About the concentration dependence of the anisotropy in the magnetic susceptibility of some aromatic compounds in the liquid phase,studied by NMR

Magnetic field induced quadrupolar line splittings in the ²H NMR spectra of pyridine and metadinitrobenzene are reported. From the splittings the anisotropy in the magnetic susceptibility Δ_x has been deduced. The concentration dependence of the quadrupolar magnetic field effect, and hence of Δ_x, of nitrobenzene, metadinitrobenzene and naphthalene has been investigated. The effect of different solvents has also been studied. Environmental effects of Δ_x have been found to be substantial in several cases. The relation of the present experiments with the Cotton-Mouton effect is discussed in detail.     

Angular dependence of 1H- and 2H-NMR spectra of water and methanol absorbed in cellulose triacetate film

¹H- and ²H-NMR spectra of water (H₂O and D₂O) and methanol (CH₃OD and CD₃OH) absorbed in cellulose triacetate films have been observed as a function of the angle θ between the film surface and the magnetic field. ¹H-NMR signals of H₂O and CH₃OD are doublets and triplets due to dipole interactions, respectively. ²H-NMR signals of D₂O, CD₃OH, and CH₃OD are doublets due to quadrupole splittings. The magnitudes of these splittings change depending on θ. The analysis of the angle-dependent patterns indicates that the motionally averaged axes of the dipole and the quadrupole moments orient in the direction perpendicular to the film surface. The alignment of water and/or methanol molecules originates from the film morphology, which is anisotropic in the perpendicular direction. From the angle dependence of the chemical shift, the volume diamagnetic susceptibility of the film is estimated to be 0.44 ppm.     

The electric saturation of molecular alignment in liquid nitrobenzene as studied by NMR

Quadrupolar line splittings in the ¹⁴N and ²H spectra of liquid nitrobenzene, induced by an external electric field, were studied up to very high electric field strengths (E ≈ 1.8 × 10⁷ V m^?1). At moderate fields the line splittings are proportional to E²; at the fields attained in the present experiments higher order effects become detectable. This phenomenon is related to electric saturation: the change of the permittivity in a strong electric field. Nitrobenzene has been reported to exhibit an anomalous saturation effect of the permittivity, but the saturation of the molecular alignment appears to be normal     

Observation of 2izsz order in NMR relaxation studies for measuring cross-correlation of chemical shift anisotropy and dipolar interactions

The cross-correlation spectral density of chemical shift anisotropy and dipolar interactions in isotropic solution of methyl formate is measured using a novel NMR technique designed to monitor the appearance of longitudinal two-spin order 2I_zS_z during inversion recovery. The result is tentatively interpreted in terms of the orientation of the ¹³C-¹H internuclear vector with respect to the principal axes of the ¹³C chemical shift anisotropy tensor of the carboxyl group.     

Determination of the electric field gradient tensor in ferrous chloride tetrahydrate using a polarized mössbauer source

The orientation of the electric field gradient tensor at the iron nucleus in a single crystal of FeCl₂·4H₂O has been determined using a polarized Mössbauer source of ⁵⁷Co in iron metal. The data analysis embodied an accurate thickness correction for the polarization of the absorption cross-section. The principal axis of the tensor lies close to the FeCl bonds of the trans-octahedral FeCl₂(H₂O)₄ unit, but the minor axes are directed between the FeO bonds. The value of the asymmetry parameter obtained, n = 0.40 ± 0.15, is significantly larger than previous estimates.     

