Cl Nuclei Research Articles

Infra-red and 35Cl nuclear quadrupole resonance studies of hydrogen bonded adducts of 2-chlorobenzoic acid derivatives

The IR and 35Cl NQR spectra of several solid hydrogen bonded adducts of o-chlorobenzoic acids and amines were studied over the broad ΔpKa range. Both IR and NQR spectra yield the indication of the existence of an inversion (critical) ΔpKa range where the proton transfer takes place. The critical point is distinguished by a deep minimum of the position of the gravity centre of the broad protonic band. The mechanism of the transmittance of the charge distribution within the hydrogen bridge on the electric field gradient in the position of quadrupole Cl nuclei attached to the phenyl ring is analysed.

35Cl NQR study of 2,6-dichlorotoluene

The temperature dependence of the NQR frequencies and spin—lattice relaxation time of 2,6-dichlorotoluene are investigated in the temperature range 60–160 K. From the NQR spectral data a possible molecular arrangement is suggested. Besides, the observed T 1( T) behaviour can be explained by using the proposed molecular arrangement, by assuming a relaxation mechanism provided by the intramolecular interaction between the Cl nuclei and the methyl groups. The results are well correlated with those obtained in a previously studied substituted toluene compound, p-toluenesulphonyl chloride.

NMR Study of Covalency in Ferromagnet Rb2CrCl4

NMR measurements of Cl nuclei were carried out to clarify the covalency between Cr 2+ and Cl - ions. By analyzing the NMR spectra, the unpaired spin densities of s-and p-orbitals of Cl - ion are estimated to be f s =0.21% and f σ - f π =-1.1%. Contrary to what was anticipated, the π-bonding is stronger than the σ-bonding.

Electric-charge redistribution in the HCl subunit of hydrogen-bonded dimers B • • • HC1 from Cl nuclear quadrupole coupling: determination of the coefficient F zz of the electric-field-induced field gradient in HCl

An interpretation is given of the chlorine nuclear quadrupole coupling constants X (Cl) for the series of dimers B • • • HCl and B • • • DCl where B = CO, C 2 H 4 , C 2 H 2 , PH 3 , H 2 S, HCN, CH 3 CN, H 2 O and NH 3 . The factors that contribute to the change in X (Cl) on dimer formation are considered in turn. First, account is taken of the effect of bond lengthening of the HCl subunit that occurs on dimer formation. Secondly, the contribution X E to the change in the coupling constant that arises from the electrical effect of B on the field gradient at the Cl nucleus in the dimer is treated at equilibrium in terms of two contributions according to the equation X E = X P + X Q = ‒ eQ {F zz F z + G zz F zz }/ h . The first term X P results from the polarization of the HCl subunit by the electric field F z due to B. The second term X Q arises from the field gradient F zz due to B but modified by the factor (l + γ zz ) = G zz , where γ zz is the usual Sternheimer antishielding factor. F zz is the corresponding factor associated with the field gradient at the Cl nucleus resulting from the polarization of the HCl subunit by the field due to B. The term X Q is directly evaluated using an available Sternheimer antishielding factor. Thirdly, allowance is made for the effect of averaging over the zero-point bending motion of the dimer. Finally, the remaining term X P has then been calculated for each member of the series B • • • HC1 and shown to be linearly dependent on F z as required by the above expression. Hence it has been possible for the first time to make an experimental determination of an F zz value of a gas-phase molecule and we report F zz = ‒116(6) x 10 10 m -1 for the HCl molecule.

Formation and Structure of the Phosphoranyl Radical Derived from 1,2‐Phenylene Phosphorochloridate: a Solid‐State ESR Study

AbstractThe crystal structure of 1,2‐ phenylene phosphorochloridate has been determined. X‐Ray irradiation of these crystals, at low temperature, leads to the formation of a radical exhibiting hyperfine structure with P and Cl nuclei. The corresponding ESR tensors are obtained, and they show that this radical is a phosphoranyl radical adopting a slightly distorded σ* structure. The same species could be produced in frozen solution, its hyperfine tensors are, then, more in accordance with a trigonal‐bipyramid structure. The effects of the host matrix on the stabilization of the structure of phosphoranyl are investigated.

Abinttio calculation of the ionization potentials and hyperfine splitting constants of the radical anions FCl XXX and Cl 2XXX

Employing a CI wavefunction with a DZ+ (2d) basis set, the isotropic hyperfine splitting constants for the F and Cl nuclei in the gas-phase radical anions FCl XXX and Cl 2 XXX were evaluated. The ionization potentials are calculated as 2.10–2.27 eV for FCl XXX and 2.22–2.28 eV for Cl 2 XXX, the latter comparing well with the experimental value of 2.32–2.38 eV.

