Measurement of Δ1J(199Hg, 31P) in [HgPCy3(OAc)2]2 and relativistic ZORA DFT investigations of mercury–phosphorus coupling tensors

Using ³¹P solid-state NMR spectroscopy, anisotropy in the indirect ¹⁹⁹Hg-³¹P spin–spin coupling tensor (ΔJ) for powdered [HgPCy₃(OAc)₂]₂ (1) has been measured as 4700±300 Hz. Zeroth-order regular approximation (ZORA) density functional theory (DFT) calculations, including scalar and spin-orbit relativistic effects, performed on 1 and a series of other related compounds show that ΔJ(¹⁹⁹Hg, ³¹P) arises entirely from the ZORA Fermi-contact–spin-dipolar cross term. The calculations validate assumptions made in the spectral analysis of 1 and in previous determinations of ΔJ in powder samples, namely that J is axially symmetric and shares its principal axis system with the direct dipolar coupling tensor (D). Agreement between experiment and theory for various ¹⁹⁹Hg, ³¹P spin–spin coupling anisotropies is reasonable; however, experimental values of ¹J(¹⁹⁹Hg, ³¹P)_iso are significantly underestimated by the calculations. The most important improvements in the agreement were obtained as a result of including more of the crystal lattice in the model used for the calculations, e.g., a change of 43% was noted for ¹J(¹⁹⁹Hg, ³¹P)_iso in [HgPPh₃(NO₃)₂]₂ depending on whether the two or three nearest nitrate ions are included in the model. Finally, we have written a computer program to simulate the effects of non-axial symmetry in J and of non-coincidence of the J and D on powder NMR spectra. Simulations clearly show that both of these effects have a pronounced impact on the ³¹P NMR spectrum of ¹⁹⁹Hg–³¹P spin pairs, suggesting that the effects should be observable experimentally if a suitable compound can be identified.     

The diode laser spectrum of the ν2 band of 14ND3 and 15ND3

The spectra of the ν₂ bands of ¹⁴ND₃ and ¹⁵ND₃ were measured under Doppler-limited resolution with a diode laser spectrometer in order to resolve the K structure of the sR(J, K) and aR(J, K) multiplets. By a simultaneous least-squares analysis of these data, the Fourier spectra of the ν₂ band measured by Jones [J. Mol. Spectrosc.74, 409 (1979)], and the ground-state microwave transitions, sets of improved ν₂-band parameters were obtained, including the sextic centrifugal distortion coefficients.     

Spinon excitation spectra of the J1-J2 chain from analytical calculations in the dimer basis and exact diagonalization

The excitation spectrum of the frustrated spin-1/2 Heisenberg chain is reexamined using variational and exact diagonalization calculations. We show that the overlap matrix of the short-range resonating valence bond states basis can be inverted which yields tractable equations for single and two spinons excitations. Older results are recovered and new ones, such as the bond-state dispersion relation and its size with momentum at the Majumdar-Ghosh point are found. In particular, this approach yields a gap opening at J ₂ = 0.25J ₁ and an onset of incommensurability in the dispersion relation at J ₂ = 9/17J ₁ as in [S. Brehmer et al., J. Phys.: Condens. Matter 10, 1103 (1998)]. These analytical results provide a good support for the understanding of exact diagonalization spectra, assuming an independent spinons picture.     

On some low-temperature properties of (La, Ce)B6 alloys

Some recent experimental data on the magnetic susceptibility and the low-temperature magnetization of the (La, Ce)B₆ system are discussed in the light of the theoretical results. A value of the s-f exchange constant J is estimated which is also consistent with the results obtained from both the Kondo effect and the RKKY interaction.     

