Microwave spectra and internal rotation in α-angelicalactone

The rotational spectrum of α-angelicalactone has been analyzed in the frequency range 18.0–40.0 GHz. The internal rotation barrier of the methyl group has been determined in the ground and four vibrationally excited states from the A-E splittings. The results indicate a possible rotational between the methyl torsion and the ring puckering mode. The ground state rotational parameters are consistent with a planar ring skeleton. The dipole moment components obtained from Stark displacements are μ_a = 3.16(1) D and μ_b = 2.59(2) D with a total value of 4.08(2) D.     

Davydov doublets in Raman spectra of ϵ-GaSe

Raman scattering spectra of ϵ-GaSe and β-Gas crystals were examined at temperature 8° and 295°K with a resolution of 0.7 cm⁻¹. At low temperature the Davydov splitting of modes in ϵ-GaSe could be accurately measured. The largest splitting of the Raman bands in ϵ-GaSe was found to be about 3 cm⁻¹ and correlates well with that predicted from a model based on the molecular nature of this compound.     

Heavy-flavour spectra in high-energy nucleus–nucleus collisions

The propagation of the heavy quarks produced in relativistic nucleus–nucleus collisions at RHIC and LHC is studied within the framework of Langevin dynamics in the background of an expanding deconfined medium described by ideal and viscous hydrodynamics. The transport coefficients entering into the relativistic Langevin equation are evaluated by matching the hard-thermal-loop result for soft collisions with a perturbative QCD calculation for hard scatterings. The heavy-quark spectra thus obtained are employed to compute the differential cross sections, the nuclear modification factors R _AA and the elliptic-flow coefficients v ₂ of electrons from heavy-flavor decay.     

Ghost lines in Mössbauer relaxation spectra

The appearance in Mössbauer relaxation spectra of ghost lines, which are narrow lines that do not correspond to transitions between real hyperfine energy levels of the resonant system, is examined. It is shown that in many cases of interest, the appearance of these ghost lines can be interpreted in terms of the relaxational averaging of one or more of the static interactions of the ion.     

Recurrence spectra of Li atom in strong external fields

Based upon our previous work [Commun. Theor. Phys.. 40,702 (2003)], we developed the closed orbit theory from two degrees of freedom to three non-separable degrees of freedom and calculated the recurrence spectra of Li Rydberg atom in strong perpendicular electric and magnetic fields. The Fourier transformed spectra of Li atom has allowed direct comparison between the resonance peaks and the scaled action values of closed orbits, whereas the nonhydrogenic resonance can be explained in terms of the new orbits created by the core scattering. The semiclassical result is in good agreement with the quantum one, which suggests that our calculation is correct.     

Radiofrequency mössbauer forward scattering spectra in magnetic materials

Radiofrequency (RF) Mössbauer spectra in experiments on forward scattering by thick samples of iron borate (FeBO₃) below the Neel temperature are measured. The spectra have satellites spaced by doubled RF-field frequency. A semiclassical model of Mössbauer transmission through a magnetic absorber exposed to RF reversals of a hyperfine field on nuclei is proposed. The model reproduces all features of the measured spectra. Experiments and modeling calculations indicate additional possibilities for studying soft magnetic materials using this measurement scheme.     

Quantum spectra and classical periodic orbit in the cubic billiard

Quantum billiards have attracted much interest in many fields. People have made a lot of researches on the two-dimensional (2D) billiard systems. Contrary to the 2D billiard, due to the complication of its classical periodic orbits, no one has studied the correspondence between the quantum spectra and the classical orbits of the three-dimensional (3D) billiards. Taking the cubic billiard as an example, using the periodic orbit theory, we find the periodic orbit of the cubic billiard and study the correspondence between the quantum spectra and the length of the classical orbits in 3D system. The Fourier transformed spectrum of this system has allowed direct comparison between peaks in such plot and the length of the periodic orbits, which verifies the correctness of the periodic orbit theory. This is another example showing that semiclassical method provides a bridge between quantum and classical mechanics.     

