Chlorine Nuclei Research Articles

Nuclear quadrupole coupling in Cl2C=CHCl and Cl2C=CH2: Evidence for systematic differences in orientations between internuclear and field gradient axes for terminal quadrupolar nuclei

The nuclear quadrupole hyperfine structure in rotational transitions of parent isotopomers of trichloroethylene, Cl235C=CH35Cl, and 1,1-dichloroethylene, Cl235C=CH2, was measured at sub-Doppler resolution with a pulsed supersonic beam, cavity Fourier transform microwave spectrometer. The complete inertial and principal nuclear quadrupole coupling tensors of all chlorine nuclei are determined. The three chlorine tensors for trichloroethylene have been assigned unambiguously to the structural positions of the chlorine nuclei on the basis of ab initio field gradient calculations. For both molecules the directions of the symmetry z axes of the field gradients at the chlorine nuclei show small, but significant, angular deviations δ from the directions of the respective CCl bonds. These differences are found to be well reproduced by ab initio calculations at the self-consistent field (SCF) level, with small sensitivity to the basis set. Similarly accurate reproduction of δ is demonstrated for various quadrupolar nuclei X=N, Cl, Br, and I terminal to CX bonds in several molecules. Consideration of contributions to the electric field gradient reveals that the small angular deviations δ reflect intermediate range molecular asymmetry about the bond axis to the measuring nucleus, at distances 1–4 Å away. In the case of two neighboring atoms bonded to the same intermediate atom as the probe nucleus the direction of the z axis at this nucleus will, in general, deviate towards the neighbor with greater Z, and therefore, with greater local electron density.

Nuclear Quadrupole Coupling in 1,1,1-Trichloroethane: Inertial and Principal Tensors for35Cl and37Cl

The hyperfine structure in theJ= 1 ← 0 andJ= 2 ← 1 transitions of35Cl3CCH3and35Cl237ClCCH3was resolved by utilizing the sub-Doppler resolution of a pulsed supersonic beam, cavity Fourier transform microwave (FTMW) spectrometer. The complete inertial and principal quadrupole tensors of the chlorine nuclei are determined. The symmetric top treatment for35Cl3CCH3and the asymmetric top treatment for35Cl237ClCCH3are found to yield identical results for the principal tensor components of the35Cl nucleus. The quadrupole asymmetry parameter η for the chlorine nuclei in 1,1,1-trichloroethane is small, which indicates nearly cylindrical symmetry of the field gradient. Nevertheless, there is evidence for some deviation of thezsymmetry axis of the field gradient from the direction of the C–Cl bond.

Millimeter-Wave Rotational Spectra of the37Cl Species of 1,1,1-Trichloroethane

The mm-wave rotational spectrum of the three isotopic species which result from37Cl isotopic substitution in 1,1,1-trichloroethane was studied in the region 121–472 GHz, and for transitions withJ″ up to 100. The symmetry equivalence of the three chlorine nuclei makes the rotational spectrum of35Cl237ClCCH3comparable in intensity to that of the parent species, so that it accounts for a large proportion of the mm-wave spectral intensity. Accurate spectroscopic constants have been determined for all studied isotopic species, and evolution of their values relative to those of the parent species has been studied. The magnitudes of the constanth3in the asymmetric top37Cl1and37Cl2species are in excellent agreement with that for the symmetric top parent species and show that, under suitable conditions, the measurement of the asymmetric top species arising from isotopic substitution can provide a less demanding route for determination ofh3than in the parent symmetric top molecule.

