Reactions of HBr+ ions in the 2Π i , v + quantum states with H2 and HBr molecules

The mechanisms and kinetics of low-temperature ion-molecular reactions between the Br⁺, HBr⁺, and DBr⁺ions and the HBr, DBr, H₂, and D₂ molecules were studied. The HBr⁺ (i,v ⁺) and DBr⁺(i,v ⁺) ions were prepared in separate spin-orbit (i) and vibrational (v ⁺) states by resonance multiphoton ionization in a free flow of halogen halides (HBr and/or DBr) with hydrogen, deuterium, or inert gases (Ar, He). The effectiveness of various reaction channels, including the exchange of charges, H and D atoms, and H⁺andD⁺ ions, was studied. The quantitative data on the kinetics of these reactions were obtained for separate quantum states of the ions. The resonance ionization of one of the two ion isotopomers H⁷⁹Br⁺(D⁷⁹Br⁺) or H⁸¹Br⁺(D⁸¹Br⁺) was used to study and compare the effectiveness of various ion-molecular reaction channels.     

Accurate thermochemistry from quantum chemical calculations?

The answer to the title question is definitely “yes” – at least for fairly small molecules. Computational procedures, namely the Weizmann (Wn) and Gaussian-3 (G3) family of methods, the complete basis set extrapolation scheme (CBS-x), the “high accuracy extrapolated ab initio thermochemistry” (HEAT) as well as the “correlation consistent composite approach” (ccCA), aimed at energies with chemical accuracy or even better (sub kJ?mol^?1) are described and several applications illustrating the level of accuracy that can be achieved are presented.     

Introducing the γ function in quantum theory

Through a series of postulates, we define a function γ(x) whose square acts as Dirac's δ(x) and exhibits several unusual properties. Though the square root of δ cannot be defined among distributions, it appears in quantum theory if one wants to associate a wave function to a (quasi)classical particle having charge distribution δ(x) . The newly defined function γ(x) serves to describe quasi-classical particles using part of the quantum formalism (eg, wave functions, operators, expectation values) but exhibiting classical properties. The function γ(x) appears to be useful to define model wave functions for simple (quasi)quantum systems. In a spherical coordinate system, γ(r − r₀) leads to a quasi-classical “bubble” model of the hydrogen atom, where the electron is distributed on the surface of a sphere with radius r₀, and it provides exact quantum mechanical energies of its total symmetric levels. For other simple quantum systems, it provides approximate but meaningful energies. In particular, exact energy differences for harmonic oscillator levels are obtained, with the zero-point energy missing.     

Average energy and quantum similarity of a time dependent quantum system subject to Pöschl–Teller potential

Journal of Mathematical Chemistry - Exact solutions of time-dependent Schrödinger equation in presence of generalized Pöschl–Teller like potential plus oscillator potential are...     

Wavelets—something for quantum chemistry?

We propose to use the relatively new mathematical and numerical tool wavelets in quantum chemical studies. A short survey is given of the most elementary aspects of wavelet theory. The connection between wavelets and coherent states is discussed together with Zak's so-called kq-representation. © 1996 John Wiley & Sons, Inc.     

Are there quantum beats from vacuum-induced coherence?

In a recent paper by Hegerfeldt and Plenio [1] it has been argued that for a certain class of V-level systems quantum beats could be observed even if the system was not in a coherent superposition of the upper levels. The beat frequency would be different to the upper level splitting. In their analysis, this was an effect of the quantum vacuum field which generated a coherent superposition of the upper levels in the course of the interaction. Their derivation is reanalyzed here using standard techniques which lead to a master-equation. Calculating the weak probe absorption spectrum, one finds that — as expected — the experimentally accessible, physical levels are the eigenstates of the combined system consisting of the atom and the vacuum which by definition do not couple. Thus, a coherent superposition will not be generated starting from a true, renormalized upper state and therefore quantum beating will only occur if an initial coherent superposition of renormalized upper levels is provided.This article was processed by the author using the LAT_EX style filepljour2 from Springer-Verlag.     

Excited Π states of divinyl chalcogenides and chalcophenes

Electron transitions in divinyl chalcogenides (CH₂=CHXCH=CH₂, where X is S, Se, or Te) have been analyzed using UV absorption spectra of dialkyl and alkyl vinyl chalcogenides. The following relations for the orbital energies are found: ^* < ^* < ^* < ^* for Te and ^* < ^* < ^* < ^* for S and Se. For chalcophenes, a correlation between the energy of the excited state (E ^*) of specific symmetry, the ionization potential (I) and the electron affinity (EA) is obtained:E ^*=const+(I+EA)/2. The electron affinity of divinyl chalcogenides is estimated. The correlation between the excited ^* states of divinyl chalcogenides and chalcophenes is discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 831–835, May, 1994.     

Padé spectrum decompositions of quantum distribution functions and optimal hierarchical equations of motion construction for quantum open systems

Pade? spectrum decomposition is an optimal sum-over-poles expansion scheme of Fermi function and Bose function [J. Hu, R. X. Xu, and Y. J. Yan, J. Chem. Phys. 133, 101106 (2010)]. In this work, we report two additional members to this family, from which the best among all sum-over-poles methods could be chosen for different cases of application. Methods are developed for determining these three Pade? spectrum decomposition expansions at machine precision via simple algorithms. We exemplify the applications of present development with optimal construction of hierarchical equations-of-motion formulations for nonperturbative quantum dissipation and quantum transport dynamics. Numerical demonstrations are given for two systems. One is the transient transport current to an interacting quantum-dots system, together with the involved high-order co-tunneling dynamics. Another is the non-Markovian dynamics of a spin-boson system.     