The microwave spectrum of the pyramidal isomer of disulfur difluoride: SSF2

The pyramidal isomer of disulfur difluoride, SSF₂, has been prepared by passing gaseous disulfur dichloride through heated potassium fluoride. The microwave spectra of three isotopic species of SSF₂ have been measured in the 26- to 76-GHz frequency region. For the most abundant isotopic species transitions with J values up to 79 have been observed. These data have been combined with previous measurements of low-J lines by R. L. Kuczkowski [J. Amer. Chem. Soc. 86, 3617–3621 (1964)] and fit to obtain values for the rotational constants and centrifugal distortion constants. The quartic centrifugal distortion constants have been used together with existing vibrational data to determine an harmonic force field for the molecule. Finally, ground state average and equilibrium structures have been calculated for SSF₂.     

Reduction of the effective rotational Hamiltonian for pyramidal XY3 molecules with a large-amplitude inversion motion

The previously described reduction of the effective rotational Hamiltonian for semirigid molecules of C_3v or D₃ point group symmetry [M. R. Aliev and V. T. Aleksanyan, Opt. Spectrosc.24, 201–206 (1968)] has been extended to nonrigid molecules with a significant inversion splitting of the energy levels (e.g., NH₃, H₃O⁺, CH₃^?, or SiH₃ molecules). Although for semirigid molecules like PH₃ or AsH₃, the parameters α and η′₃ which appear in the terms α[J₊³ + J_?³, J_z]₊ and η′₃(J₊⁶ + J_?⁶) are almost completely correlated, the effects of the inversion splitting and the accidental resonance which can occur between the interacting rotational levels in nonrigid molecules make it possible to determine α and η′₃ separately. The results of fitting the experimental data for ¹⁴NH₃ and ¹⁵NH₃ [?. Urban, Romola D'Cunha, K. Narahari Rao, and D. Papou?ek, Canad. J. Phys.62, 1775–1791 (1984); Romola D'Cunha, ?. Urban, K. Narahari Rao, L. Henry, and A. Valentin, J. Mol. Spectrosc.111, 352–360 (1985)] are in agreement with this conclusion. The possibility of the determination of the sign of η₃ from a simultaneous analysis of the allowed and Δk = ±3 forbidden transitions in semirigid XY₃ molecules has been discussed.     

Luminescence and crystal-field fitting of two optical isomeric complexes of europium

FT-IR and Raman vibrational spectra and electronic emission spectra have been recorded for enantiomers of europium complexes with DBM: dibenzoylmethanate 1,2, and TTFA: 2-thenoyltrifluoroacetonate 3,4, employing the chiral ligands L_SS(+)- and L_RR(-)-4,5-pinene bipyridine. Contrary to the previously published X-ray data, where geometrical differences were stated to occur for particular enantiomers, the vibrational (and the emission) spectra of the individual optical isomers of a complex are not distinguishable. Using excitation into the Eu³⁺⁵D₂ multiplet term, the emission intensity is weak from ⁵D₁, whereas a complex structure is observed for the ⁵D₀→⁷F_J transitions. Features in the vibronic sidebands exhibit similar derived vibrational energies to those observed in the Raman spectra. Fittings of 25 4f⁶ crystal-field energy levels of 2 and 4 have been attempted with some approximations concerning the local Eu³⁺ environments. The ⁵D₀ emission lifetimes are monoexponential and are 0.5 (1,2) and 0.9 ms (3,4) at room temperature.     

Unusual "AB" Spectra in High-Resolution Magic-Angle-Spinning NMR-Studies of Solids

Phosphorus-31CP-MAS spectra of Cd(NO₃)₂(PPh₃)₂ have been obtained as a function of spinning frequency. Although the two ³¹P nuclei are crystallographically equivalent and have the same isotropic chemical shifts in the solid state, they exhibit spinning-rate-dependent MAS spectra which have been analyzed to obtain the value of ²J(P, P). At high spinning rates, the spectra are analogous to "A₂" spectra in isotropic solutions, while at slower spinning rates, the spectra are more characteristic of strongly coupled "AB" solution spectra. The AB spectra are unusual in that δ_A = δ_B and J(A, B) is given by the splitting between the alternate peaks in the four-peak multiplet as opposed to the splitting between the outer and adjacent inner lines. This assignment was confirmed by a 2D CP-MAS J-resolved experiment. The unusual spinning-rate-dependent MAS lineshapes result from recoupling of the J interaction between the two crystallographically equivalent nuclei via anisotropic interactions, i.e., weak homonuclear dipolar coupling and differences in the orientation dependence of the chemical-shift tensors. Such spinning-rate-dependent MAS lineshapes are predicted to be a more frequent observation at higher applied magnetic fields.     

