Analysis of 2ν2, ν1, and ν3 of H2Se

We have run the high-resolution infrared absorption spectrum of 2ν₂, ν₁, and ν₃ of H₂Se in the region 5.2 to 3.8 μm. We have identified and fitted approximately 520 transitions in 2ν₂, 930 transitions in ν₁, and 620 transitions in ν₃. Included are transitions from the isotopic species containing selenium isotopes 82, 80, 78, 77, and 76. Using Typke's rotational Hamiltonian, we analyzed all isotopic species simultaneously. Ground-state constants were determined from a simultaneous least-squares fit of 879 distinct ground-state combination differences formed from our data and 109 microwave transitions. Upper-state constants were obtained from least-squares fits of our spectral lines analyzing 2ν₂ as a single noninteracting band and analyzing the Coriolis interacting bands ν₁ and ν₃ simultaneously, keeping the ground-state constants fixed.     

Identification of forbidden vibration-rotation transitions in 15NH3

Forbidden Δ|k ? l| = 3 vibration-rotation transitions have been observed in the ν₄ band of ¹⁵NH₃. The analysis of these transitions, together with previously published data on the allowed transitions, has made it possible to determine a set of molecular parameters, including for the first time the rotational constant C as well as the centrifugal distortion constants D_K and H_KKK, which are necessary for the calculation of energy levels. Some weak forbidden transitions in the ν₂ band have also been observed.     

Some exact results for the spin-1/2 Falicov-Kimball model in the strong coupling limit

The spin-1/2 Falicov-Kimball model for electronically driven valence and metal-insulator transitions is studied analytically using strong-coupling perturbation theory. It is shown that in the limit of the infinite interaction strength between localized and itinerant electrons the Falicov-Kimball model undergoes two types of discontinuous valence transitions: the insulator-metal transitions from an integer-valence ground state (n _f = 1) into an inhomogeneous intermediate-valence ground state (0 < n _f < 1) and the insulator-metal transitions from n _f = 1 to n _f = 0. In addition, we discuss the role of the electron-phonon interaction on the mechanism of valence transitions and we present possible extensions of the exact one dimensional results to higher dimensions.     

Infrared spectrum of hydrogen in the condensed phase with high-sensitivity spectrometers: Experiments with a 0.04-cm−1 Fourier transform spectrometer in the range 1.5–12 μm

The infrared spectrum of solid and liquid hydrogen was recorded using a Fourier spectrometer. The pure rotational U transitions, U₀(0) in solid para hydrogen and U₀(1) in solid normal hydrogen, with the accompanying phonon branches were observed for the first time. In addition, the rotational double transitions S₀(0) + S₀(1) and S₀(1) + S₀(1) were identified. The identifications of these transitions are based on positions calculated by making use of gas phase molecular constants. In the liquid the double transitions are preserved but the single transitions U₀(0) and U₀(1) are entirely absent. The region of Q_1←0(J) reveals structure which has not been reported before. Its interpretation is presented.     

High resolution spectrum of the ν5 band of nitric acid (HNO3) near 880 cm−1

Tunable diode lasers have been used to measure the spectrum of HNO₃ from 853 to 892 cm^?1. A Fermi interaction with the nearby 2ν₉ state perturbs some of the transitions and causes some problems in the analysis, but several hundred lines have been assigned and fit to a set of band constants with a standard deviation of 0.0007 cm^?1. The measurements include most of the P branch, the strongest lines of the Q branch, and some R-branch transitions. Only A-type transitions have been identified and any B-type transitions must be much weaker.     

Radiofrequency spectroscopy of AsH3 inside a CO2N2O laser cavity

The method of radiofrequency spectroscopy inside a CO₂N₂O laser cavity has been applied to the observation of pure nuclear quadrupole resonance, A₁-A₂ transitions and two-photon transitions of AsH₃. From the assignment of these transitions some coincidences between laser lines and Δk = 3 transitions in the ν₂ band and Δ|k ? l|; = 3 transitions in the ν₄ band have been assigned. The quadrupole coupling constant eqQ and its rotational dependence χ_J, χ_K and χ_d, and the spin-rotation constants C_N and C_K for the As nucleus have been determined for the ground state. The effective values of eqQ has been determined for the ν₂ and the ν₄ states.     

A new type of second-order phase transition derived from Devonshire's theory of ferroelectrics

Including external fields Devonshire's theory of ferroelectric phase transitions leads to a type of second-order transitions for which the order parameter is different from zero below and aboveT _c . Although in a certain limiting case the order parameter becomes zero aboveT _c the resulting theory is nevertheless different from the usual Landau-theory suggesting the existence of different types of systems undergoing second-order phase transitions.     