Born–Oppenheimer type separation in the study of the dynamics: Application to photodetachment of ClHCl− and ClDCl−

The Born–Oppenheimer type separation between light and heavy nuclear motions is applied to the study of the dynamics of the ClHCl and ClDCl systems. Approximate and elaborate approaches are used to calculate the photodetachment spectra of the ClHCl− and ClDCl− anions. The approximate approach is based on a Born–Oppenheimer approximation where the nuclear wave function of the ClHCl or ClDCl systems is obtained as a single product of two wave functions which describe the motion of the light H(D) nucleus for clamped chlorine nuclei and the motion of the heavy chlorine nuclei, respectively. The elaborate approach is a multistate description which goes beyond the Born–Oppenheimer approximation. The relevant close coupling equations are solved numerically subject to proper photodissociation asymptotic conditions. The results obtained in this approach confirm the validity of the approximate one and provide additional information on the ClH+Cl and ClD+Cl decay channels. Resonances are obtained at energies of 0.640 eV and 0.899 eV for the ClHCl system, and at 0.538 eV and 0.715 eV for the ClDCl system. They are identified as shape or Feshbach resonances and analyzed in terms of the normal modes of a linear symmetrical triatomic molecule.

The microwave spectrum of the NCl radical in the electronically excited (a 1Δ) state

The pure rotational spectrum of the 14N35Cl radical in the first electronically excited a 1Δ state was detected by microwave spectroscopy. The NCl radical was produced by a dc-glow discharge of an N2 and Cl2 mixture between 175–210 K. Seven rotational transitions for υ=0 and five for υ=1, showing hyperfine structures due to the nitrogen and chlorine nuclei, were observed in the 162–404 GHz region. The rotational, centrifugal distortion, and hyperfine coupling constants including nuclear spin–rotation coupling constant of the chlorine nucleus were determined accurately by a least-squares analysis of the measured frequencies. The equilibrium structural parameters were derived and discussed.

Conformational Analysis of Chloromethylenimine and its Hydrogen-Bonded Dimers with Water from the Study of Nuclear Quadrupole Interactions

Abstract A molecular conformation study on N-Chloromethylenimine and its 1:1 dimeric form with water has been carried out using the ab-initio method at 6-31 G and 6-31 G* basis set. We consider the two most stable conformers of the N-chloromethylenimine -water binary mixture involving double hydrogen bonds. In all cases the proton affinity has been calculated. Each system considered in this work has the nuclear quadrupole interactions of the nitrogen and chlorine resonant nuclei which have been calculated and compared. It is found that the nuclear quadrupole coupling constant for the nitrogen nucleus increases in the hydrogen bonded complexes and decreases for the chlorine nucleus compared to the monomeric values. The influence of proton affinity is reflected in the nuclear quadrupole coupling constant.

Solid-state nuclear magnetic resonance investigations on chlorocyclophosphazenes

The present study deals with solid-state nuclear magnetic resonance (NMR) investigations on hexachlorocyclotriphosphazene (N 3P 3Cl 6) and T and K form of octachlorocyclotetraphosphazene (N 4P 4Cl 8). Using 31P NMR we have recorded spectra of different magic-angle spinning (MAS) frequencies and static powder spectra. By means of the analysis of spinning sideband intensities the isotropic chemical shifts and the principal values of the chemical shift tensor could be determined. Because of the interactions between phosphorus and the neighbouring chlorine nuclei in the MAS spectra of N 3P 3Cl 6 and N 4P 4Cl 8 more lines were found to exist than was expected with regard to the isotropic chemical shift values according to the crystallographic phosphorus positions. To support this evidence solid-state spectra of the geminally disubstituted compound 2,2,4,4-tetrachloro-6,6-bisthiophenylcyclotriphosphazene [N 3P 3Cl 4(SPh) 2] were used. In addition, by means of the individual gauched localized orbitals (IGLO) method 31P NMR chemical shifts, principal values and the orientation of the principal axes of the shielding tensor were calculated for the chlorocyclophosphazenes.

The Rotational Spectrum of Chloroform in Its Ground and Excited Vibrational States

The rotational spectrum of the ground state, the excited A states ν3, 2ν3 and probably ν2, and the lowest E state ν6 of CH35Cl3 have been measured. The ground state microwave spectrum was analyzed to obtain nuclear quadrupole coupling constants. These are consistent with the electric field gradient at each chlorine nucleus being cylindrically symmetrical about the C-Cl bond. Rotation-vibration parameters were obtained for all vibrational states. The spectrum of the doubly degenerate ν6 state showed strong l resonance, which enabled the centrifugal distortion constant DK and the Coriolis coupling constant ζ6 to be determined.