Structure of electron traps in LiCl solutions studied by ESR

ESR characteristics of visible absorbing electrons in LiCl glasses were studied. Increasing the LiCl concentration caused an increase of the ESR linewidth in both LiCl/H 2O and LiCl/D 2O solutions. This was attributed to the contribution of hyperfine interaction with Cl nucleus. The second moment analysis of ESR spectra showed that one water molecule of each electron trap is substituted by one chloride ion in the concentrated solutions. It was concluded that the electron trap is a Li + hydration shell.

Determination of mutual positions of molecules of CFCl3 dissolved in lattice of CCl4 and adsorbed on silica gel at 77.4�K by means of19F NMR

1. In a solid solution in CCl4, with low concentrations of CFCl3, the second moment M2 of the19F NMR line varies with the square of the concentration. The dependence is in quantitative agreement with the hypothesis that isolated pairs of CFCl3 molecules exist in the solution, analogous to what was found previously in a CFCl3 crystal, and this enables us to estimate the contribution of the Cl nuclei to M2. 2. At low coverages, the dependence of the second moment of the19F NMR lines in adsorbed CFCl3 is explained by nonuniformity of the silica gel surface. 3. Upon freezing liquid CFCl3, a special solid phase is formed in the space between the silica gel grains, for which the form of the NMR line is considerably different from that for the ordinary CFCl3 crystal, and the melting point is lower than for the ordinary crystal.

Asymmetry parameters of the electric field gradient at the 35Cl nuclei of (3-chloropropyl)trichlorostannane

Asymmetry parameters for the electric field gradient at the 35 Cl nuclei of polycrystalline Cl(CH 2 ) 3 SnCl 3 have been measured at 77 K. They are in agreement with a trigonal-bipyramidal structure for the molecule. The electron distribution of the axial chlorine atom in the SnCl 3 group is almost axially symmetric whereas that of the two equatorial atoms and the chlorine atom in the Cl(CH 2 ) 3 group deviate noticeably from the axial symmetry. The deviation is mainly due to the interaction of the lone electron pair of the corresponding chlorine atom with the central tin atom.

35,37Cl and 59Co NMR study of first-stage CoCl 2-GIC

Nuclear magnetic resonance (NMR) of 35,37Cl and 59Co in a CoCl 2-graphite intercalation compound (GIC) is reported. Two spin-echo signals have been observed at 1.4 K. One is a broad signal spread over between 17 MHz and 29 MHz with a peak at 22.5 MHz, and attributed to that due to the Cl nuclei. Another signal has been observed between 230 MHz and 410 MHz, and attributed to that due to the Co nuclei. The observed broadness of the spectra of both signals is consistent with the incommensurate relation between the CoCl 2 lattice and the graphite lattice.

Asymmetry parameters of the electric field gradient at the 35Cl nuclei in compounds of the XC6H4CH2Cl series (X = CH3, Cl)

AbstractThe asymmetry parameters of the electric field gradient at the 35Cl nuclei in polycrystalline compounds of the 2‐, 3‐ and 4‐XC6H4CH2Cl (X = CH3, Cl) series were measured at 77 K. The data obtained directly indicate the almost axial symmetry of the electric field gradient at the 35Cl nuclei, and the participation of the pσ electrons of the chlorine atom of the CICH2 group in the interaction with the geminal sp2 carbon atom in the molecules studied.The experimental η values allow a more precise assignment of the lines in the NQR spectrum of 3‐ClC6H4CH2Cl.

Microwave rotational spectrum of a weakly bound complex formed by hydrogen sulphide and hydrogen chloride

A weakly bound dimer formed by hydrogen sulphide and hydrogen chloride has been identified in the gas phase by means of its rotational spectrum which has been detected with the aid of the sensitive technique of pulsed-nozzle, Fourier-transform microwave spectroscopy. The spectra of eight isotopic species have been analysed to give rotational constants (B0+C0), centrifugal distortion constants DJ and Cl nuclear quadrupole coupling constants Xaa as follows: [graphic omitted]The listed spectroscopic constants allow us to establish that the weak intermolecular linkage occurs through a hydrogen bond, with HCl acting as the proton donor and the S atom acting as the proton acceptor. The S⋯H—Cl nuclei are collinear (or nearly so) with r(S⋯Cl)= 3.8092 A, and the plane of the H2S molecule is almost perpendicular (ϕ= 93.8°) to the line of the hydrogen bond. Conclusions about the relative strength of the hydrogen bond are drawn from analyses of the constants DJ and Xaa.

Distribution of Cl-and Br-Ions in Mixed Crystals (CH3NH3)2Cu(Cl1-xBrx)4

NMR measurements of Cu and Cl nuclei are carried out at 1.75 K to clarify the distribution of Cl - and Br - ions in the slowly grown mixed crystals (CH 3 NH 3 ) 2 Cu(Cl 1- x Br x ) 4 from an aqueous solution. The analysis of the Cu NMR spectra reveals that the Cl - and Br - ions do not distiribute at random. By comparing the NMR intensities of Cl nuclei on the c -axis with those in the c -plane, it is concluded that most of Cl - ions preferentially occupy the positions in the c -plane.