10-μm sub-doppler laser-Stark spectroscopy of methyl chloride: Analysis of the ν6 bands of the CH335Cl and CH337Cl

About 900 Stark transitions from 70 vibration-rotation transitions in CH₃³⁵Cl and about 400 transitions from 38 transitions in CH₃³⁵Cl in the ν₆ band have been assigned. These data were analyzed simultaneously with previously published microwave data on the ν₆ = 1 state. The fit has a standard deviation of about 2 MHz for the data for both isotopes. The isoptopic shift ν₆35 ? ν₆37 = 0.3766(6) cm^?1. Rotational dependence of the dipole moment was also just apparent at about μ_J = μ_K = 1 × 10^?5 D, and a complete set of molecular constants is given.     

SU (2N f) ⊗ O(3) light diquark symmetry and current-induced heavy baryon transition form factors

We study the current-induced bottom baryon to charm baryon transitions in the Heavy Quark Symmetry limit as m_q → ∞. Our discussion involves s-wave to s-wave as well as s-wave to p-wave transitions. Using a constituent quark model picture for the light diquark system with an underlying SU (2N_f) ? O(3) symmetry and the heavy quark symmetry we arrive at a number of new predictions for the reduced form factors that describe these transitions.     

Microwave spectrum of the vibrational excited states ν6 and ν8 of formic acid: Contribution to the assignment of the Formic Acid Submillimeter Laser

The microwave spectrum of the ν₆ and ν₈ vibrationally excited states of H¹²COOH has been reinvestigated in the 10–200-GHz region, and 23 new transitions, essentially of the b type, were measured. The transitions allowed us to obtain a set of improved parameters for each of these two states which contribute to the assignment of the Formic Acid Submillimeter Laser. The vibrational energies of the ν₆ and ν₈ states have been derived from the assignment of infrared pump transitions and the corresponding submillimeter transition of the optically pumped submillimeter laser.     

High pressure phase transition in super-cell LiBH4: An ab initio prediction

LiBH₄ which have attracted considerable attention from researchers due to the crystal structure characteristics is a metal hydride that can bind four hydrogen atoms. LiBH₄ which has high gravimetric and volumetric hydrogen density shows phase transitions at high pressures. In this regard, we created and analyzed LiBH₄ structure based on the first principles calculations, and then obtained the super-cell LiBH₄ structure. We achieved the phase transitions up to 20 GPa pressure with 2 GPa regular intervals for the super-cell LiBH₄. We observed the Pnma to Pnma*, Pnma* to P2₁/c, and P2₁/c to C2/c phase transitions and calculated the volume contractions accompanying these phase transitions. According to the obtained volumetric values, one can conclude that LiBH₄ can minimize the volumetric requirements of the hydrogen storage for systems that can be used at high pressures. Thus, the hydrogen storage capacity of LiBH₄ may increase at particular phases.     

Study of the ν3 and 2ν3 ← ν3 bands of 12CH3F by infrared laser sideband and submillimeter-wave spectroscopy

An infrared laser sideband spectrometer operating in the CO₂ laser region with 8- to 18-GHz sidebands has been used to record 266 transitions in the ν₃ band and 84 transitions in the 2ν₃ ← ν₃ band of ¹²CH₃F. The accuracy of the measured frequencies is estimated to be 1–3 MHz. A millimeter/submillimeter-wave spectrometer has been used to record the spectra of 48 pure rotational transitions in the ground vibrational state and 55 transitions in the v₃ = 1 vibrational state with an accuracy of 20–90 kHz. The new measurements have been combined with previous radio frequency and infrared laser results to derive sets of constants for the ground, v₃ = 1, and v₃ = 2 states for this molecule. Tables of the vibrational dependence of the parameters and of the near coincidences of the ν₃ and 2ν₃ ← ν₃ band transitions with CO₂ laser frequencies are given.     

Resonance structure of strength functions for first-forbidden β +/EC transitions

Experimental data obtained by measuring the fine structure of the strength function S _?? (E) in spherical and deformed nuclei were analyzed. The use of modern nuclear-spectroscopy methods made it possible to reveal the nuclear-deformation-induced splitting of peaks in S _?? (E) for transitions of the Gamow-Teller type. For first-forbidden transitions, the resonance nature of S _?? (E) was proven experimentally both for spherical and for deformed nuclei. It is shown that, at some values of the excitation energy, the intensity of first-forbidden transitions in nuclei can be commensurate with the intensity of Gamow-Teller transitions.     

Resonant polaron coupling of the n = 1 Landau level and the 2p+ donor state in GaAs

The n = 0 → > n = 1 Landau level and 1s ?2p⁺ impurity transitions in GaAs were investigated up to energies above the optical phonon energy ?Ω_LO and d.c. magnetic fields up to 25 T. Pinning of both transitions to an energy slightly above and below ?Ω_LO was observed. At an energy very close to ?Ω_LO two additional impurity transitions are found. These features are attributed to the resonant polaron effect which leads to hybridization and dipole selection rule breakdown. Also the spin doublet splitting of both transitions were resolved showing a strong magnetic field dependence which can not be explained by nonparabolicity of the conduction band alone.     