Oxidation of a tricoordinated CuI complex to a tetracoordinated CuII species. A single- EPR study

Bis(N-methylimidazolidinethi-2-one)copper(I) chloride has been synthesized and its crystal structure determined. X-Irradiation of a single crystal of this compound leads to the formation of a CuII complex which was studied by EPR: it was shown that this species results from the addition of a radiogenic Cl atom on the CuI precursor. The structural changes induced by this reaction are revealed by the g-tensor and by the hyperfine tensors of one copper and two chlorine nuclei. The structure of this S2Cl2Cu type complex was compared with other sulfur- or chlorine-containing CuII complexes.

35Cl NQR Spin‐Spin Relaxation Mechanism in Mg(D2O)6SnCl6 and Ni(H2O)6SnCl6 Crystals

AbstractThe temperature dependence of the 35Cl NQR spin‐spin relaxation times T2Q in Mg(D2O)6SnCl6 and Ni(H2O)6SnCl6 is measured. T2Q of the former compound is determined mainly by the magnetic dipolar field at the chlorine nucleus produced by the intramolecular nuclei, the tin nucleus, and five other chlorine nuclei in the [SnCl6]2‐ ion. T2Q of the latter compound is governed mainly by the local magnetic field at the chlorine site produced by the intramolecular nuclei and unpaired electrons in the Ni2+ ions. The correlation time for electron‐spin flips due to the exchange interaction among neighbouring unpaired electrons is evaluated from T2Q. A general behaviour of halogen NQR T2Q in diamagnetic and paramagnetic insulators is summarized.

Level crossing resonance due to chlorine nuclei in a free radical

Muonium adds to allyl chloride, CH2=CHCH2Cl, to form two radicals: MuCH2CHCH2Cl (main product) and CH2CHMuCH2Cl (minor product). Both radicals were fully characterized byμSR andμLCR. In the main product, the LCR lines due to the35Cl and37Cl nuclei were observed. Also, the temperature dependence of various hyperfine coupling constants (hfc) indicates that both Mu and Cl eclipse the unpaired electronp 2-orbital in the minimum energy conformation. For the fragment-CH2Cl, the presence of Mu in theβ′-position is found to affect significantly the hfc of Cl in theβ-position; an internal rotational barrier of 12 kJ mol−1 was estimated using a simpleV 2 torsional potential.

Quadrupole-Nuclear Relaxation Induced by Dynamic Disorders

The 35 Cl NQR spin-lattice relaxation times T 1Q in Ni(H 2 O) 6 SnCl 6 and Mg(H 2 O) 6 -SnCl 6 are determined mainly by the fluctuations of the electronic magnetic fields caused by electron-spin flips and of the electric field gradients due to lattice vibrations, respectively. In addition, we have observed a double minimum and a dip in T 1Q for the Ni and Mg compound, respectively. This arises from the fluctuation of the electric field gradients at the chlorine nuclei caused by reorientational motions of the nearby cations that result in slight dynamic disorders of the proton sites. This type of relaxation mechanism has not been observed extensively so far, because the disorder in question is limited only to such one as can affect the NQR relaxation but at the same time does not prevent us from observing the NQR signals. The nature of the relaxation mechanism is discussed.

Excitation of interstellar hydrogen chloride

We have computed new rate coefficients for the collisional excitation of HCl by He, in the close-coupled formalism and using an interaction potential determined recently by Willey, Choong, & DeLucia. Results have been obtained for temperatures between 10 K and 300 K. With the use of the infinite order sudden approximation, we have derived approximate expressions of general applicability which may be used to estimate how the rate constant for a transition (J to J prime) is apportioned among the various hyperfine states F prime of the final state J prime. Using these new rate coefficients, we have obtained predictions for the HCl rotational line strengths expected from a dense clump of interstellar gas, as a function of the HCl fractional abundance. Over a wide range of HCl abundances, we have found that the line luminosities are proportional to abundance(exp 2/3), a general result which can be explained using a simple analytical approximation. Our model for the excitation of HCl within a dense molecular cloud core indicates that the J = 1 goes to 0 line strengths measured by Blake, Keene, & Phillips toward the Orion Molecular Cloud (OMC-1) imply a fractional abundance n(HCl)/n(H2) approximately 2 x 10(exp -9), a value which amounts to only approximately 0.3% of the cosmic abundance of chlorine nuclei. Given a fractional abundance of 2 x 10(exp -9), the contribution of HCl emission to the total radiative cooling of a dense clump is small. For Orion, we predict a flux approximately 10(exp -19) W/sq cm for the HCl J = 3 goes to 2 line near 159.8 micrometers, suggesting that the strength of this line could be measured using the Infrared Space Observatory.

