A new joint analysis of the ground and first excited torsional states of methylformate

A global fit within experimental accuracy of microwave rotational transitions in the ground and first excited torsional states (v_t = 0 and 1) of methylformate (HCOOCH₃) is reported, which combines older measurements from the literature with new measurements from Kharkov. In this study the so-called ‘‘rho axis method’’ that treats simultaneously both A and E species of the ground and first excited torsional states is used. The final fit requires 55 parameters to achieve an overall unitless weighted standard deviation of 0.71 for a total of 10533 transitions (corresponding to 9298 measured lines) with rotational quantum numbers up to J ? 62 and K_a ? 26 in the ground state and J ? 35 and K_a ? 23 in the first excited torsional state. These results represent a significant improvement over past fitting attempts, providing for the first time a fit within experimental accuracy of both ground and first excited torsional states.     

The ground and first excited torsional states of methyl carbamate

A global fit within experimental accuracy of microwave and millimeter-wave transitions in the ground and first excited torsional states of methyl carbamate (H₂NC(O)OCH₃) is presented. The data set consisting of 995 v_t = 0 and 731 v_t = 1 transition frequencies combines 1544 new measurements from Kharkov with previously published v_t = 0 microwave lines. In this study the so-called “rho axis method” that treats simultaneously both A and E species of the ground and first excited torsional states is applied to the methyl carbamate data set for the first time. The final fit requires only 32 parameters to achieve a unitless weighted standard deviation for the whole fit of 0.89 for a total of 1726 transitions with rotational quantum numbers up to J ? 20 and K_a ? 10. The barrier to internal rotation of the methyl group obtained in this study, V₃ = 359.141(24) cm⁻¹, is in good agreement with previously published values but more accurate.     

Reinvestigation of the ground and first torsional state of methylformate

We have reinvestigated the laboratory spectrum for the methylformate HCOOCH₃ molecule involving both the ground and first excited torsional states.We have fitted within almost experimental accuracy a data set for this molecule consisting of 3496 v_t=0 and 774 v_t=1 microwave lines, using the so-called “rho axis method” (RAM) and a model extended to include perturbation terms through eighth order. The previously published microwave lines covering the J values up to 43 in the ground state and up to 18 in the first excited state have been extended by 434 new measurements from Lille in the 567–669 GHz spectral range, corresponding to transitions with J_max=62, K_max=22 in v_t=0. The final fit requires only 49 parameters to achieve a unitless weighted standard deviation of 1.43 for a total of 4270 lines for the whole fit. This result represents an improvement over the previous fit which achieved a standard deviation of 1.96 for 3862 lines using 69 parameters. A calculation of the line strengths of torsion–rotation transitions up to J = 60 needed for the astronomical survey is also provided.     

Microwave spectrum of trans 3-fluorophenol in excited torsional states

The microwave rotational spectra of the trans conformer of 3-fluorophenol have been observed in excited torsional states and analyzed in the frequency range 12.0-43.0 GHz using conventional microwave and Radio-Frequency Microwave Double Resonance (RFMWDR) techniques. Analysis of the ground torsional state spectrum has been extended to higher rotational states. Least-squares analysis of three sets of rotational transitions yield rotational and centrifugal distortion constants for the ground and first two excited torsional states. A nonlinear behavior of the variation of inertial defect with the torsional quantum number was observed.     

Rotational energy surface and quasiclassical analysis of the rotational energy level cluster formation in the ground vibrational state of PH3

We report and substantiate a method for constructing the rotational energy surface (RES) of a molecule as a pure classical object. For an arbitrary molecule we start from the potential energy surface rather than from a conventional “effective Hamiltonian”. The method is used for constructing the RES of the PH₃ molecule in its ground vibrational state. We have used an ab initio potential energy surface [D. Wang, Q. Shi, Q.-S. Zhu, J. Chem. Phys. 112 (2000) 9624-9631; S.N. Yurchenko, M. Carvajal, P. Jensen, F. Herregodts, T.R. Huet, Chem. Phys. 290 (2003) 59-67.]. The shape of the RES is shown not to change for J from 0 to 120. The procedure of quasiclassical quantization of the RES was also undertaken, yielding a set of quasiclassical critical values of the angular momentum. The results explain the structure of quantum rotational energy levels obtained by variational calculations [S.N. Yurchenko, W. Thiel, S. Patchkovskii, P. Jensen, Phys. Chem. Chem. Phys. 7 (2005) 573-582].     