Crystal field effects on the ground and lowest excited triplet states of benzene isotopes in a borazine host crystal

The phosphorescence spectra of the C₆H₆C₆H₅D₁p-C₆H₄D₂symp-C₆H₃D₃, C₆D₆ and ¹³CC₅D in a borazine host crystal are analyzed at high resolution. The spectral lines are sharp (～2 cm^?1 wide) indicating that the impurity molecules occupy a unique site in the borazine lattice which is probably substitutional. The phonon sidebands are weak,giving clean, well-resolved spectra much like those of isotopic mixed crystals. In contrast, however, the crystal field effects on the ground state vibrational levels are much smaller than those found for isotopic mixed crystals. The gas-to-crystal shifts are very small, the vibrational degeneracies are not removed and orientational splittings are only observable for a few select vibrational levels. For most vibrational levels and for the derivation of selection rules one can asume the effective crystal site symmetry to be D_3d. The data provide the first conclusive evidence that the splitting observed in the benzene phosphorescence spectrum results from a distortion of the molecule when excited to the zeroth vibrational level of the T₁ state. Furthermore, the data suggest that the distortion is intrinsic in nature (i.e.,is not caused by the crystal field).     

Molecular orbital calculations on transition metal complexes : XX. The π-cyclopentadienyl-π-benzene complexes of chromium and manganese

INDO SCF MO calculations are reported for the complexes (C₅H₅)M(C₆H₆) (M = Cr and Mn) and for the corresponding cations. A ²A₁ ground state is correctly predicted for the neutral Cr system, and other experimental quantities are satisfactorily reproduced. The dominantly metal d-levels yield the H^core sequence e₂ < a₁ < _e1 and the principal interactions were found to be those between the metal e₁ level and the π-orbitals of the C₅H₅ ligand, and between the metal e₂ level and the ligand C₆H₆ π-orbitals. From the state energies of the formally 3d⁵ species estimates were made of the one-electron 3d splittings in the ligand field model, and comparisons made with similar results for M(C₅H₅)₂, M(C₆H₆)₂, and (C₅H₅)M(C₇H₇) systems: these indicated the general validity of the bonding scheme in which the extent of the metal—ligand interaction via the e₁ and e₂ 3d levels varied systematically with the sizes of the ligand rings.     

The Fe2+ chelate of hydrazinecarboxylic acid studied by the Mössbauer effect

The chelate compounds K[Fe(hyc)₃] and N₂H₅[Fe(hyc)₃]·H₂O (hyc = N₂H₃COO) were studied by the Mössbauer effect of ⁵⁷Fe at various temperatures. At room temperature the quadrupole splitting parameter is 2.77 mm/sec for K[Fe(hyc)₃] and 2.35 mm/sec for N₂H₅[Fe(hyc)₃]·H₂O, and the center shift is 1.08 mm/sec for both compounds. The temperature dependences of the quadrupole parameters yielded the crystal field splittings of the ⁵T_2g levels of the Fe²⁺ ions which indicate large trigonal distortion of the Fe(hyc)₃ anion. Using a molecular crystal-like treatment of the ferrous ion vibrations the temperature dependence of the recoilless fraction gave an effective Debye temperature Θ_D = 71°K for K[Fe(hyc)₃] and Θ_D = 90°K for N₂H₅[Fe(hyc)₃]·H₂O. No evidence for magnetic ordering was found down to 4.5°K in either compound.     

On the anisotropy of the intermolecucular potential of the CO2-Ne system in the repulsive short-range region

Ab-initio computations at the STO-3G level have been performed on CO₂-Ne. The short-range interactions are roughly proportional to Σ_ir_i^?12, where the r_i are the distances from neon to the atoms in CO₂. In this empirical approximation, the anisotropy effects are conveniently revealed by the proportionality coefficient whose value depends on the angle between the OCO and C-Ne axes.     

Effect of the Magnetic Field on the Supramolecular Structure of Chiral Smectic C Phases: 2H NMR Studies

We present a theoretical and experimental ²H NMR study of the effect of external magnetic fields on the supramolecular organization of chiral smectic liquid‐crystalline mesophases, such as SmC* and re‐entrant SmC*. Three experimental cases in which the supramolecular helical structure of the smectic C* phase is unwound by a magnetic field (H), parallel to the helical axes of this phase, are discussed in detail. Unwinding of the helical structure is described by using a theoretical model based on the Landau‐de Gennes theory, which allows us to explain the transition temperatures among the SmA, SmC*, and uSmC* phases. The energy‐density behavior in the vicinity of the transitions and the value of the critical magnetic field H_C for unwinding the helical structure are discussed by applying this model to three ferroelectric smectogens ( MBHB , 11EB1M7 , ZLL7/* ), which are studied by ²H NMR spectroscopy at different magnetic fields (from 2.4 to 9.4 Tesla). Furthermore, the tilt angle of the three smectogens in the SmC* phase has been directly evaluated, for the first time, by comparing the quadrupolar splittings at different magnetic fields. In one case, ²H NMR angular measurements are used to obtain the tilt angle in the re‐entrant smectic C phase.     