A three-dimensional study of the ClHCl dynamics using the light—heavy nucleus Born—Oppenheimer separation

The Born—Oppenheimer type separation between the light and heavy nuclear motions is applied to the dynamics of the ClHCl system. Among the hydrogenic states which describe the motion of the H atom for clamped chlorine nuclei, certain specific states are shown to explain the main structures of the photodetachment spectrum of ClHCl −. Three resonances are obtained at scattering energies SE=0.639, 0.899 and 0.932 eV and are analyzed in terms of the normal modes of a linear symmetrical triatomic molecule. The calculated photodetachment spectrum is compared to previous theoretical and experimental data.

ESR Investigation of a Spin 1/2 Chlorine-Associated Defect in Synthetic FeS2 Crystals

A new type of spin 1/2 chlorine-associated defect species has been observed by ESR in as-grown, sulfur-deficient FeS2 crystals grown by the method of chemical vapor transport using ICl3 as the transport agent. The ESR spectrum of this defect species exhibits a low symmetry and a weak hyperfine interaction with a single chlorine nucleus. The g-factor anisotropy indicates that this species is most likely a hole species, having a p5 electron configuration and localized at a sulfur atom. We assign this defect species as an (SCl)2- impurity defect, replacing (S-S)2- and locally associated with a Fe2+ vacancy created probably to compensate for the substitutional Cr3+ impurities.

NMR study of the T1 relaxation dispersion in the smectic mesophase of 4-chlorophenyl 4-undecyloxybenzoate.

An experimental study of the Larmor frequency dependence of the proton spin-lattice relaxation time [${\mathit{T}}_{1}$(${\ensuremath{\nu}}_{\mathit{L}}$)] was carried out in the range of ${\ensuremath{\nu}}_{\mathit{L}}$=7 to 30 MHz. Two relaxation times describing the evolution of the longitudinal magnetization have been found to have different behaviors. One of them has been assigned to the relaxation of the protons belonging to the alkyl chain -${\mathit{T}}_{1}^{\mathrm{alkyl}}$(${\ensuremath{\nu}}_{\mathit{L}}$)-. The ${\mathit{T}}_{1}^{\mathrm{alkyl}}$(${\ensuremath{\nu}}_{\mathit{L}}$) dispersion behaves normally without signs of $^{1}\mathrm{\ensuremath{-}}^{35}$Cl cross relaxation. The second one, called ${\mathit{T}}_{\mathit{a}\mathrm{\ensuremath{-}}\mathit{c}}$, has a partial contribution from the protons bonded to the molecular core and those of the alkyl chain. Well-defined $^{1}\mathrm{\ensuremath{-}}^{35}$Cl quadrupole dips (QD) have been observed in the ${\mathit{T}}_{\mathit{a}\mathrm{\ensuremath{-}}\mathit{c}}$(\ensuremath{\nu}) dispersion curve, due to a cross-relaxation process between the core protons and the chlorine nucleus of the molecule. The shape of the dips are not symmetric, and cannot be fitted by Gaussian or Lorentzian functions. Computer simulations with asymmetric functions previously used in line-shape analysis of incommensurate systems and organic glasses are discussed.