Single-pulse CARS spectra in solid propellant combustion at atmosphere pressure

The unstable-resonator spatially enhanced detection (USED) coherent anti-stokes Raman spectroscopy (CARS) measurements of temperature and N2 concentration in the combustion of solid propellant at atmosphere pressure are reported. The USED CARS measurement system has a high spatial solution of ~ 0.1 mm in diameter and 3 mm in length, and permits instantaneous measurement at 10-Hz rate. The single-pulse N2 Q-branch CARS spectra have been obtained from the propellant combustion. The temperatures and N2 concentrations of the propellant flame at different height have been achieved by fitting the experimental data to theoretical spectra. The results indicate that the temperature is up to ~ 2500 K with N2 concentration in a range from 10% to 26%.     

Splitting of Vavilov-Čerenkov radiation spectra in excited dispersing media

Within the framework of quantum electrodynamics, the additional mechanism of shaping Vavilov-erenkov radiation, characteristic for excited media and not described by their refractive index, is examined. Its interference with the usual generation channel under stationary homogeneous conditions can eliminate the spectrum splitting detected earlier theoretically. Splitting is restored in inhomogeneous situations. The time inhomogeneity is analyzed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 14–19, July, 1988.     

Interference effects in Mössbauer spectra of E2 transitions

It is shown that interference effects in Mössbauer transmission experiments with pure E2 and mixed E2/M1 transitions are, generally, due to interference between the internal conversion and the photoeffect. This interference effect is mainly determined by the quadrupole part of the photoabsorption, which is comparable to the dipole part at transition energies of about 100 keV. A noticeable part of the interference effect in the case of E2 transitions can be attributed to the interference between the nuclear resonant scattering and Rayleigh scattering on atomic electrons. The angular distribution of the (, e) reaction cross section has been calculated for E2 transitions.     

Optogalvanic spectra of calcium in the 6090–6760 Å region

Optogalvanic spectra of some 30 transitions of calcium originating from the ground state as well as from several excited states (4s4p ^1,3P, 4s3d ^1,3D, 4s5p ³P, 3d4p ³D, ³F) have been investigated using laser-irradiation of a low-current glow discharge in a thermionic diode. The influence of various experimental parameters such as bias field, oven temperature and buffer gas pressure on the spectra are reported. Seven previously unreported transitions are recorded including four forbidden transitions which violate the J selection rules. An interesting anomaly observed in the non-statistical population of the 4s3d ³D_3,2,1 multiplet is discussed where the populations of ³D₃:³D₂:³D₁ are in the ratio of 94:5:1. A possible explanation is based on avoided crossing between potential energy curves of the Ca-Ar molecule.     

Muon decay in orbit spectra for μ???e conversion experiments

In mixed-valence manganites, the doped iron species play the roles of simultaneous probes and ruiners for the orbital order occurring in the Mn-O electronic subsystem. We investigated the Mn^3?+?-based undoped system RBaMn₂O_5.5 and the half-doped systems RBaMn₂O₆, and RBaMn₂O₅ substituting a tiny portion of Mn^3?+? sites with Fe^3?+?. Single-site M?ssbauer spectra were observed at room temperature in the charge-orbitally ordered state, i.e., below T_COO, for R=Y, Sm, Gd. Size of the rare earth ion strongly influences the quadrupole splitting in RBaMn₂O₆, but not in RBaMn₂O₅.     

High resolution spectra of the red fluorescence in chemical oxygen-iodine laser

In our chemical oxygen-iodine laser(COIL)experiments we accidentally ob-served relatively strong red fluorescence while setting a hot metal wire in the cavity.The in-tensity of such emission is 2～3 orders of magnitude stronger than the initial O_2(~1A)dimerfluorescence.The fluorescence spectrum was measured with OMA and Bomem FT spectrome-ter respectively and the highest resolution of the measurement is 0.1cm~(-1).The emission maycome from O_4 molecules or an isomer of Cl_2O_2.     

