The dynamic structure of <Emphasis Type="Italic">cis</Emphasis> and <Emphasis Type="Italic">trans</Emphasis> conformers of substituted phosphinous acids

The potential energy surfaces of bis-(trifluoromethyl)-phosphinous (III), diemthylphosphinous (IV), and bis-(pentafluorophenyl)-phosphinous (V) acids, the geometric parameters of the cis and trans conformers of these acids, and their P-O and O-H stretching vibration frequencies were calculated by the density functional theory method (PBE, 4Z). The potential energy surface sections corresponding to internal rotations about the P-O bonds were constructed, and dynamic problems for such a motion of the proton in a cyclic potential were solved by the Ritz method using a basis set of 100 trigonometric functions. According to calculations, the energy differences between the cis and trans conformers of acids III–V were of 4–7 kJ/mol, and the heights of potential barriers separating these conformers were of from 11 to 16 kJ/mol. In acids III and V, the cis, and, in IV, the trans conformer was stabler. At 298 K, only the ground vibrational states were populated for both rotamers of IV and V and the cis conformer of III. The special features of the potential of III were such that, at 298 K, the first excited vibrational level of its trans conformer was also noticeably populated.     

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.     

Fluorescence of the <Emphasis Type="Italic">cis</Emphasis>-dimers of porphyrins containing ethylene bridges

The absorption and fluorescence spectra of solutions of the porphyrin dimers containing ethylene bridges, binding two Zn(II)octaethylporphyrin molecules or one Zn(II)octaethylporphyrin and one octaethylporphyrin molecule into cis conformation, were studied. For both studied cis-dimers, structureless absorption spectra were observed, only in general resembling the spectra of initial molecules, as well as weak fluorescence with a wide bell-shaped spectrum with a maximum at 680–700 nm and a quantum yield of about Φ_f≈3×10^?5, which is three orders of magnitude lower as compared to the fluorescence of initial monomeric porphyrins. A strong dependence of the fluorescence yield on a medium viscosity was revealed. In addition, low-yield irreversible cis-trans photoisomerization of cis-dimers was detected. A mechanism responsible for the strong intramolecular quenching of fluorescence of the porphyrin dimers containing ethylene bridges is suggested to be a conformation transformation in the region of the ethylene bridge, leading the molecular system to the region of “conic crossing” of the energy surfaces of excited and ground electron states.     

Recording of dynamic gratings in the nonlinear optical coating of a planar waveguide

The possibility of controlled energy exchange between interfering waveguide modes in a singlemode planar waveguide with a nonlinear optical coating is analyzed. As the coating, a suspension of bacteriorhodopsin D96N was used, which makes it possible to realize two spectrally separated mechanisms of recording and controlling dynamic gratings, i.e., the spatial modulation of the trans-cis excitation rate and the spatial modulation of the cis-trans relaxation rate. The method of phase-modulated beams was used to implement the energy exchange. The dynamic gratings in the coating were recorded by using both radiation with a wavelength within the absorption band of the trans state (630 nm) and radiation with a wavelength within the absorption band of the cis state (440 nm). Efficient control of the energy exchange between the waveguide modes by means of uniform exposure of their interference region to radiation with another wavelength was observed. A completely integral geometrical layout for optically controlled energy exchange was realized. The results obtained are compared with known data on energy exchange between beams in the bulk of a similar nonlinear medium.     

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.     

<Emphasis Type="Italic">cis</Emphasis> Versus <Emphasis Type="Italic">trans</Emphasis>-Azobenzene: Precise Determination of NMR Parameters and Analysis of Long-Lived States of <Superscript>15</Superscript>N Spin Pairs

We provide a detailed evaluation of nuclear magnetic resonance (NMR) parameters of the cis- and trans-isomers of azobenzene (AB). For determining the NMR parameters, such as proton–proton and proton–nitrogen J-couplings and chemical shifts, we compared NMR spectra of three different isotopomers of AB: the doubly ¹⁵N labeled azobenzene, ¹⁵N,¹⁵N′-AB, and two partially deuterated AB isotopomers with a single ¹⁵N atom. For the total lineshape analysis of NMR spectra, we used the recently developed ANATOLIA software package. The determined NMR parameters allowed us to optimize experiments for investigating singlet long-lived spin states (LLSs) of ¹⁵N spin pairs and to measure LLS lifetimes in cis-AB and trans-AB. Magnetization-to-singlet-to-magnetization conversion has been performed using the SLIC and APSOC techniques, providing a degree of conversion up to 17 and 24% of the initial magnetization, respectively. Our approach is useful for optimizing the performance of experiments with singlet LLSs; such LLSs can be exploited for preserving spin hyperpolarization, for probing slow molecular dynamics, slow chemical processes and also slow transport processes.     