Tunable laser Stark-difference spectra of CD3OH

We present Doppler resolution limited spectra of the P(J) and R(J) multiplets for J ≦ 10 of the 10-μm CO stretch band of ¹²CD₃¹⁶OH using a tunable diode laser. Relative frequencies within the multiplets accurate to ±0.0002–0.0005 cm^?1 are obtained, but no absolute frequencies are given. We are able to assign most of the hindered rotation and K substructure in these multiplets. The assignments are based on analyses of Stark-difference spectra combined with the ground-state microwave data and the intensity variations which are expected theoretically. The ground and excited state A, K = 1 asymmetry splitting parameters are measured to be δ₁″ = (8.5450 ± 0.0080) × 10^?3cm^?1 and δ₁′ = (9.7706 ± 0.0080) × 10^?3cm^?1, respectively. The ground-state value agrees well with the microwave results. A rapid-scan system for recording data and a computer-aided technique for calibrating and plotting the spectra are described.     

Magnetic field orientation dependence of flux pinning in (Gd,Y)Ba2Cu3O7−x coated conductor with tilted lattice and nanostructures

The dependence of the critical current density (J_c) on the orientation of an applied magnetic field was studied for a prototype (Gd,Y)Ba₂Cu₃O_7?x (GdYBCO) coated conductor fabricated by MOCVD on an IBAD-MgO template. Additional rare-earth cations (Y and Gd) and Zr were incorporated into the superconducting film to form (Y,Gd)₂O₃ and BaZrO₃ nanoparticles extended nearly parallel to the a–b planes and to the c-axis, respectively, to enhance the flux pinning. In-field measurement of J_c was carried out with electrical current flowing either along or perpendicular to the longitudinal axis of the tape, while a maximum Lorentz force configuration was always maintained. Details in the angular dependence of J_c were related to the unique structure of the film, specifically the tilt in the GdYBCO lattice and the tilts in the extended (Y,Gd)₂O₃ and BaZrO3 nanoparticles. XRD and TEM were used to study the structure of the coated conductor. The effect of the misalignment between the external field H and the internal field B on the angular dependence of J_c is discussed.     

Theory of the Senftleben-Beenakker effects for NH3 and ND3: Collision integrals

The distorted wave Born approximation is used as a basis for understanding the cross sections which govern the production and relaxation of internal state polarizations, in gaseous ammonia, in the presence of shear flow or thermal gradients. For viscous flow, it is shown that the dominant dipole-dipole interaction leads to the production of [W]⁽²⁾J polarization, but not to any appreciable [J]⁽²⁾ polarization. The essential absence of the usual [J]⁽²⁾ polarization, as produced by the anisotropic dispersion interaction (P₂-potential), is consistent with the smallness of the anisotropy of the dipole polarizability in ammonia and with the suppression of the effect of such shorter ranged interactions (e.g. the P₂ potential) in the presence of a dominant longer ranged interaction (there the dipole-dipole potential). For thermal conduction, it is shown that the dominant dipole-dipole interaction apparently produces predominantly a $\text{WJ(W}{}^2\text{?}\text{5}\text{2}\text{)}$ polarization. The shorter ranged dipole-quadrupole interaction as well as higher multipole potentials produce a W[J]⁽²⁾ polarization, while a cross term between the dipole-dipole and quadrupole-dipole potentials can produce a velocity-independent dipolar polarization, denoted here as Jh¹.     