EPR and ODMR investigations of defect centres in ZnTe:Cl

We report EPR and ODMR (optically detected EPR) studies of Cl doped ZnTe that show a fraction of the chlorine participating in complex, deep-level defects. Photoexcitation at T < 50 K creates an EPR spectrum corresponding to an S = 12 centre with nearly isotropic g factor (g = 1.96) and hyperfine interaction with a Cl nucleus. Weak, satellite EPR lines correspond to interaction with three equivalent Te nuclei and a low abundance, I = 12 nucleus X, which could be either an Sn, Pb or Cd nucleus. Our model for this trigonal symmetry defect is a Cl on a Te site with X on a neighbouring Zn site. ODMR studies at 2 K of an emission band peaking near 770 nm gives the Cl centre EPR spectrum and in addition the spectrum of a trigonal acceptor centre with highly anisotropic g-tensor (g″ = 2.65, g⊥ ≅ 0). The ODMR work shows that the 770 nm emission results from recombination of the electron of the deep Cl centre with the hole of the trigonal acceptor centre.

35Cl NQR Spectra of several 2,2-bis- p-chlorophenyl chloroethane derivatives

Measurement of NQR line frequency at 77 K have been performed for the following compounds: 1-chloro-2,2-bis-(p-chlorophenyl) ethylene (DDMU), 1,1-dichloro-2,2-bis-(p-chlorophenyl) ethylene (DDE), 1,1-dichloro-2,2-bis-(p-chlorophenyl) ethane (ODD), 1,1,1-trichloro-2,2-bis (p-chlorophenyl) ethane (DDT). An attempt to assign spectrum lines to particular Cl nuclei in a molecule has been made. Molecular and crystallographic inequivalences occurring in these compounds have been considered. Comparison of the NQR and crystallographic data revealed the influence of phenyl rings conformation on electric charge distribution in the studied molecules.

Statistical theory of nuclear neutrino capture

Abstract The statistical theory of nuclear neutrino capture is extended to include first-forbidden transitions. A comparison with the theory of Bahcall and Frautschi is made. It is found that the present theory predicts neutrino capture cross sections which are smaller than those of Bahcall and Frautschi by a factor 2–3 for neutrino energies less than 50 MeV when first-forbidden transitions are dominant. Calculation of the cross section is made for the process in which 37 Cl nuclei capture electron neutrinos that are emitted in muon decay. The present calculation gives a cross section which is around one half of that of Donnelly and Haxton. Finally the contributions of the highly excited states in 37 Ar to the neutrino capture cross section are evaluated. It is shown that the contributions from the highly excited states ( E > 6.02 MeV) to the neutrino capture cross section amount to 60% for E v = 50 MeV.

Temperature dependence of spin-relaxation times of protons in liquids

Temperature dependences of the spin–lattice and the spin–spin relaxation times of protons in 1,1,2,2-tetrabromoethane(CHBr2CHBr2), ethylene glycol(OHCH2CH2OH) and trichloroethene (HCClCCl2) were investigated. The spin–lattice relaxation times of 1,1,2,2-tetrabromoethane and ethylene glycol exhibit minima at 229 and 227 K respectively. Theoretical calculations are made by assuming that dipolar interactions between the H—Br, H—H and the H—Cl nuclei in the compounds show good agreement with the experimental results. In 1,1,2,2,-tetrabromoethane and ethylene glycol only the rotational motions of molecules lead to spin-relaxation; however, in trichloroethene both the rotational and translational motions are effective.

A model for the strength function of deeply bound hole states

A comparison of measured and calculated ld 5 2 proton-hole strength distributions in a series of Cl, K and Sc nuclei demonstrates the large effect of phonon-hole coupling on the intermediate structures of the hole strength distribution. A model calculation allows us to study the influence of the high-lying hole strengths which cannot be observed in experiments on occupation probabilities, centroid energies and spreading widths.

NMR study of the magnetisation of the nearly two-dimensional heisenberg ferromagnets (CnH2n+1NH3)2CuCl4with n=1,2,3,4,8,10

The magnetisation of the nearly two-dimensional weakly anisotropic ferromagnets (CnH2dn+1NH3)2CuCl4 has been studied by means of Cu and Cl nuclear magnetic resonance. The hyperfine interaction of Cu and Cl nuclei and the Cu2+ spin direction were determined. The field dependence of the magnetisation has been measured in the range 0 to 10 kOe. This allowed the intralayer exchange integral J to be determined using simple spin-wave theory taking into account experimental magnetic anisotropy and interlayer exchange. The temperature dependence of spontaneous magnetisation measured in the range 1.4 to 4.2K is well described by the theory using this J value.

On the nature of molten CuCl

A recent suggestion that molten CuCl is a covalent molecular liquid (ibid., vol.8, p.895 (1975)), is contradicted by NMR relaxation time measurements of the Cu and Cl nuclei in this system. Rather the data are consistent with an ionic liquid description.