Spectroscopic studies on copper(II) complexes of chiral cyclens: [CuN 4Cl] chromophores varying from square pyramidal to trigonal bipyramidal stereochemistry

A series of five copper(II) complexes with four geometrically isomeric ligands of 1,4,7,10-tetrabenzyl-2,5,8,11-tetraethyl-1,4,7,10-tetraazacyclododecane and with (2 R,5 R,8 R,11 R)-2,5,8,11-tetraethyl-1,4,7,10-tetraazacyclododecane has been investigated by means of ESR, CD and MCD in solution. X-ray studies reported separately had shown that the [CuN 4Cl] chromophores were distorted to varying extents from square pyramidal to trigonal bipyramidal geometry. The stability and rigidity of the molecular structure have enabled us to carry out a complementary study of the crystalline state and solution chemistry. The ground state Kramers doublets varied from 3d x 2− y 2 to 3d z 2 type with increasing distortion around the copper ion. The orbital sequence of the 3d 1 positive hole, d x 2− y 2 <d z 2 <d yz, xz <d xy , has been obtained for the C 4 v complexes. The 3d xy orbital is also the highest in energy for the complex with the 3d z 2 type ground state doublet. This complex exhibited superhyperfine splitting in the g z region due to the chlorine nucleus, which implies the principal z axis of the g tensor is along the CuCl bond. The sign of the copper hyperfine tensors was determined by means of Swalen's treatment. The changing values of the orbital coefficients decreasing for the 3d x 2− z 2 and increasing for the 3d z 2 , 3d xz and 3d yz in the ground state doublets have been attributed to concomitant elongation of the in-plane CuN bond and reduction of the out-of-plane CuCl bond length with the increasing distortion around the copper ions.

35Cl nuclear quadrupole resonance studies of molecular motions of ClO 3− and water diffusion in Ca(ClO 3) 2·2H 2O

A 35Cl nuclear quadrupole resonance ( 35Cl-NQR) investigation of polycrystalline Ca(ClO 3) 2·2H 2O is described. The 35Cl-NQR frequencies ( ν Q) for two resonance lines ( ν Q1 and ν Q2), the spin lattice relaxation time ( T 1Q) for ν Q2 only and the line width δν Q2 were measured in the temperature range 292–345 K, except for the frequency measured up to 455 K. The observed decrease in the resonance frequencies with increasing temperature permitted the determination of the frequencies of librations of the ClO 3 − ion about two axes perpendicular to the three-fold axis of the ion mainly responsible for this effect. The temperature dependence of the relaxation time T 1Q proved the occurrence of water diffusion and hindered rotation of ClO 3 − ions. The activation energies of these two molecular motions were determined, and their effect on the electric field gradient at the site of a chlorine nucleus was discussed. Temperature measurements of the line width δν Q2 confirmed the conclusions drawn from the analysis of T 1Q( T).

Residual dipolar splittings in, 13C MAS NMR arising from interactions with chlorine nuclei

AbstractResidual dipolar splittings in 13C cross‐polarization magic‐angle spinning spectra arising from coupling to chlorine nuclei are reported for the three chloroacetanilide isomers, using several spectrometers. At medium to high magnetic field doublets are seen for CCl carbon resonances. Perturbation theory explains the appearance of the spectra qualitatively but is inadequate quantitatively.

Finite element multiconfiguration Hartree–Fock determination of the nuclear quadrupole moments of chlorine, potassium, and calcium isotopes

The nuclear quadrupole moments of chlorine, potassium, and calcium nuclei are determined by combining calculated electric field gradients at the nucleus with the experimental nuclear quadrupole coupling constants. The electric field gradients are obtained using large-scale finite-element multiconfiguration Hartree–Fock calculations on Cl(3p5;2P3/2), K(4p; 2P3/2), K(3p53d4s;4F9/2), and Ca(3d4s;1D2). The calculated nuclear quadrupole moments are Q(35Cl)=−81.65(80) mb, Q(37Cl)=−64.35(64) mb, Q(39K)=60.1(15) mb, Q(40K) =−74.9(19) mb, Q(41K)=73.3(18) mb, Q(41Ca)=−66.5(18) mb, and Q(43Ca) =−40.8(8) mb with the estimated uncertainty given within parentheses.