Resonant multiphoton dissociation of the NO molecule

The multiphoton dissociation of an unexcited NO molecule involving intermediate Rydberg states n?σ(²∑⁺), n?π(²П), and n?δ(²Δ), which are populated by a weak probe field and decay owing to nonadiabatic transitions in the predissociation states of valence configurations B′²Δ, L ²П, I ²∑⁺, and B ²П, has been studied. The role of the ponderomotive interaction that occurs under the simultaneous action of an intensive electromagnetic monochromatic radiation on the studied system has been analyzed. A theory to describe the dynamics of the process has been described. The possibilities of laser stimulation of this process, which consist in the search for ranges of variation in the frequencies and intensities of laser radiation that provide the highest efficiency of the resonant photostimulated process, have been discussed.     

Multiphoton transitions and the resonant optical Stark effect in AgBr nanocrystals

Nonlinear absorption of 30-ps light pulses with λ = 560 nm in AgBr nanocrystals is experimentally studied in the range of intensities 10⁸–10¹⁰ W/cm². The results of a theoretical analysis show that the absorption is related to direct interband n-photon transitions. With increasing light intensity j, the number n increases and the region of the k-space changes for the transitions predominantly contributing to the absorption. It is shown that, due to specific features of the AgBr electronic band structure, the probabilities of two-photon transitions for the light at λ = 560 nm are anomalously low, while those of four-photon transitions are anomalously high. In addition, the increase in the two-photon transition rate with increasing intensity is blocked at j ? 10⁸ W/cm² due to the resonant optical Stark effect and due to a gap arising in the band spectrum, rearranged because of the interaction with light.     

PBE–DFT theoretical study of organic photovoltaic materials based on thiophene with 1D and 2D periodic boundary conditions

Conjugated organic systems such as thiophene are interesting topics in the field of organic solar cells. We theoretically investigate π-conjugated polymers constituted by n units (n = 1–11) based on the thiophene (Tn) molecule. The computations of the geometries and electronic structures of these compounds are performed using the density functional theory (DFT) at the 6–31 G(d, p) level of theory and the Perdew–Burke–Eenzerhof (PBE) formulation of the generalized gradient approximation with periodic boundary conditions (PBCs) in one (1D) and two (2D) dimensions. Moreover, the electronic properties (HOCO, LUCO, E _gap, V _oc, and V _bi) are determined from 1D and 2D PBC to understand the effect of the number of rings in polythiophene. The absorption properties—excitation energies (E _ex), the maximal absorption wavelength (λ_max), oscillator strengths, and light harvesting—efficiency are studied using the time-dependent DFT method. Our studies show that changing the number of thiophene units can effectively modulate the electronic and optical properties. On the other hand, our work demonstrates the efficiency of theoretical calculation in the PBCs.     

Specific features of photoprocesses in the dye merocyanine 540 and its complexes with water

The electronic structure and spectral-luminescence properties of the dye merocyanine 540 have been calculated within the framework of the semiempirical quantum-chemical method of partial neglect of differential overlap (PNDO) with spectroscopic parameterization. The trans and cis conformations of the molecule, as well as the trans–cis photoisomerization process, have been considered. The calculation has been performed for an isolated molecule of the merocyanine 540 and its complex with water. The results of the calculation have been compared with the experimental spectral-luminescence characteristics of the molecule in different solvents. It has been shown that there is a good agreement between the calculated and experimental spectra, the nature of the excited states, and photoprocesses.     

<Emphasis Type="Italic">Ab initio</Emphasis> theory of the electronic structure and spectra of impurity <Emphasis Type="Italic">nl</Emphasis> ions

The fundamentals of the theory of the electronic structure of impurity clusters and the results of numerical calculations for the iron-, lanthanum-, and actinium-group ions in Me⁺ⁿ: [L]_k clusters are presented. The effects of the interionic distance and ligands in the Me⁺ⁿ: [L]_k clusters on the electronic structure of the nl ^N and nl^N?1n′l′ configurations of the 3d, 4f, and 5f ions are considered. The correspondence between the optical and x-ray spectra of different impurity crystals is also analyzed.     

Resonant tunneling effect in one-dimensional twinned lattice photonic crystal under total reflection conditions

Under total reflection conditions, it typically seems as though light waves will be reflected completely on the interface; in actuality, the waves can penetrate the medium as evanescent waves. In this paper, we present a twinned lattice photonic crystal with a unit cell composed of AB layers and their mirror. We assume that the refractive index n ₀ of the input and output end is equal to n _B and larger than n _A . We first demonstrate the dependence of band structure on the incidence angle and normalized wavelength, in which the resonant tunneling bands are exposed. We then draw a comparison of bands between ABBA and AB. To conclude, we discuss the resonant tunneling effect in the twinned lattice photonic crystal under the total reflection conditions. As incidence angle increases, the resonant tunneling band ultimately vanishes completely.     