Spectroscopy and photophysics of chloro-bis-bipyridyl complexes of ruthenium(II) with pyridine ligands

The absorption, luminescence, and luminescence excitation spectra of ruthenium(II) complexes cis-[Ru(bpy)₂(L)Cl]⁺[bpy=2,2′-bipyridyl; L=NH₃, pyrazine, pyridine, 4-aminopyridine, 4-picoline, isonicotinamide, 4-cyanopyridine, 4,4′-bipyridyl, or trans-1,2-bis(4-pyridyl)ethylene] in alcoholic (4: 1 EtOH-MeOH) solutions are studied. At 77 K, the quantum yields and decay times of the luminescence of the complexes are measured and the deactivation rate constants of the lowest electronically excited metal-to-ligand charge transfer state (³MLCT) are determined. The linear correlation between the energy of the lowest state ³MLCT d _π(Ru)>π*(bpy) of the cis-[Ru(bpy)₂(L)Cl]⁺ complexes and the parameter pK_a of the free 4-substituted pyridines and pyrazine used as ligands is established.     

Highly excited and autoionizing states in the spectrum of triply ionized titanium Ti(IV)

The spectrum of Ti(IV) excited in a vacuum spark was investigated in the range 250–900 Å with high resolution. Eighty-four lines were measured and identified as transitions from the 3p⁶ns, 3p⁶np, and 3p⁶nf configurations, where n ≤ 8, ≤ 10, and ≤ 8, respectively, and from the 3p⁵3d² and 3p⁵3d⁴s configurations. The lines due to the transitions from the autoionizing levels of the 3p⁵3d² and 3p⁵3d⁴s configurations were also observed and their widths were measured. The experimental data were compared with the results obtained by calculations using the Hartree-Fock method and semiempirical calculations.     

Schiff moment of the mercury nucleus and the proton dipole moment

The Schiff moment of the ¹⁹⁹Hg nucleus is calculated using finite range P-and T-violating weak nucleon-nucleon interaction. Both the contributions of the P-and T-odd interaction and of internal nucleon electric dipole moments to the Schiff moment of ¹⁹⁹Hg are calculated. The contribution of the proton electric dipole moment is obtained via core-polarization effects treated in the framework of RPA with effective residual interactions. We derive a new upper bound |d _p |<5.4×10^?24e cm for the proton electric dipole moment.     

Parameterization of the spectra of configurations 3<Emphasis Type="Italic">p</Emphasis>4<Emphasis Type="Italic">f</Emphasis> and 3<Emphasis Type="Italic">p</Emphasis>5<Emphasis Type="Italic">f</Emphasis> of a phosphorus ion P II. Gyromagnetic ratios

In the one-configuration approximation, in the formalism of irreducible tensor operators, and in the intermediate (real) coupling scheme, numerical values of the fine-structure parameters are determined for the 3p4f and 3p5f highly excited configurations of the P II phosphorus ion with the energy-operator matrix in the LK-coupling approximation. With these values of the fine-structure parameters, the energy-operator matrix is numerically diagonalized in the LS-coupling approximation. The gyromagnetic ratios calculated in both basis sets in the absence of a field are compared with one another, as well as with their vector counterparts and the experimental g-factors available for the 3p4f configuration. The experimental and theoretical g-factors calculated with the LS basis set are in good agreement with the sole exception of the ³ F ₂ level. Note that the calculation of g-factors from the Zeeman splitting in the linear region totally confirmed their agreement with the values calculated in the LS basis set (g _LS ) in the absence of a field. The gyromagnetic ratios are the main objectives of this and previous papers, especially for configurations for which experimental data are absent. Apart from the g-factors, the specific features of Zeeman splitting (the crossings and anticrossings of magnetic components) in the 3p5f configurations were determined. These data are to be compared with results of future experiments. Comparison of gyromagnetic ratios calculated in the intermediate coupling scheme with their vector counterparts showed that most levels of the configurations studied are closer than in the LK-coupling scheme.     