The Δk = ±2 perturbation-allowed ν4 band and inversion-rotation energy levels of 15NH3

More than 800 Δk = ±2 and 60 Δk = ±3 forbidden transitions to the ν₄ and 2ν₂ vibrational levels, respectively, have been assigned in the Fourier transform spectra of ¹⁵NH₃, recorded with a pathlength of 96 m. Combination differences derived from these transitions provide information on the spacing between the ground state energy levels with different rotational quantum numbers K in the interval from 0 to 16. These data along with wavenumbers of all the available allowed transitions pertaining to the ground and ν₂ states have been subjected to a simultaneous least-squares analysis using two different parametrization models to obtain precise values of the inversion-rotation energy levels.     

Anomalies of magnetoelastic properties and insulator-metal phase transitions induced by a magnetic field in substituted praseodymium manganites

The magnetostriction of Pr_0.6Ca_0.4MnO₃ and Pr_0.65Ca_0.28Sr_0.07MnO₃ manganite crystals is investigated in pulsed magnetic fields up to 250 kOe. The field-induced phase transitions from the charge-ordered antiferromagnetic (paramagnetic) state to the metallic ferromagnetic state are studied. It is found that these transitions are accompanied by abrupt negative jumps in the longitudinal and transverse magnetostrictions and a strong hysteresis at low temperatures. The threshold fields of transitions are determined, and the H-T phase diagrams are constructed.     

A phenomenological theory of possible sequences of ferrotoroidal phase transitions in boracites

A phenomenological theory of the sequence of two second-order phase transitions with close temperatures is considered; such transitions occur in the Ni-Br boracite. The thermodynamic potential is written as a function of polarization P _i, magnetization M _i, and toroidal moment T _i vectors and fields E _i and H _i; T _i is treated as an order parameter. It is assumed that only one coefficient of T _i ² passes through zero as T decreases. The possibility of a sequence of two proper ferrotoroidal phase transitions along the T ₁ and T ₂ components is demonstrated. Spontaneous T _i, P _i, and M _i vector values and equations for susceptibility tensors (dielectric χ _ij = dP _i/dE _j, magnetic k _ij = dM _i/dH _j, and magnetoelectric α_ij = dP _i/dH _j = dM _j/dE _i) were obtained for three phases. Some of these values have well-defined anomalies in the vicinity of transitions. All possible sequences of ferrotoroidal phase transitions in boracites are considered. Depending on two potential coefficient values, these sequences may consist of one, two, or three such transitions.     

SU(2N f) ⊗O(3) light diquark symmetry and current-induced heavy baryon transition form factors

We study the current-induced bottom baryon to charm baryon transitions in the Heavy Quark Symmetry limit asm _q→∞. Our discussion involvess-wave tos-wave as well ass-wave top-wave transitions. Using a constituent quark model picture for the light diquark system with an underlyingSU(2N _f)?O(3) symmetry and the heavy quark symmetry we arrive at a number of new predictions for the reduced form factors that describe these transitions.     

1-Butyne microwave spectrum,barrier to internal rotation,and molecular dipole moment

Measurements of rotational transitions of 1-butyne have been made in the range of ～20–130 GHz. Both a-type transitions up to J = 46 and b-type transitions up to J = 42 have been measured and fitted to a rotational Hamiltonian which includes centrifugal distortion terms. In addition to the five quartic centrifugal distortion constants, three sextic coefficients had to be included to reproduce the observed frequencies to within experimental error. The results of the analysis are sufficient for the prediction of all strong transitions throughout the millimeterwave range. A barrier to internal rotation of the methyl group of 3.260 kcal/mole (1 kcal/mole = 4.18 kJ/mole) has been derived from the first excited torsional state. Analysis of the second-order Stark effect has led to an accurate determination of both μ_a and μ_b with μ_a = 0.763(3) D and μ_b = 0.170(4) D.     

Microwave spectroscopy of propynal in the v2 = 1 vibrational state by IR-MW triple resonance

Infrared-microwave triple resonance was applied to microwave spectroscopy of propynal, HCCCHO, in the v₂ = 1 vibrational state. Eleven microwave transitions were newly observed by using a Zeeman-tuned 3.51 μm HeXe laser as the infrared radiation source. The spectrum was analyzed including the 11 transitions previously observed by double resonance. A least-squares fit of the 13 low-J transitions revealed that the rotational constants in the K_?1 = 1 states were slightly different from those of the K_?1 = 0 states. A higher-order rotational resonance was proposed for explanation of the effect.