New emission spectrum of the TeO molecule

The spectrum of Tellurium monoxide as excited in a heavy current arc run by a 2000 volt D.C. generator was studied in the visible and ultraviolet regions. Photographs of the spectrum revealed many new bands in the regionλ 6200 toλ 3300, which are clearly degraded to longer wavelengths. Some of the bands in the regionλ 3800 toλ 3300 were identified with those of the system in the regionλ 3800 toλ 3060 (here designated as system,B-X) observed and analysed byChoong Shin Piaw. The analysis of theB-X system was extended to include some of the new bands uptoλ 4500. In addition to those assigned toB-X system, a number of new bands in the regionλ 5000 toλ 3500 constitute another system designated asA-X system. The analysis of this system has led to the following quantum formula for the band heads.v=27835+408 (v′+1/2)?4·0(v′+1/2)² ?796 (v″+1/2)+3·5 (v″+1/2)². The lower state of the two systems is common and is identified as the ground state of the TeO molecule. Bands in the regionλ 6200 to 5000 were analysed as belonging to another brief system. This system appears to arise from a transition between two escited states of the TeO molecule. The nature and properties of electronic terms responsible for the observed electronic states of the TeO molecule were discussed along with those of the related molecules O₂, SO, and SeO from considerations of electron configurations.     

A quantum-chemical study of the spectral and luminescent properties and photolysis of methyl[(4-aminophenyl)sulfonyl]carbamate

The spectral and luminescent properties and the photolysis of a neutral form of the isolated molecule of methyl[(4-aminophenyl)sulfonyl]carbamate (asulam) are interpreted with the aid of methods of quantum chemistry using the theory of intramolecular photophysical processes. It is shown that the breaking of the C-S bond in the molecule occurs according to the predissociation mechanism and is most efficient in the state T(πσ*_CS). The photoinduced breaking of the N-S bond occurs according to the same mechanism and is most efficient in the state S(nπ_NS).     

Multiphoton intraband absorption of femtosecond light pulses in crystals: II. Processes with the participation of acoustic and optical phonons

For arbitrary integers n, we have calculated probabilities P _n of n-photon intraband transitions with the participation of longitudinal acoustic and longitudinal optical phonons. Dependences of P _n on the duration of femtosecond pulses have been obtained. These dependences differ from those that are observed in the case of quasisteady electromagnetic radiation.     

Field-theory methods in coagulation theory

Coagulating systems are systems of chaotically moving particles that collide and coalesce, producing daughter particles of mass equal to the sum of the masses involved in the respective collision event. The present article puts forth basic ideas underlying the application of methods of quantum-field theory to the theory of coagulating systems. Instead of the generally accepted treatment based on the use of a standard kinetic equation that describes the time evolution of concentrations of particles consisting of a preset number of identical objects (monomers in the following), one introduces the probability W(Q, t) to find the system in some state Q at an instant t for a specific rate of transitions between various states. Each state Q is characterized by a set of occupation numbers Q = {n ₁, n ₂, ..., n _g , ...}, where n _g is the total number of particles containing precisely g monomers. Thereupon, one introduces the generating functional Ψ for the probability W(Q, t). The time evolution of Ψ is described by an equation that is similar to the Schrödinger equation for a one-dimensional Bose field. This equation is solved exactly for transition rates proportional to the product of the masses of colliding particles. It is shown that, within a finite time interval, which is independent of the total mass of the entire system, a giant particle of mass about the mass of the entire system may appear in this system. The particle in question is unobservable in the thermodynamic limit, and this explains the well-known paradox of mass-concentration nonconservation in classical kinetic theory. The theory described in the present article is successfully applied in studying the time evolution of random graphs.     

Faraday effect in alkali-metal vapors in a strong bichromatic field of laser light

Results of a numerical study of the Faraday effect arising upon propagation of the light beams with the frequencies ω _L1 (resonant to the nS _1/2-nP _{1/2, 3/2} transitions) and ω _L2 (resonant to the nP _{1/2, 3/2}-(n+2)S _1/2 transitions) through alkali-metal vapors are presented. Characteristics of the magneto-optical rotation spectra at each of the frequencies are strongly affected by the second intense radiation field resonant to the adjacent transition. When the atoms interact with two strong light waves, resonant to adjacent transitions, and with a magnetic field, the shape of the Faraday rotation spectra depends on the energy shifts of the atomic states that arise due to the dynamic Stark effect and the Zeeman effect (the Paschen-Back or an intermediate-type effect), as well as due to the difference of populations of these states caused by the interaction of the atoms with the fields. The results obtained show that in the frequency selection method, based on the resonance Faraday effect, the frequency of the generated narrow-band beam can be tuned by the intensity of the strong wave, resonant to the transition between the excited states.     