The g-value of the 2E state of K3CR(CN)6 and the lower symmetry field

The ⁴A₂ → ²E transition of potassium chromicyanide has been studied under magnetic field. It has been found that the g-value is nearly isotropic, quite unlike the case of ruby. An attempt has been made to explain the zero-field splittings of ^2E, ²T₁ and ²T₂ states and the g-value of the ²E state on the assumption that the distant ions are mainly responsible for lowering of symmetry of the crystal field from O_h. A reasonable choice of parameters can make the calculated values agree with the observed ones.     

Angular dependence of 1H- and 2H-NMR spectra of H2O and D2O absorbed in cellulose acetate film

¹H- and ²H-NMR spectra of H₂O and D₂O absorbed in cellulose acetate films were observed while changing the angle between the plane of the film and the magnetic field. ¹H-NMR spectra show dipolar splittings that vary depending on the angle. The splitting has a maximum when the surface of the film is perpendicular to the magnetic field. From the angular dependence of the dipolar splitting, it is recognized that the proton-proton dipolar axis of water molecules tends to orient perpendicularly to the surface of the film. ²H-NMR spectra that show quadrupolar splittings also indicate that the quadrupolar axis tends to orient perpendicularly to the film. The so-called bound water and free water in the film can exchange rapidly on the NMR time scale, so that the line width and the splitting of the NMR spectra become smaller as the amount of water in the film increases. From the temperature dependence of line widths, the apparent reorientational activation energy of water molecules in the film is estimated to be 25 kJ/mol from ¹H-NMR and 31 kJ/mol from ²H-NMR.     

Investigation of electron correlation on the theoretical prediction of zero-field splittings of 2Π molecular states

First-order ²Π zero-field splittings are computed for the H₂S⁺, BO, NO, CH, CO⁺ and OH ground electronic states by employing ab initio multi-configuration wavefunctions and by including all one-and two-electron spin-orbit interactions in a gaussian AO basis explicitly in the theoretical treatment.     

Thermodynamic interactions in rubbery polymer/gas systems

The Flory–Huggins interaction parameters χ for 23 gases (He, Ne, Ar, Kr, Xe, H₂, N₂, O₂, N₂O, CO₂, CH₄, C₂H₄, C₂H₆, C₃H₆, C₃H₈, 1,3-C₄H₆, four C₄H₈'s, n-C₄H₁₀, iso-C₄H₁₀, and n-C₅H₁₂) in five rubbery polymers (1,2-polybutadiene (PB), poly(ethylene-co-vinyl acetate)) (EVAc), polyethylene (PE), polypropylene (PP), and poly(dimethyl siloxane) (PDMS) were determined from either literature data on Henry's law coefficient and partial molar volume or those on sorptive dilation for each polymer/gas system. Values of χ for the gases increased in the order of PDMS < PP ≡ PB < EVAc ≡ PE. Among the gases except He and H₂ whose χ values are not reliable, Ne and Xe have respectively the highest and the lowest values of χ for the polyolefins. The χ values of the hydrocarbons were compared together with previously reported χ values of n-alkanes C₃-C₁₀. The dependencies of χ upon concentration and temperature were discussed on the basis of the literature data. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 1049–1053, 1997     

Angular dependence of 1H-NMR and 2H-NMR spectra of water absorbed in cellulose film