EPR and longitudinal response signals in spin systems consisting of localized (<Emphasis Type="Italic">s</Emphasis>=1/2) and delocalized spins

The spin system of many new promising materials, such as high-temperature superconductors, fullerenes, fullerides, or manganites with colossal magnetoresistance, consists of localized spins (s-spins of impurity paramagnetic centers) and delocalized spins (e-spins of charge carriers). The two sorts of spins are coupled by exchange interaction, which leads to coupled precession of the corresponding magnetizations. When the materials mentioned above are investigated by EPR methods, the measured longitudinal (T₁) and transverse (T₂) relaxation times provide the most valuable information. However, the presence of inhomogeneous broadening of the EPR of s-spins often makes it difficult to measure T₂, while small values of T₁ do not allow one to measure it by conventional methods. Atsarkin and colleagues [4, 7, 8] proposed a new version of the method for measuring T₁ by longitudinal response signals induced in a longitudinal spin coil (oriented along the constant magnetic field) under low-frequency modulation of the microwave power, which saturates the EPR, even though very weakly. Earlier, the results obtained in experiments on measuring the longitudinal response for samples containing interacting s-and e-spins were interpreted using formulas for an individual sort of spins. In this paper, the magnetization of s-and e-spins that precess under the condition of relaxational coupling is considered, which is characteristic, for example, of fullerides. The complete EPR susceptibility is represented in a form that makes it possible to determine the origin (from s-or e-spins) of two Lorentzians, each of which is characterized by one of the normal decay rates of two coupled oscillators (i.e., of precessing transverse magnetization components). The common EPR line analytically decomposed into those Lorentzians, and special factors take into account the influence of the other sort of spins on the amplitude of the signal generated by the sort under consideration. Similarly to the EPR absorption signals, the expressions for the longitudinal response are decomposed into parts originating from s-and e-spins, and each part is proportional to the form factor of one of the modes (s-or e-like). The qualitative comparison shows good agreement with experimental data in terms of EPR and longitudinal response in a fulleride.     

On the deexcitation of phonon excitations in nonspherical even-even nuclei by <Emphasis Type="Italic">M</Emphasis>1 transitions

The reasons for the violation of sign invariability for the parameter of mixture of M1 and E2 multipoles in the deexcitation of levels of the β-and γ-rotational bands to levels of the ground-state rotational band are considered for N = 90–114 nonspherical even-even nuclei.     

Manifestation of a strong quadrupole interaction and peculiarities in the SERS and SEHRS spectra of 4,4'-bipyridine

The paper analyzes Surface Enhanced Raman Scattering (SERS) and Surface Enhanced Hyper Raman Scattering (SEHRS) spectra of 4,4'-bypiridine molecule for two possible geometries, which are described by D ₂ and D _2h symmetry groups. It is pointed out on appearance of sufficiently strong lines, caused by vibrations with the unit irreducible representation for both possible configurations. Appearance of these lines in the SEHRS spectrum points out the existence of a strong quadrupole light-molecule interaction. In addition one observes the lines, caused by vibrations both with the unit irreducible representations A or A _g and the irreducible representation B ₁ or B _1u . The last ones describe transformational properties of the d _z component of the dipole moment, which is perpendicular to the surface. This property of the spectrum is caused by peculiarity of the geometry of the molecule, which consists of two benzene rings, which are weakly connected with each other. The linear combinations of the vibrations of the rings create two nearly degenerated symmetric and anti symmetrical states, which cannot be identified in the experimental spectra. The result is in a full agreement with the dipole-quadrupole theory of SERS and SEHRS.     

Die Spektren der Neutronen aus den Reaktionen C12(γ,n)C11 und O16(γ,n)O15

The (γ, n)-reactions on carbon and oxygen were studied using the 30,5 MeV brems-strahlung beam of the Heidelberg betatron. The photoneutrons were detected via the recoil protons in a stilbene scintillator. The pulse height spectrum of scintillations produced in the stilbene crystal by the recoil protons is analyzed to yield the incident neutron energy distribution. Theγ-ray and electron background was strongly reduced through pulse shape discrimination. To test the apparatus the spectrum of the neutrons from a Po-α-Be source was measured. The energy spectrum of the photo-neutrons from O¹⁶ shows clearly two peaks at excitation energies of 22,4 and 24,4 MeV also seen in the photo-proton spectra. The energy distribution of the neutrons from C¹² (γ, n) too contains indication of structure already known from the proton spectra from C¹² (γ, p). The derived cross sections of C¹² (γ, n ₀) and O¹⁶ (γ, n ₀) coincide as well in their shape as in their absolute magnitude with the corresponding (γ, p ₀)-cross sections. In both C¹² (γ, n) and O¹⁶ (γ, n)-reaction the neutrons seem to leave the final nucleus mainly in its ground state.     