Shift of relaxation-stimulated resonances in Mössbauer absortion spectra in a static magnetic field

New features are obtained for previously predicted relaxation-stimulated resonances in Mössbauer spectra of nanomagnets exposed to an external rf field: the resonances should undergo low-frequency shift upon applying a weak static magnetic field. Analytic expressions for the resonance frequencies as functions of the static field are obtained within a simplified relaxation model. This effect extends the possibilities for experimental observation of the predicted effects, because tuning to the resonance may be accomplished not only by changing frequency of the rf field but also by varying the amplitude of the alternating field and the strength of the static field.     

Magnetic “doublets” in Mössbauer spectra of superparamagnetic particles

It is shown that the Mössbauer magnetic hfs spectra of a superparamagnetic particle are cardinally affected by the rotation of its magnetic moment about the magnetic anisotropy field. This rotation renormalizes the nuclear g factors and qualitatively transforms the spectra. In particular, apart from the well-known magnetic sextet, five, four, three, and even two (magnetic “doublet”) lines can arise in the ⁵⁷Fe absorption spectra.     

Superconductivity in boron carbide? Clarification by low-temperature MIR/FIR spectra

The electronic structure and phonon density of B(13)B(2) boron carbide calculated by Calandra et al (2004 Phys. Rev. B 69 224505) defines this compound as metallic, and the authors predict superconductivity with T(C)s up to 36.7 K. Their results are affected by the same deficiencies as former band structure calculations on boron carbides based on hypothetical crystal structures deviating significantly from the real ones. We present optical mid IR/far IR (MIR/FIR) spectra of boron carbide with compositions between B(4.3)C and B(10.37)C, evidencing semiconducting behaviour at least down to 30 K. There is no indication of superconductivity. The spectra yield new information on numerous localized gap states close to the valence band edge.     

Detected line shape distortions in mössbauer spectra of beryllium alloys

Mössbauer spectra of the solid solutions and iron-containing phases that precipitate upon isothermal annealing in beryllium-based alloys with different impurity concentrations are obtained and fitted using the equation of convolution of three Lorentz lines. The possibility of performing a consistent analysis of decomposition of the solid solution using the Avrami classification and precipitation of the secondary phases based on diffusion growth models is demonstrated.     

Macroscopic quantum effects observed in Mössbauer spectra of antiferromagnetic nanoparticles

The ⁵⁷Fe Mössbauer spectra of antiferromagnetic nanoparticles have been measured for almost half a century and often displayed a specific (non-superparamagnetic) temperature evolution of the spectral shape which looks like a quantum superposition of well-resolved magnetic hyperfine structure and single line or quadrupolar doublet of lines with the temperature-dependent partial spectral areas. We have developed a quantum-mechanical model for describing thermodynamic characteristics of an ensemble of ideal and “uncompensated” antiferromagnetic nanoparticles with uniaxial magnetic anisotropy in the first approximation of slowly relaxing macrospins of magnetic sublattices. This model allows one to qualitatively describe the macroscopic quantum effects observed in the Mössbauer spectra and to clarify principally the difference in thermodynamic properties of ferromagnetic and antiferromagnetic particles revealed in spectroscopic measurements.     

Emission spectra of a (?)-type three-level atom in a Kerr medium

We investigate the emission spectra of a (?)-type three-level atom interacting with a single-mode optical field in an ideal cavity filled with a Kerr medium and discuss the structure of emission spectrum when the optical field is initially in a pure number state and a coherent state, respectively. It is shown that the structure of emission spectrum depends not only on the photon number distribution, but also on the strength of incident field and the coupling of Kerr medium to the field.     

Polarization spectra of Rb atoms and their application in laser frequency stabilization

Polarization spectra of rubidium atoms were investigated with different uncrossed angles between the polarizer and the analyzer. The variation of the spectra was derived theoretically as a function of arbitrary angle, and measured experimentally for different angles. The spectral profile of D2 line of rubidium was further used to stabilize the frequency of a diode laser. It was demonstrated that the laser linewidth was reduced to 2 MHz.