¹H-NMR and ²H-NMR spectra of water (H₂O and D₂O) absorbed in Visking cellulose tubing have been observed as a function of the angle Θ between the film surface and the magnetic field. ¹H-NMR spectra show broad lines, and the chemical shift and the linewidth depend on Θ. From the angular dependence of the chemical shift, the anisotropic volume diamagnetic susceptibilities of the film are determined, i.e., χ_∥ in the direction longitudinal to the tubing (stretched direction) is 0.43 ppm, and χ_⊥ in the transverse direction is 0.57 ppm. The different values of χ_∥ and χ_⊥ afford an evidence of the anisotropy of the film. ²H-NMR spectra of D₂O absorbed in the film show quadrupole splitting which also depends on Θ. The angular dependences of the linewidth (¹H-NMR) and the quadrupole splitting (²H-NMR) indicate that the H? H axes of the water molecules have a tendency to orient in the direction longitudinal to the film surface.     

Configuration interaction study of H2 using a modified slater-type orbital

A non-standard 1s basis function, χ = (1 + ar²) exp(?ζr), is used to approximate the ground state of the hydrogen molecule in a configuration interaction framework and using numerical integration over MO's. Results are compared to the traditional 1s STO.     

Laser induced fluorescence spectroscopy of van der Waals complexes of aniline with N2, H2, and CH4 formed in a supersonic free jet

The laser induced fluorescence spectra for the Ã(¹B₂)X̃(¹A₁) transition of van der Waals (vdW) complexes of aniline with N₂, H₂, and CH₄ have been observed. Based on the analysis of the rotational structure of the spectra, it is suggested that two vdW conformers exist for the N₂aniline complex though only one conformer is identified for the other complexes. In the electronically excited state of the CH₄aniline complex, energy level splittings are observed and attributed to the intramolecular rotation of CH₄.     

Interpretation of experimental Mössbauer quadrupole splittings of iron pentacyanide complexes using molecular orbital theory

Semiempirical self-consistent-field molecular-orbital calculations are carried out for six iron-pentacyanide complexes and are used to interpret their experimental Mössbauer quadrupole splittings. Probable orientations are identified for the C₆H ₅ ^? and NO ₂ ^? groups in Fe(CN)₅NOC₆H ₅ ^?3 and Fe(CN)₅NO ₂ ^?4 . Calculations on Fe(CN)₅NO^?2 and Fe(CN)₅NO^?3 can simultaneously be brought into agreement with experiment by reparametrization to make the NO group more positively charged. All the calculations indicate the importance of including all the Fe 3d and 4p orbitals in the calculations and of considering neighboring-atom effects.     

Anisotropy of dielectric relaxation in crystal form II of poly(vinylidene fluoride)

The anisotropy of the crystalline relaxation (α relaxation) in oriented poly(vinylidene fluoride) in crystal form II has been studied. The dielectric increment Δε is analyzed on the basis of the two-site model. A linear relation between Δε/χξ and cos²θ is obtained, where χ is the degree of crystallinity, ξ is the ratio of the internal field to the applied field, and θ is the angle between the applied electric field and the molecular axis. The dipole moment changes direction only along the molecular axis in the relaxation in crystal form II; the molecular motion cannot be explained by chain rotation around the molecular axis. Possible models for the α relaxation are proposed: change in conformation with internal rotation can occur in the crystalline chains, and defects in the crystalline regions play an important role in the α relaxation.     

Emission spectra of supersonically cooled methyldiacetylene cations

The ā²E → X?²E (Σ= + $\text{1}\text{2}$, - $\text{1}\text{2}$) electronic transitions of rotationally/vibrationally cooled CH₃CCCCH^- cation, as well as the d₁-/d₃-/d₄-substituted species, were studied by emission spectroscopy. Ion emission was obtained by electron impact on the neutral species seeded in a helium supersonic free jet. Vibrational frequencies in both electronic states are inferred to within ±1 cm^-1. Spin-orbit splittings are observed and interpreted on the basis of non-linear vibronic couplings. Rotational subbands are observed, yielding rotational and Coriolis parameters as well as rotational temperatures.