Association of tert-butyl alcohol: a matrix infrared study

Infrared spectra of (CH₃) ₃COH, (CH₃)₃COD, (CD₃)₃COH and (CD₃)₃COD have been studied in the liquid and solid states, in CCl₄ and CS₂ solutions, and in argon, krypton and nitrogen matrices. The Raman spectra of the solids and of CCl₄, and H₂O solutions have been recorded. The matrix infrared results show that in the matrices tert-butyl alcohol has two well-defined dimer associates, both of which seem to have an open-chain structure. A network is proposed for the higher associates. The relative strengths of the protium and deuterium bonds are discussed in terms of the monomer hydroxyl-stretching frequencies and the Δv shifts. Association characteristics of the most important fundamental bands in several spectra are given.     

Internal structure of neutron stars

The equation of state and the structure and composition of neutron star matter are investigated in the density region 3.1 × 10¹¹−2 × 10¹⁵g/cm³. Below the density 3.1 × 10¹¹ g/cm³ the matter is a solid consisting of neutron-rich nuclei in a degenerate electron gas. At 3.1 × 10¹¹g/cm³ neutrons start to drip out of the nuclei; as the density increases, the lattice spacing continuously decreases while the geometrical size of the nuclei only slightly increases, until at about 15 × 10¹³g/cm³ the nuclei disappear by coalescing into a homogeneous liquid in an almost continuous phase transition. The maximum proton number per nucleus is 40, which is obtained between the densities 1−2.5 × 10¹³g/cm³; after that the proton number decreases until at the solid-to-liquid phase boundary it is about 20. In the liquid-core region, muons appear at the density 20.5 × 10¹³g/cm³.     

Quantum chemical simulation of excited states of chlorophylls, bacteriochlorophylls and their complexes

The present review describes the use of quantum chemical methods in estimation of structures and electronic transition energies of photosynthetic pigments in vacuum, in solution and imbedded in proteins. Monomeric Mg-porphyrins, chlorophylls and bacteriochlorophylls and their solvent 1:1 and 1:2 complexes were studied. Calculations were performed for Mg-porphyrin, Mg-chlorin, Mg-bacteriochlorin, mesochlorophyll a, chlorophylls a, b, c(1), c(2), c(3), d and bacteriochlorophylls a, b, c, d, e, f, g, h, plus several homologues. Geometries were optimised with PM3, PM3/CISD, PM5, ab initio HF (6-31G*/6-311G**) and density functional B3LYP (6-31G*/6-311G**) methods. Spectroscopic transition energies were calculated with ZINDO/S CIS, PM3 CIS, PM3 CISD, ab initio CIS, time-dependent HF and time-dependent B3LYP methods. Estimates for experimental transition energies were obtained from linear correlations of the calculated transition energies of 1:1 solvent complexes against experimentally recorded solution energies (scaling). According to the calculations in five-coordinated solvent complexes the magnesium atom lies out of the porphyrin plane, while in six-coordinated complexes the porphyrin is nearly planar. Charge densities on magnesium and nitrogen atoms were strongly dependent on the computational method deployed. Several dark states of low oscillator strength below the main Soret band were predicted for solvent complexes and chlorophylls and bacteriochlorophylls in protein environment. Such states, though not yet identified experimentally, might serve as intermediate states for excitation energy transfer in photosynthetic complexes. Q(y), Q(x) and Soret transition energies were found to depend on the orientation of the acetyl group and external pressure. A method to estimate site energies and dimeric interaction energies and to simulate absorption and CD spectra of photosynthetic complexes is described. Simulations for the light harvesting complexes Rhodospirillum molischianum, chlorosomes of Chlorobium tepidum and Chloroflexus aurantiacus, and LHC-II of Spinacia oleracea are presented as examples.     

Independent-cluster methods as mappings of quantum theory into classical mechanics

Summary The algebraic structures of theconfiguration interaction, normal coupled cluster, andextended coupled cluster methods are reviewed and developed. These methods are pointed out to perform a mapping of the quantum mechanical problem into a classical phase space, where in each case the classical canonical coordinates have characteristically different cluster and locality properties. Special focus is given to the extended coupled cluster method (ECCM), which alone is based on an entirely additively separable coordinate system. The general principles are formulated for systems with both bosonic and fermionic degrees of freedom, allowing both commutative and anticommutative (Grassmann) cluster amplitudes. The properties of the classical images are briefly discussed. It is proposed that phase spaces may exist which are fixed points of quantization.Based on a talk given at theWorkshop on Coupled-Cluster Theory at the Interface of Atomic Physics and Quantum Chemistry, Harvard-Smithsonian Institute for Theoretical Atomic and Molecular Physics, Cambridge, MA, August 7–11, 1990     