Fluorescence quantum yields of α, ω-diphenylpolyenes

Absolute fluorescence quantum yields of trans-stilbene and all-trans α, ω-diphenylpolyenes with the polyene double-bond number (n) from two to six have been determined in a room-temperature solvent. The 1¹Bu-fluorescence yield measured as a function of the polyene chain length shows a maximum for n = 2, while the 2¹Ag-fluorescence yield shows a maximum for n = 3, and both yields decrease with further increase of n. The observed quantum yield behavior is discussed briefly.     

A dynamical Lie algebraic mehtod for quantum reactive scattering

Ｒａｐｉｄｐｒｏｇｒｅｓｓｉｎｔｈｅｔｈｅｏｒｙｏｆｑｕａｎｔｕｍｒｅａｃｔｉｖｅｓｃａｔｔｅｒｉｎｇｈａｓｂｅｅｎｍａｄｅｉｎｔｈｅｐａｓｔｆｅｗｙｅａｒｓ.Ａｓａｒｅｓｕｌｔｏｆｔｈｅｐｒｏｇｒｅｓｓｏｎｅｃａｎｎｏｗｃａｌｃｕｌａｔｅｅｘａｃｔｓｔａｔｅ＿ｔｏｓｔａｔｅｒｅａｃｔｉｏｎｃｒｏｓｓｓｅｃｔｉｏｎｓｆｏｒａｆｅｗｆｕｎｄａｍｅｎｔａｌｒｅａｃｔｉｏｎｓ.Ａｍｏｎｇｖａｒｉｏｕｓｆｏｒｍｕｌａｔｉｏｎｓｏｆｔｈｅｔｈｅｏｒｅｔｉｃａｌａｐｐｒｏａｃｈ,ｔｈｅＳｍａｔｒｉｘＫｏｈｎｖ…     

Computational determination of the à state absorption spectrum of NH3 and of ND3 using a new quasi-diabatic representation of the X and à states and full six-dimensional quantum dynamics

A recently developed method to represent adiabatic electronic states coupled by conical intersections has been used to construct a full six-dimensional quasi-diabatic representation of the 1(1)A and 2(1)A states of NH(3). This representation is expected to be appropriate to simulate the photodissociation of ammonia when it is excited to the 2(1)A electronic state. In this work, the electronic structure aspects of this quasi-diabatic representation are analyzed. This representation is then used as the basis for a simulation of the ? ← X absorption spectrum, dominated by a progression in the v(2) mode, using a full six-dimensional quantum mechanical treatment of the nuclear motion. Results are reported for both NH(3) and ND(3). This simulation provides the most accurate computational determination of this absorption spectrum reported to date. These results serve to validate the quasi-diabatic representation and set the stage for subsequent studies of vibrationally mediated photodissociation of NH(3).     

Are intermediate electronic states responsible for pyroelectric luminescence?

Patel and Hanson have observed discrete spectrum-like spontaneous luminescence of, and simultaneous current flow through, certain organic and ionic crystals when they were either cooled or heated at a constant rate. The hypothetical intermediate electronic states (neither bulk nor localized-type) are thought to be responsible for this effect. By the “turning over process”, these states can transport a definite quantity of electric charge through the crystal for special discrete (size, shape, surface contamination, temperature and pressure dependent) boundary conditions, even if the crystal is a semiconductor or insulator.     

Comment: Electron-transfer reactions in the 9-mesityl-10-methylacridinium ion: impurities, triplet states and infinitely long-lived charge-shift states?

The likelihood of an infinitely long-lived, charge-shift state being formed by the target compound is re-assessed in light of persistent claims that such chemistry is both viable and observable.     

A new perspective on transition states: χ1 separatrix

We present a new definition of the transition state for chemical reactions, named the χ(1) separatrix. In contrast to previous transition state definitions which depend on the choice of reaction coordinates, the χ(1) separatrix is defined by choosing a time scale for observation and is connected to exact rate constants in the high friction limit. We demonstrate that this separatrix appears in the isomerization of alanine dipeptide as a stationary population in quasi-equilibrium, without assuming a particular coordinate system or reactant and product surfaces.     

Potential energy surfaces for low-lying electronic states of SO_2

The sulfur dioxide molecule (SO2) is an important atmospheric pollutant primarily from sulfur-containing materials combustion processes[1]. Because of its im- portance in atmospheric photochemistry, as well as in atmospheric dynamics, this molecule has been the subject of much experimental[2―10] and theoreti- cal[11―19] photochemical study for many years. They provide a wealth of information about the SO2 spec- trum, predissociation mechanism, vibration including vibration-rotation interact…     

Effects of liquid crystal states on photovoltaic effects of chlorophyll-a

The photovoltaic effects of chlorophyll-a(chla) and the effects of stearic acid, egg phosphatide and cholesterol on those were investigated by means of measuring the photoinduced potentials of SnO2/chla electrodes. Because of the formation of liquid crystal states, appropriate concentrations of stearic acid and egg phosphatide added in a certain system could increase the photovoltaic effects of chla. Cholesterol always decreased the photovoltaic effects of chla because there was no liquid crystal state formed with it.