Collective excitations in the 1-D-ferromagnet CsFeCl3 with singlet ground state

By means of inalastic neutron scattering we have determined the dispersion relation of the magnetic excitations in CsFeCl₃ at different temperatures.The dispersion in c-direction, along the Fe-chains is typically ferromagnetic and in the hexagonal plane antiferromagnetic. Due to the lack of an applicable theory the data were parametrized by the simple heuristic formula:?ω = [2J[1 - cos πq_c] [A + 2J(1 - cos π)q_c)] + [C + J' (1.5 + γ(q))]²]^{$\text{1}\text{2}$}The gap was found to be C = 0.148 THz, the easy plane anisotropy A = 0.308 THz, the ferromagnetic interaction J = 0.148 THz and the antiferromagnetic interaction J' = -0.04 THz. At 1.25 K all excitations had a width smaller than the instrumental resolution ΔE = 0.025 THz. These results can be interpreted as follows: CsFeCl₃ is a singlet ground state system with strong ferromagnetic interaction J along the crystallographic c-axis and weak antiferromagnetic interaction J' in the plane perpendicular to c.In addition we have measured the influence of a magnetic field along the hexagonal c-axis. The splitting found agrees with the assumed level scheme yielding g = 2.5 for the first excited level.     

Biquadratic exchange interaction between Ru5+ ions in (Ru2O9) clusters

The energy levels of a Ru₂O₉ cluster have been calculated, including a higher order spin interaction. The Ru⁵⁺-Ru⁵⁺ coupling is described by the Hamiltonian ?= -2JS₁· S₂ ?j(S₁·S₂)². The temperature dependence of the magnetic susceptibility is used to determine the values of the bilinear J and biquadratic j exchange integrals: J/k = -161K and j/k = 6.6K. The second term in the Hamiltonian corresponds to a fourth order perturbation involving low spin states.     

Magnetostriction and thermal expansion of HoAl3(BO3)4

The magnetostriction and thermal expansion of rare-earth aluminoborate HoAl₃(BO₃)₄ have been studied theoretically. The calculated field and temperature dependences of the multipole moments of the Ho³⁺ ion in HoAl₃(BO₃)₄ made it possible to describe the known experimental data and to predict possible anomalies of thermal expansion. It has been shown that, for the direction of the field B ‖ c, the nonmonotonic character of magnetostriction along the axis a is determined by the multipole moments, the main of which is β _J 〈O ₄ ⁰ 〉. For B ‖ a and B ‖ b, the maximum moments are β _J 〈O ₄ ² 〉and α _J 〈O ₂ ² 〉; their variation with the field and temperature explain well the form of magnetostriction. It has been established that the greater value of magnetostriction Δa/a for B ‖ b than for B ‖ a and the greater value of magnetostriction for the field in the basal plane than for B ‖ c are caused by greater variations in the field of actual multipole moments.     

An investigation of radiative transition probabilities for the A1Σu+-X1Σg+ bands of Na2

The absolute radiative transition probabilities are calculated for previously observed spontaneous emission from A¹Σ_u⁺ (v′,J′) → X¹Σ_g⁺ (v″, J″ = J′ ± 1) reported in the preceding paper and by Woerdman (Chem. Phys. Lett.53, 219 (1978)). The calculations employ accurate hybrid potential energy curves, based on Rydberg-Klein-Rees (RKR), ab initio and long-range results, and a hybrid transition moment function, based on ab initio calculations. These calculated probabilities are compared with the various experimental results; while overall agreement is reasonable, detailed differences do occur.     