Spin-Wave Resonance in Ge : Mn Thin Films with Percolation Magnetic Ordering

The mechanism of excitation and propagation of spin waves in Ge: Mn thin films with different nominal manganese concentrations (2, 4, and 8 at % Mn) with percolation magnetic ordering is explored. Concentration dependencies of Curie temperature T_C(n) and spin wave rigidity D(n) are determined, which enables to find the index of correlation distance. An exotic percolation magnetic state of samples of Ge: Mn thin films is confirmed by rectifying experimental dependences D(n) and D/T_C(n) in coordinates accepted in the percolation theory.     

Congratulations to Akusticheskii Zhurnal on the occasion of its 50th anniversary. Vibrations of spherical inclusions in elastic solids

Variational principles are derived for the analysis of dynamical phenomena associated with spherical inclusions embedded in homogeneous isotropic elastic solids. The starting point is Hamilton’s principle, with the material properties assumed to vary only with the radial distance r from the origin. Attention is restricted to disturbances that are symmetric about the polar (z) axis, such that the nonzero displacement components in spherical coordinates, u _r and u_θ, are independent of the polar coordinate φ. The symmetry allows for a decoupling of the polar components, the nth of which is described by U _{r, n} (r, t)P _n (cosθ) and U_{θ, n}(r, t)dP _n /dθ. A variational principle is subsequently derived for the field quantities U _{r, n} and U_{θ, n}. Concepts analogous to those of the theory of matched asymptotic expansions are used to embellish the principle in order to allow for the damping associated with the outward radiation of elastic waves. Examples illustrating the use of the variational principle for formulating plausible lumped-parameter models are given for the cases of n = 0 and n = 1.     

Superlattices consisting of “lines” of adsorbed hydrogen atom pairs on graphene

The structures and electron properties of new superlattices formed on graphene by adsorbed hydrogen molecules are theoretically described. It has been shown that superlattices of the (n, 0) zigzag type with linearly arranged pairs of H atoms have band structures similar to the spectra of (n, 0) carbon nanotubes. At the same time, superlattices of the (n, n) type with a “staircase” of adsorbed pairs of H atoms are substantially metallic with a high density of electronic states at the Fermi level and this property distinguishes their spectra from the spectra of the corresponding (n, n) nanotubes. The features of the spectra have the Van Hove form, which is characteristic of each individual superlattice. The possibility of using such planar structures with nanometer thickness is discussed.     

Integral characteristics of vibronic-spin-orbit interactions in a phosphorus-containing analogue of the fluorene molecule

The strengths (P ₀₀ ^s )² and F _VSO ² of the transitions from the triplet sublevels s = z, y, and x of the electronic state ³A″ of the phenyldibenzophosphole (DB(P-Ph)) molecule are calculated taking into account the intramolecular spin-orbit (SO) and joint vibronic-spin-orbit (VSO) interactions. The contributions to the vibronic transition strengths from the SO interactions in different structural elements of the molecule (the C atoms of the dibenzene framework, the P atom, and the Ph substituent) are determined. The effect of the nonplanar nuclear configuration of the DB(P-Ph) molecule on the values of F _VSO ^s is investigated. The radiative deactivation rate constants of the k _rad ^s triplet sublevels T ^s are estimated. It is found that the vibrations of the A′(B₁) symmetry in the fine-structure phosphorescence spectrum of DB(P-Ph) occur due to both the SO coupling exclusively in the P atom and the T ^x → S₀ transition (the x axis is perpendicular to the planar dibenzene framework of the molecule) with a high (preferential) population of this triplet sublevel.     

Donor-Acceptor Conjugated Linear Polyenes: A Study of Excited State Intramolecular Charge Transfer,Photoisomerization and Fluorescence Probe Properties

Numerous studies of donor-acceptor conjugated linear polyenes have been carried out with the goal to understand the exact nature of the excited state electronic structure and dynamics. In this article we discuss our endeavours with regard to the excited state intramolecular charge transfer, photoisomerization and fluorescence probe properties of various donor-acceptor substituted compounds of diphenylpolyene [Ar(CH = CH) _n Ar] series and ethenylindoles.     

Direct observation of proton transfer from the excited <Emphasis Type="Italic">S</Emphasis><Subscript>2</Subscript> state in the 3-hydroxyflavone molecule

The spectra of dual fluorescence of 3-hydroxyflavone molecules excited by 44-ps pulses in the region of the S ₁ and S ₂ absorption bands are measured with a picosecond resolution. The dynamics of the spectra directly demonstrates the time development of the proton transfer from the carboxyl to the carbonyl group of the molecule. Upon excitation into the main absorption band, the transfer process occurs for about 210 ps. The excitation into the region of the S ₂ band results in a faster (～170 ps) process, and the relative contribution made to the total spectrum by the long-wavelength band, which belongs to the proton-transfer state, is higher in this case for all the time ranges of luminescence recording. The data obtained directly point to an additional channel of proton transfer via the S ₂ state. The probability of this process is estimated to be 0.84 × 10¹² s^?1.