Magnetic phase transitions in Nd7Rh3 single crystal

Magnetic phase transitions in rare earth intermetallic compound Nd₇Rh₃ have been investigated using a single crystal. Measurement results of magnetization, magnetic susceptibility, specific heat, and electrical resistivity reveal that Nd₇Rh₃ has two magnetic phase transitions at T_N=34 K, T_t2=9.1 K and a change of the magnetic feature at T_t1=6.8 K in the absence of an external magnetic field. Antiferromagnetic orderings exist in all the three magnetic states; a large magnetic anisotropy between the c-axis and the c-plane is observed. In the magnetic phase below T_t2, an irreversible field-induced magnetic phase transition takes place in the c-plane; after removing external magnetic field, a coexistence state of ferro- and antiferromagnetic ordering or a ferrimagnetic state having a remanent magnetization M_R is stabilized. The M_R decays to a certain value for several hours after the first process; a magnetic field cooling effect was also observed in the c-plane below T_t2. In the antiferromagentic state above T_t2, the irreversibility disappears and an ordinary antiferromagnetic state takes place. As the origin of this phenomenon, a kind of martensitic structural transition that is observed in Gd₅Ge₄ can be considered.     

Accurate rotational spectroscopy of sulfur dioxide, SO2, in its ground vibrational and first excited bending states, v2 = 0, 1, up to 2 THz

Approximately 150 pure rotational transitions each have been recorded for SO₂, v₂ = 0 and 1, in selected frequency regions up to 2 THz. The J and K_a quantum numbers reach very high values: 92 and 23, respectively, for the ground vibrational state and 81 and 21, respectively, for the first excited bending state. The highest levels accessed are almost 3000 cm⁻¹ above ground. The relative experimental uncertainties Δν/ν are about 10⁻⁸ for several medium to strong, isolated lines, and generally better than 2.5 × 10⁻⁷. Improved spectroscopic parameters have been obtained for both states, particularly for the excited bending state. In fact, the accuracies with which the energy levels of the v₂ = 1 state are known depend essentially only on the accuracy with which the vibrational spacing is known from infrared spectroscopy.     

Submillimeter spectrum of methyl bromide (CH3Br)

Methyl bromide is a ubiquitous component of the atmosphere, but has yet to be remotely detected in the upper atmosphere. Due to the strong ozone depletion capability of the activated bromine species, the total atmospheric bromine load needs to be carefully monitored. Combined analysis of precise measurements and cataloging of the rotational spectrum of methyl bromide may enable its concentration to be monitored with future remote sensing instrumentation. In an effort to extend and improve previous work for this molecule, the spectrum of CH₃Br has been measured at JPL. Using an isotopically enriched ¹³CH₃Br (90%) sample, spectra have been recorded from 750 to 1200 GHz. Quantum number assignments cover the CH₃⁷⁹Br, CH₃⁸¹Br, ¹³CH₃⁷⁹Br and ¹³CH₃⁸¹Br isotopologues with J < 66 and K < 17 for the ground and ν₃ vibrational states. The dataset for the ¹²C isotopologues is more precise than previous THz measurements resulting in reductions of rotational and distortion parameter uncertainties by factors of 2-15. Parameters of the ν₃ state of the ¹²C isotopologues are improved by 2-105. The spectra of the ¹³C isotopologues are the first reported beyond J = 2.     

Magnetic properties of Nd0.9Dy0.1Fe3(BO3)4

The magnetic properties of trigonal Nd_0.9Dy_0.1Fe₃(BO₃)₄ substituted compound with the competitive Nd-Fe and Dy-Fe exchange interactions have been investigated. It has been shown that in Nd_0.9Dy_0.1Fe₃(BO₃)₄ a spontaneous spin-reorientation transition from an ease-axis state to an easy-plane occurs near 8 K. Anomalies of the magnetization curves are observed in a spin-flop transition induced by the magnetic field B‖c. The calculations were performed using a molecular-field approximation and a crystal-field model for the rare-earth subsystem. Extensive experimental data on the magnetic properties of Nd_0.9Dy_0.1Fe₃(BO₃)₄ have been interpreted and good agreement between theory and experiment has been achieved using the obtained theoretical dependences.     

Ground state rotational spectrum of nitrogen trifluoride: The K = 3 splittings of NF3 and NF3

The ground state rotational spectrum of the ¹⁴NF₃ and ¹⁵NF₃ isotopic species of nitrogen fluoride has been observed in the ∼450-810 GHz frequency range. This investigation allowed us to improve the rotational parameters for both isotopologues. In particular, for the first time the K = 3 line splitting parameter and the sextic centrifugal distortion constants have been determined for ¹⁵NF₃.     

