96-03-01167 and 96-03-34035.