Search results for "Coupling"
showing 10 items of 1862 documents
Complete Spectral Analysis of the1H NMR 16-Spin System of β-Pinene
1997
The complete analysis of the 1H NMR spectrum of β-pinene, (1S)-(-)-6,6-dimethyl-2-methylenebicyclo[3.1.1]heptane, which is of the ABCDEFGHIJX3Y3 type, is reported and earlier results are corrected. The vicinal coupling constants, 3J(H,H), are compared with the theoretical values calculated by using the Altona and co-workers’ equations for the structure derived by molecular modelling. The results were applied to the conformational analysis of β-pinene. © 1997 John Wiley & Sons, Ltd.
O Triclusters Revisited: Classical MD and Quantum Cluster Results for Glasses of Composition (Al2O3)2(SiO2)
2006
The (17)O NMR spectrum of CaAl(2)Si(2)O(8) glass shows two types of O sites that are not present in the crystalline material. One of these, with (17)O NMR parameters C(Q) = 2.3 MHz and delta = +20 ppm, has been assigned to a "tricluster" O, a local geometry in which the O is coordinated to three tetrahedrally coordinated atoms, either Al or Si. For crystalline CaAl(4)O(7), a tricluster site (with three Al linkages to O, i.e., OAl(3)) has been characterized experimentally, with a C(Q) of 2.5 MHz and a delta of about +40 ppm. Thus, a C(Q) value of 2.5 MHz or less seems to be a characteristic of such sites, although they may show a range of delta values. However, several different quantum chem…
Hot electron effects in metallic single electron components
1996
Thermalisation of single electron devices is of considerable current interest because of its fundamental and practical consequences. We present experimental evidence of the effect of electrode volume and its shape on thermal equilibration of small metallic islands for single electron tunnelling. Heat transport between the conduction electrons and the lattice in a metal is commonly accepted to obey the ∝Te5-T0/5 law at low electron and lattice temperatures,Te andT0, respectively. We have investigated the power law and found that it obeys the ∝T5 law only for the smallest islands, and in the majority of the cases considered, it rather follows a law ∝Tp, wherep<5. The thermal coupling can be i…
Conformation of the galactose ring adopted in solution and in crystalline form as determined by experimental and DFT 1H NMR and single-crystal X-ray …
2003
The solution-state conformations of various galactose derivatives were determined by comparison of the experimental (1)H-(1)H vicinal coupling constants to those calculated using density functional theory (DFT) at the B3LYP/cc-pVTZ//B3LYP/6-31G(d,p) level of theory. The agreement between the experimental and calculated vicinal coupling constants for 1,2:3,4-di-O-isopropylidene-alpha-d-galactopyranose was good, thereby confirming an (O)S(2) skew conformation for it and its derivatives on the basis of their similar observed couplings. Single-crystal X-ray analysis of 1,2:3,4-di-O-isopropylidene-6-O-(3,4,6-tri-O-acetyl-2-deoxy-2-N-phthalimido-beta-d-glucopyranosyl)-alpha-d-galactopyranose and …
One-bond 1 J (15 N,H) coupling constants at sp2 -hybridized nitrogen of Schiff bases, enaminones and similar compounds: A theoretical study
2020
1 J(15 N,H) coupling constants for enaminones and NH-forms of intramolecularly hydrogen-bonded Schiff bases as model compounds for sp2 -hybridized nitrogen atoms are evaluated using density functional theory (DFT) to find the optimal functionals and basis sets. Ammonia is used as a test molecule and its one-bond coupling constant is compared with experiment. A methylamine Schiff base of a truncated molecule of gossypol is used for checking the performance of selected B3LYP, O3LYP, PBE, BHandH, and APFD density functionals and standard, modified, and dedicated basis sets for coupling constants. Both in vacuum and in chloroform, modeled by the simple continuum model of solvent, the modified b…
Antimony-121 Mössbauer spectra of organoantimony derivatives containing Sb-Sb bonds
1994
121-Sb Mossbauer data are reported for a number of organoantimony rings and catena-stibanes. These compounds are representative of RSb(Sb)2 and R2SbSb type of coordination, and spectral parameters are compared and discussed in relation to RSbCl2 and R2SbCl systems. Although the trend in isomer shift is similar, the present compounds show slightly less negative isomer shift values together with a remarkable reduction of the quadrupolar coupling constant. A rationalization of the quadrupolar interaction in the above series of compounds appears feasible by using point charge model calculations whose results, in terms of bonding, indicate a large contribution of p-electron density along Sb-Sb b…
Radiative muon capture and the value of gP in nuclei
1990
Abstract Radiative muon capture by nuclei is analyzed by means of sum rule techniques, providing a total photon yield calculated with RPA precision. The measured yields relative to the ordinary muon capture rate are well reproduced for the nuclei 12C, 16O and 40Ca using a value of the pseudoscalar weak coupling constant gP enhanced by only 25% with respect to its canonical value. Therefore, the large renormalization of gP claimed up to now must be reconsidered.
Nuclear Spins of the IsomersHg191m−185mDetermined by On-Line Quantum-Beat Spectroscopy
1979
The nuclear spins of the very neutron-deficient $^{191m\ensuremath{-}185m}\mathrm{Hg}$ isomers were measured on line at the mass separator ISO LIDE at CERN using pulsed-laser excitation and observation of the time-resolved quantum beats from selected hyperfine-structure states. The spins of these isomers are with $I=\frac{13}{2}$ equal to those of the long-lived isomers $^{199m\ensuremath{-}193m}\mathrm{Hg}$ already known. The persistence of this spin value for eight isomers is explained by the model of rotation-aligned coupling.
Infrared renormalization of two-loop integrals and the chiral expansion of the nucleon mass
2007
We describe details of the renormalization of two-loop integrals relevant to the calculation of the nucleon mass in the framework of manifestly Lorentz-invariant chiral perturbation theory using infrared renormalization. It is shown that the renormalization can be performed while preserving all relevant symmetries, in particular chiral symmetry, and that renormalized diagrams respect the standard power counting rules. As an application we calculate the chiral expansion of the nucleon mass to order O(q^6).
Contribution of the $a_1$ meson to the axial nucleon-to-$\Delta$ transition form factors
2018
We analyze the low-$Q^2$ behavior of the axial form factor $G_A(Q^2)$, the induced pseudoscalar form factor $G_P(Q^2)$, and the axial nucleon-to-$\Delta$ transition form factors $C^A_5(Q^2)$ and $C^A_6(Q^2)$. Building on the results of chiral perturbation theory, we first discuss $G_A(Q^2)$ in a chiral effective-Lagrangian model including the $a_1$ meson and determine the relevant coupling parameters from a fit to experimental data. With this information, the form factor $G_P(Q^2)$ can be predicted. For the determination of the transition form factor $C^A_5(Q^2)$ we make use of an SU(6) spin-flavor quark-model relation to fix two coupling constants such that only one free parameter is left.…