Ab initio calculation of electronic transition moments for singlet excited states of the H2 molecule

Ab initio CI electronic dipole transition moments have been calculated for the transitions between singlet states of the hydrogen molecule correlating asymptotically with H(nl)+H(1s) (n=1,2,3). The investigated singlet-singlet transitions include the 30 (n=3) inter-Rydberg transitions and the 32 transitions which may contribute to absorption in the far wings of the Balmer α line of atomic hydrogen perturbed by another hydrogen atom in its ground state. Results are presented for internuclear distances 1.0a₀?R?12a₀. The present results compare well with the previous theoretical calculations available for about half of the transitions treated in the present work. Thirty eight new transitions are presented. Adiabatic potential energies for the and and improved energies for the and states are reported as well.     

Oxygen vacancy in LiTiPO5 and LiTi2(PO4)3: A first-principles study

The structures of LiTiPO₅ and LiTi₂(PO₄)₃, as well as the possibility of oxygen vacancies formation in the systems are studied by first-principles calculations. It is found that oxygen vacancies can be formed in LiTiPO₅ and LiTi₂(PO₄)₃ under oxygen poor condition. The formation of oxygen vacancies introduce a defect band within their band gaps, which is expected to improve the electronic conductivity of LiTiPO₅ and LiTi₂(PO₄)₃ significantly. Meanwhile, a great concentration of oxygen vacancies may increase the discharge voltage of LiTiPO₅ and LiTi₂(PO₄)₃.     

Microwave dielectric properties of (1 − x)(Mg0.95Co0.05)TiO3–x(Na0.5La0.5)TiO3 ceramic system

The microstructures and the microwave dielectric properties of the (1 − x)(Mg_0.95Co_0.05)TiO₃–x(Na_0.5La_0.5)TiO₃ ceramic system were investigated. Two-phase system was confirmed by the XRD patterns and the EDX analysis. A co-existed second phase (Mg_0.95Co_0.05)Ti₂O₅ was also detected. The microwave dielectric properties are strongly related to the density and the matrix of the specimen. A new microwave dielectric material 0.88(Mg_0.95Co_0.05)TiO₃–0.12(Na_0.5La_0.5)TiO₃, possessing an excellent combination of dielectric properties: ε_r  22.36, Q × f  110,000 GHz (at 9 GHz), τ_f  2.9 ppm/°C), is proposed as a candidate dielectric for GPS patch antennas.     

High-resolution infrared spectra of HCF3 in the ν6 (500 cm) and 2ν6 (1000 cm) regions: rovibrational analysis and accurate determination of the ground state constants C0 and DK

The high-resolution infrared spectrum of HCF₃ was studied in the ν₆ fundamental (near 500 cm⁻¹) and in the 2ν₆ overtones (near 1000 cm⁻¹) regions. The present study reports on the analysis of the hot bands in the ν₆ region, as well as the first observation and assignment of the 2ν₆² perpendicular band. Using ν₆, 2ν₆^±2–ν₆^±1 and 2ν₆² experimental wavenumbers, accurate coefficients C₀ and D_K⁰ of the K-dependent ground-state energy terms were obtained, using the so-called “loop method.” Ground-state energy differences Δ(K,J)=E₀(K,J)−E₀(K−3,J) were obtained for K=3–30. A least-squares fit of 81 such differences gave the following results (in cm⁻¹): C₀=0.1892550(15); D_K⁰=2.779(26) × 10⁻⁷.     

High-resolution FTIR spectroscopy of the 3ν2 band of PH3

High-resolution Fourier transform spectrum of phosphine (PH₃) at room temperature has been recorded in the region of the 3ν₂ band (2730-3100 cm⁻¹) at an apodized resolution of 0.005 cm⁻¹. About 200 vibration-rotation transitions have been least squares fitted with an rms of 0.00039 cm⁻¹ after taking into account the ΔK = ±3 interaction.     

Rotational spectra of gauche perfluoro-n-butane, C4F10; perfluoro-iso-butane, (CF3)3CF; and tris(trifluoromethyl)methane, (CF3)3CH

The microwave spectra of the gauche conformer of perfluoro-n-butane, n-C₄F₁₀, of perfluoro-iso-butane, (CF₃)₃CF, and of tris(trifluoromethyl)methane, (CF₃)₃CH, have been observed and assigned. The rotational and centrifugal distortion constants for gauche n-C₄F₁₀ are: A = 1058.11750(7) MHz, B = 617.6832(1) MHz, C = 552.18794(1) MHz, Δ_J = 0.0257(5) kHz, δ_J = 0.0052(3) kHz. A C-C-C-C dihedral angle, ω, of ∼55° has been determined. These values agree well with those obtained from a coupled cluster (CCSD/cc-PVTZ) calculation. The rotational and centrifugal distortion constants for iso-C₄F₁₀ and iso-C₄HF₉ are: B_o = 816.4519(4) MHz, D_J = 0.023(2) kHz, and B_o = 903.6985(25) MHz, D_J = 0.043(4) kHz, respectively. The dipole moment of iso-C₄F₁₀ and iso-C₄HF₉ have been measured and found to be 0.0338(8) and 1.69(9) D, respectively.     

