Signs Of Quadrupole Coupling Constants Research Articles

Signs of deuteron quadrupole coupling constants from COSY-2D spectra of solids

It is shown how the signs of the quadrupole coupling constants (QCCs) of deuterons can be determined from the multiplet structures of the cross peaks in COSY-2D spectra of deuterons in molecular crystals or any other ordered sample. Multiplets arise as a result of dipolar couplings between pairs of deuterons. The 21) multiplet of a cross peak of a dipolar-coupled pair of deuterons consists of a 3 × 3 array of component lines. If the mixing pulse of the COSY sequence is a 90° pulse the multiplet is insensitive to the signs of the deuteron QCCs. If, however, the mixing pulse is a 54°44′ pulse only four of the nine components are strong. These are located in one of the four corners of the 3 × 3 array. In which comer of the 3 × 3 array the four strong peaks appear depends on the relative signs of the dipolar and quadrupolar splittings D, Δω Q1 and Δω Q2. This can be used as a fingerprint for the relative signs of D, D, Δω Q1 and Δω Q2. The experimental conditions of the procedure are explored in an experiment on a single crystal of fully deuterated potassium oxalate monohydrate.

Sign of the electric field gradient at 57Fe nuclei in Eu 3Sc 2Fe 3O 12 garnet

The 57Fe Mössbauer effect in conjunction with an external magnetic field H ext has been used to measure the signs of quadrupole coupling constants Δ at the octahedral ( a) and tetrahedral ( d) iron sites in the Eu 3Sc 2Fe 3O 12 garnet. It is shown that application of H ext to the sample at temperatures T above the Néel temperature T N slows down the relaxation effects, whose influence on the spectra depends upon the temperature difference T-T N . By comparing a spectrum measured at 203.0 K and in H ext=62.4 kOe with theoretical spectra computed for different combinations of Δ( a), Δ( d) signs, it is concluded that Δ( d) is negative. The sign of Δ( a) could not be determined.

Deuteron NMR on single crystals. EFGs, signs of quadrupole coupling constants, and assignment of σ tensors in malonic acid

The high-field NMR of two dipolar-coupled deuterons experiencing different EFGs is investigated theoretically and shown to be solvable analytically. The determination of the signs of quadrupole coupling constants from the spectral appearance is discussed. Room-temperature FT deuteron spectra of deuterated crystals of malonic acid were recorded at 54.7 MHz. The dipolar fine structure resulting from the coupling of the deuterons of the CD 2 group could be resolved. From the rotation patterns of the line splittings, the EFGs at the sites of the four inequivalent deuterons are determined and compared with the previous work of Derbyshire et al.. The results confirm the conclusion, drawn in a previous paper on the proton NMR of malonic acid, that the methylene deuteron internuclear vector and the normal of the CCC backbone of the molecule subtend an angle of about 6°. The signs of the quadrupole coupling constants of the methylene deuterons are shown to be positive. The correlation of chemical shifts with quadrupole splittings allowed to assign directly the chemical shift tensors measured previously by multiple-pulse proton NMR to the methylene hydrogen sites.

Signs of quadrupole coupling constants for the tin(IV) adducts with acetonitrile, triethylphosphine, and triethylarsine

The signs of the quadrupole coupling constants are positive for cis-SnCl4,2MeCN, trans-SnCl4,2PEt3, and trans-SnCl4,2AsEt3 and this is consistent with the order of bond polarity Sn–N (sp-hybridized) > Sn–Cl > Sn–P or Sn–As.