Fourier Transform Infrared spectrum of the OCD bending mode in methanol-D1

The infrared (IR) spectra corresponding to OCD bending vibration of asymmetrically deuterated methanol species CH₂DOH have been recorded with a Fourier Transform Spectrometer. The spectrum shows a typical structure of a parallel a-type band. This is expected because the bending vibration mainly executed parallel to the symmetry axis The Q-branch lines are grouped closely around 896 cm⁻¹ and the P- and R-Branches show complex structure. Nonetheless it was possible to assign a-type P- and R-branch lines up to K value of 8 and J value up to about 20 in most cases. The Q-branch lines for higher K values can be followed to about J = 15, the presence of which confirmed the assignments. The observations suggest that in the OCD bend some energy levels are highly interacted by highly excited torsional state from the ground torsional state. A full catalogue is presented along with the effective molecular parameters. An intensity anomaly was also observed in the transitions. So far it has been possible to assign only transitions between e₀ ← e₀ states. Plausible explanations of intensity anomaly are presented. Lastly, a number of optically pumped far infrared (FIR) laser lines have been assigned either to exact or tentative quantum states. These assignments should prove valuable for production of new FIR laser lines.     

The thermal conductivity of the gaseous mixture CH3CN-Ar in a magnetic field

Experimental results are reported for the magnetic field influence on the thermal conductivity of CH₃CN-Ar gas mixtures at various compositions for T = 300 K. The observed field dependence is analyzed in terms of the contributions from the W[J]⁽²⁾ and WJ polarizations.     

Millimeter wave spectrum of glycine

We present new investigations of the millimeter wave spectra of the two lowest-energy conformers of glycine (NH₂CH₂COOH). Measurements of these spectra have been carried out between 75 and 260 GHz using the millimeter-wave spectrometer in Kharkov. The new data set involves rotational transitions with J up to 44 and K_a up to 15 for conformer I and transitions with J up to 43 and K_a up to 14 for conformer II. This represents a more than twofold expansion both in the frequency range and J quantum-number range in comparison with previous investigations. The improved sets of spectroscopic parameters obtained for both conformers provide accurate transition frequencies for the key lines necessary for radio astronomy searches for interstellar glycine.     

2,7-Carbazole and thieno[3,4-c]pyrrole-4,6-dione based copolymers with deep highest occupied molecular orbital for photovoltaic cells

Three kinds of donor–acceptor (D–A) type photovoltaic polymers were synthesized based on 2,7-carbazole and thieno[3,4-c]pyrrole-4,6-dione (TPD). The conjugation of weakly electron (e)-donating 2,7-carbazole and strongly e-accepting TPD moieties yielded a deep highest occupied molecular orbital (HOMO) and its energy level was fine-controlled to be −5.72, −5.67 and −5.57 eV through the incorporation of thiophene (T), thieno[3,2-b]thiophene (TT) and bithiophene (BT) as a π-bridge. Polymer:[6,6]-phenyl-C₇₁ butyric acid methyl ester (PC₇₁BM) based bulk heterojunction solar cells exhibited a high open-circuit voltage (V_OC) in the range, 0.86–0.94 V, suggesting good agreement with the measured HOMO levels. Despite the high V_OC, the thiophene (or thienothiophene)-containing PCTTPD (or PCTTTPD) showed poor power conversion efficiency (PCE, 1.14 and 1.25%) because of the very low short-circuit current density (J_SC). The voltage-dependent photocurrent and photoluminescence quenching measurements suggested that hole transfer from PC₇₁BM to polymer depends strongly on the HOMO level of the polymer. The PCTTPD and PCTTTPD devices suffered from electron–hole recombination at the polymer/PC₇₁BM interfaces because of the insufficient energy offset between the HOMOs of the polymer and PC₇₁BM. The PCBTTPD:PC₇₁BM device showed the best PCE of 3.42% with a V_OC and J_SC of 0.86 V and 7.79 mA cm⁻², respectively. These results show that photovoltaic polymers should be designed carefully to have a deep HOMO level for a high V_OC and sufficient energy offset for ensuring efficient hole transfer from PC₇₁BM to the polymer.     

Electronic g factors eleven atomic states of Zr

The g_j for eleven low-lying levels of Zr I have been measured with the atomic-beam magnetic resonance method. The agreement between the experimental g_J values and theoretical predictions deduced from intermediate coupling wave functions is better than 0.1%.