Soft-mode driven tetragonal-to-monoclinic phase transition in multiferroic BiFeO3

The phase transition of BiFeO₃ (BFO) from tetragonal to monoclinic induced by pressure was investigated by first-principles method. The sequential monoclinic phase, _Ma$M_{\mathrm{a}}$, which is favorable during low compression with respect to the tetragonal phase, was characterized. The order parameters were calculated in the vicinity of the phase transition, showing that phase transition has a second-order character. The results demonstrated that the pressure-induced tetragonal-to-monoclinic phase transition in BFO is related to the softening behavior of the E mode, which are very helpful in further investigations of the morphotropic phase boundary (MPB) in lead-free materials.     

中子探测晶体Li6Gd(BO3)3:Ce的光谱特性研究

文章用提拉法生长出Li₆Gd(BO₃)₃:Ce晶体,并对其光谱性能与发光过程进行了探索. 借助于真空紫外-紫外透过光谱测试,发现晶体的透过光谱中存在Ce³⁺离子和Gd³⁺的特征吸收峰,同时还存在与Ce⁴⁺离子相关的电荷迁移带. 对晶体的真空紫外-紫外激发发射光谱进行研究发现,在晶体存在着Ce³⁺离子的5d→4f辐射跃迁发光与Gd³⁺离子的4f→4f辐射跃迁发光,而且存在着Gd³⁺→Ce³⁺之间的能量传递. 对Li₆Gd(BO₃)₃:Ce晶体的X射线与γ射线激发发射光谱研究可知,晶体在高能射线激发下的闪烁光主要是Ce³⁺离子的发光. 关键词： 6Gd(BO₃)₃:Ce晶体')" href="#">Li₆Gd(BO₃)₃:Ce晶体 真空紫外-紫外透过光谱 真空紫外-紫外激发发射光谱 能量传递     

Synthesis and ion conductivity of (Bi2O3)0.75(Dy2O3)0.25 ceramics with grain sizes from the nano to the micro scale

Using (Bi₂O₃)_0.75(Dy₂O₃)_0.25 nano-powder synthesized by reverse titration co-precipitation method as raw material, dense ceramics were sintered by both Spark Plasma Sintering (SPS) and pressureless sintering. According to the predominance area diagram of Bi-O binary system, the sintering conditions under SPS were optimized. (Bi₂O₃)_0.75(Dy₂O₃)_0.25 ceramics with relative density higher than 95% and an average grain size of 20 nm were sintered in only 10 min up to 500 °C. During the pressureless sintering process, the grain growth behavior of (Bi₂O₃)_0.75(Dy₂O₃)_0.25 followed a parabolic trend, expressed as D² − D₀² = Kt, and the apparent activation energy of grain growth was found to be 284 kJ mol^− 1. Dense (Bi₂O₃)_0.75(Dy₂O₃)_0.25 ceramics with different grain sizes were obtained, and the effect of grain size on ion conductivity was investigated by impedance spectroscopy. It was shown that the total ion conductivity was not affected by the grain size down to 100 nm, however lower conductivity was measured for the sample with the smallest grain size (20 nm). But, although only the δ phase was evidenced by X-ray diffraction for this sample, a closer inspection by Raman spectroscopy revealed traces of α-Bi₂O₃.     

A comparative study of electronic structure and magnetic properties of SrCrO3 and SrMoO3

A comparative study of electronic structure and magnetic properties of SrCrO₃ and SrMoO₃ has been carried out using FPLAPW method with density-functional theory. The calculated results suggest that both compounds are nonmagnetic (NM) metal in cubic structures at room temperature, and they exhibit very similar band structure and electronic properties except more extend Mo 4d orbitals than Cr 3d electronic states. However, the electronic structure and magnetic properties exhibit remarkable differences between them in the low temperature phases. SrCrO₃ is with a C-AFM ground state with magnetic moment of 1.18μ_B/Cr in the tetragonal structure, while SrMoO₃ is with a NM ground state in the orthorhombic structure. It is assumed that the extend 4d orbitals may be the reason which results in NM solution at low temperature phase of SrMoO₃.