Dependence of variables construed as an atomic formula

We define a logic D capable of expressing dependence of a variable on designated variables only. Thus D has similar goals to the Henkin quantifiers of [4] and the independence friendly logic of [6] that it much resembles. The logic D achieves these goals by realizing the desired dependence declarations of variables on the level of atomic formulas. By [3] and [17], ability to limit dependence relations between variables leads to existential second order expressive power. Our D avoids some difficulties arising in the original independence friendly logic from coupling the dependence declarations with existential quantifiers. As is the case with independence friendly logic, truth of D is definable inside D. We give such a definition for D in the spirit of [11] and [2] and [1].     

Analysis of the time structure of the GLE on February 16, 1984

Summary The time structure of the ground-level event on February 16, 1984 was studied by using 30 s data of the Turku double neutron monitor. The onset time of the event was found to be (09:06:00±1) min U.T. The time between the injection of protons from the flare site and release of relativistic particles into interplanetary space was (6÷7) min. The linear rise rate of the event at Turku was 5.4%/min and the rise time (5±1) min. The event was complicated in structure consisting of at least two separate pulses of particles, the first lasting for about 14 min and the second about 8 min.

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Riassunto Si è studiata la struttura dell'evento a livello del suolo verificatosi il 16 Febbraio 1984 usando i dati a 30 s del doppio monitor neutronico Turku. Si è trovato che il tempo all'inizio dell'evento a Turku era (09:06:00±1) min U.T. Il tempo tra l'iniezione di protoni dal sito di brillamento e il rilascio di particelle relativistiche nello spazio interplanetario era di (6÷7) min. Il tasso lineare d'incremento dell'evento a Turku era di 5.4%/min e il tempo di incremento era di (5±1) min. L'evento era complicato nella sua struttura, che consiste in almeno due impulsi separati di particelle, il primo di durata di circa 14 min e il secondo di circa 8 min.

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Резюме Исследуется временная структура события на уровне земли 16 февраля 1984 г., используя 30-секундные данные с двойного нейтронного монитора в Турку. Время начала события составляет 09:06:00±1 минут U.T. Время между инжекцией протонов от места вспымки и высвобождением релятивистских частиц в межпланетное пространство составило (6÷7) минут. Линейная скорость возрастания события в Турку была 5.4%/мин, а время возрастания было (5±1) минут. Это событие имело сложную структуру, которая состоит, по крайней мере, из двух изолированных импульсов частиц, первый имеет продолжительность около 14 минут, а второй—около 8 минут.

     

Electron ionization and chemical ionization fragmentation of o/p isomers of bisphenol-A with tandem mass spectrometry

The fragmentation of o/p isomers of bisphenol-A was examined by using collisionally activated decomposition and the tanden mass spectrometric techniques. Also chemical ionization was performed using methane, isobutane and ammonia. The o/p position of the hydroxy groups in the bisphenol-A molecule directed the fragmentation both in electron and chemical ionization.     

Anodic stripping voltammetry with a symmetric double-step waveform

The high sensitivity of differential pulse anodic stripping voltammetry (d.p.a.s.v.) is based on discrimination against the charging current by using short current-sampling periods near the end of the applied pulses. In this paper, the capacitive current is eliminated by using a symmetric double-step waveform superimposed on the voltage ramp. The areas under the adjacent current peaks are subtracted from each other which effectively cancels the contribution of the double-layer charging current but preserves the changes in the faradaic current. By using a mercury thin-film electrode the base line is reasonably flat down to nanomolar levels of Cd, Cu and Pb with a deposition time of 3–5 min. Compared with d.p.a.s.v., the proposed method has the advantages of a higher scan rate and simple electronic circuitry.     

Photoinduced ultrafast dye-to-semiconductor electron injection from nonthermalized and thermalized donor states.

Electron injection from the transition metal complex Ru(dcbpy)(2)(NCS)(2) (dcbpy = 4,4'-dicarboxy-2,2'-bipyridine) into a titanium dioxide nanocrystalline film occurs on the femto- and picosecond time scales. Here we show that the dominating part of the electron transfer proceeds extremely rapidly from the initially populated, vibronically nonthermalized, singlet excited state, prior to electronic and nuclear relaxation of the molecule. The results are especially relevant to the understanding and design of molecular-based photovoltaic devices and artificial photosynthetic assemblies.