Comment on the surface exponential for tensor fields

Starting from an essentially commutative exponential map E(B|I) for generic tensor-valued 2-forms B, which were introduced in [10] as a direct generalization of the ordinary noncommutative P exponent for 1 forms with values in matrices (i.e., in tensors of rank 2), we suggest a nontrivial but multiparametric exponential E(B|I|t_γ), which can serve as an interesting multidirectional evolution operator in the case of higher ranks. To emphasize the most important aspects of the article, the construction is restricted to the backgrounds I _ijk , which are associated with the structure constants of the commutative associative algebras, which make it insensitive to the topology of the 2D surface. Boundary effects are also eliminated (straightforward generalization is needed to incorporate them).     

Hadroproduction of heavy quarkonia at high energies within the <Emphasis Type="Italic">k</Emphasis><Subscript><Emphasis Type="Italic">T</Emphasis></Subscript>-factorization approach

On the basis of the k _T -factorization approach, heavy-quarkonium \((c\bar c,b\bar b)\) hadroproduction at high energies is considered within nonrelativistic QCD in the leading order in α _s and v. The p _T spectra of various S-and P-wave quarkonium states at the Tevatron collider energies (run I and run II) are fitted, and sets of octet nonperturbative matrix elements are obtained for three different versions of the noncollinear gluon distribution in the proton.     

Analysis of the spectrum of the Zn-like Kr VII ion: Highly excited 4<Emphasis Type="Italic">p</Emphasis>4<Emphasis Type="Italic">d</Emphasis> and 4<Emphasis Type="Italic">p</Emphasis>5<Emphasis Type="Italic">s</Emphasis> configurations

The spectrum of the Zn-like Kr VII ion, excited in a capillary discharge and recorded with a high resolution in the wavelength range of 300–1000 Å, was studied. Previously performed identification of the transitions from the levels of the 4s4f, 4s5s, 4s5p, and 4s5d configurations is confirmed and extended, and the energies of these levels are specified. The (4p ²+4s4d)?4p4d and (4p ²+4s5s)?4p5s transitions are identified for the first time, and the energies of all the levels of the 4p4d and 4p5s configurations are determined. The results of the analysis performed are confirmed by semiempirical calculations in terms of the Hartree-Fock method. These results are also shown to conform to the experimental data obtained for lighter ions of the Zn I isoelectronic sequence.     

The probabilities of radiative transitions and lifetimes of levels in the spectra of Cu XX,La IV

The probabilities of radiative electric dipole transitions 2p ⁵3p, 2p ⁶–2p ⁵3s, and 2p ⁵3d in the spectrum of neon-like copper Cu XX and 5p ⁵6p, 5p ⁶–5p ⁵6s, 5p ⁵7s, and 5p ⁵5d in the spectrum of xenon-like lanthanum La IV are calculated. The wave functions of the intermediate coupling were found from the wellknown experimental energy levels by the least-squares method (LSM). To transfer to an absolute scale the radial integrals for the transitions calculated in the form of a length on the Hartree–Fock functions have been used. By summing the calculated probabilities of the transitions, the lifetimes of the levels of configurations 2p ⁵3s, 2p ⁵3p, and 2p ⁵3d in the spectrum of Cu XX and levels of configurations 5p ⁵6s, 5p ⁵6p, and 5p ⁵7s in the spectrum of La IV have been obtained.     

Spectral and luminescence properties of gadolinium gallium garnet epitaxial films doped with terbium

Gadolinium gallium garnet single-crystal films containing terbium are grown through liquid-phase epitaxy from a supercooled solution melt in the PbO-B₂O₃ system. The optical absorption spectra in the wavelength range 0.2–10.0 μm and the luminescence spectra excited by synchrotron radiation with energies in the range 3.5–30.0 eV are investigated at temperatures of 10 and 300 K. It is revealed that the optical absorption spectra contain an absorption band with the maximum at a wavelength λ ≈0.260 μm, which corresponds to the spin-allowed electric dipole transition between the electronic configurations 4f ⁸(⁷ F ₆) → 4f ⁷(⁸ S)5d of the Tb³⁺ ions. The narrow low-intensity absorption bands attributed to the 4f → 4f transitions from the ⁷ F ₆ ground level to the ⁷ F _0–5 multiplet levels of the Tb³⁺ ions are observed in the wavelength range 1.7–10.0 μm. In the luminescence spectra measured at a temperature of 10 K, the highest intensity is observed for a band with the maximum at a wavelength λ ≈ 0.544 μm, which is associated with the ⁵ D ₄ → ⁷ F ₅ radiative transition in the Tb³⁺ ion.