Ammonia: The molecule for establishing N and N absolute shielding scales and a source of information on nuclear magnetic moments.

Multinuclear Nuclear Magnetic Resonance (NMR) studies of the gaseous mixtures He/NH and He/NH are reported. Precise analysis of the He, N, N, and H resonance frequencies show a linear dependence on the gas density. Extrapolation of these results to the zero-pressure limit gives ν(H), ν(N), and ν(N) resonance frequencies of the isolated ammonia molecule at 300 K.

Absolute C nuclear magnetic shielding of simple isolated molecules from gas phase measurements.

The new experimental value of C absolute shielding constant in an isolated CO molecule was evaluated from the C and He gas phase NMR measurements performed for He/CO mixtures. An absolute shielding constant (CO)= 0.80(90) ppm was previously formally established for this reference molecule with uncertainty but much higher precision than ever before.

Deuterium isotope effects on O nuclear shielding in a single water molecule from NMR gas phase measurements.

Small amounts of enriched H217O and 3He in gaseous mixtures with CH3F and CF3H were studied using 1H, 3He and 17O NMR spectroscopy. After extrapolation of the results to the zero density limit, the shielding constants in the isolated molecules: H217O, H17OD and D217O were precisely determined. The isotope effects are as follows: 2Δ1H(HOH, HOD) = -0.

H, C and Si magnetic shielding in gaseous and liquid tetramethylsilane.

Tetramethylsilane (TMS) is well-known as a reference standard of H, C and Si NMR chemical shifts. In the present study, we have observed TMS molecules in gaseous and liquid solutions. In the gas phase, the shielding parameters of TMS are monitored as the functions of density when xenon and krypton are applied as the buffer gases.

Gas-phase Ne NMR studies and the nuclear magnetic dipole moment of neon-21.

Gas-phase Ne nuclear magnetic resonance spectra were measured at the natural abundance of Ne isotope for samples consisting of pressurized neon up to 60 bar at room temperature and applying the magnetic field of the strength B = 11.7574 T. It showed that the nuclear magnetic resonance frequency is linearly dependent on the density of gaseous neon.

O and H NMR spectral parameters in isolated water molecules.

Small amounts of water enriched in oxygen-17 were studied by 17O and 1H NMR in binary gaseous mixtures with Xe, Kr, CHF3 and CH3F and CO2. The distinct linear dependences of 17O and 1H chemical shifts and 1J(17O,1H) spin-spin coupling on the density of every gas solvent were measured. After the extrapolation of experimental results to zero density the relevant parameters in the isolated H217O molecule were determined.

NMR absolute shielding scale and nuclear magnetic dipole moment of (207)Pb.

An absolute shielding scale is proposed for (207)Pb nuclear magnetic resonance (NMR) spectroscopy. It is based on ab initio calculations performed on an isolated tetramethyllead Pb(CH3)4 molecule and the assignment of the experimental resonance frequency from the gas-phase NMR spectra of Pb(CH3)4, extrapolated to zero density of the buffer gas to obtain the result for an isolated molecule. The computed (207)Pb shielding constant is 10 790 ppm for the isolated molecule, leading to a shielding of 10799.

(129) Xe and (131) Xe nuclear magnetic dipole moments from gas phase NMR spectra.

(3) He, (129) Xe and (131) Xe NMR measurements of resonance frequencies in the magnetic field B0=11.7586 T in different gas phase mixtures have been reported. Precise radiofrequency values were extrapolated to the zero gas pressure limit.

The NMR spin-spin coupling constant ¹J(³¹P,¹H) in an isolated PH₃ molecule.

We present new experimental and calculated values of the indirect spin-spin coupling constant (1)J((31)P,(1)H) in the PH3 molecule. The line shape analysis of (1)H and (31)P gas-phase NMR spectra recorded at several densities of PH3, followed by extrapolation of the results to the zero-density limit, gives 176.18(2) Hz as the experimental value at 300 K.

¹J(CH) couplings in Group 14/IVA tetramethyls from the gas-phase NMR and DFT structural study: a search for the best computational protocol.

Four tetramethyl compounds EMe4 (E = C, Si, Ge, and Pb) were studied by high-resolution NMR spectroscopy in gaseous and liquid states at 300 K. Extrapolation of experimental vapor-phase C-H J-couplings to a zero-pressure limit permitted determining the (1)J(0,CH)s in methyl groups of their nearly isolated molecules. Theoretical predictions of the latter NMR parameters were also performed in a locally dense basis sets/pseudopotential (Sn, Pb) approach, by applying a few DFT methods pre-selected in calculations of other gas-phase molecular properties of all these species and SnMe4 (bond lengths, C-H stretching IR vibrations).

(83)Kr nuclear magnetic moment in terms of that of (3)He.

High resolution NMR spectroscopy was applied to precisely determine the (83)Kr nuclear magnetic dipole moment on the basis of new results available for nuclear magnetic shielding in krypton and helium-3 atoms. Small amounts of (3)He as the solutes and (83)Kr as the buffer gas were observed in (3)He and (83)Kr NMR spectra at the constant external field, B0 = 11.7578 T.

17O and 33S nuclear magnetic shielding of sulfur trioxides from the experimental measurements and theoretical calculations.

In a recent (17)O NMR spectra of liquid sulfur trioxide, several unexpected peaks appeared with the temperature-dependent integrated peak ratio. In order to interpret NMR spectra and assign peaks to possible molecular structures, the theoretical quantum mechanical density functional theory and Møller-Plesset second-order perturbation theory calculations were performed. It is suggested that in the liquid sulfur trioxide, apart from monomeric SO3, a significant amount of (SO3)3 cyclic trimers should appear.

Spin-rotation and NMR shielding constants in HCl.

The spin-rotation and nuclear magnetic shielding constants are analysed for both nuclei in the HCl molecule. Nonrelativistic ab initio calculations at the CCSD(T) level of approximation show that it is essential to include relativistic effects to obtain spin-rotation constants consistent with accurate experimental data. Our best estimates for the spin-rotation constants of (1)H(35)Cl are CCl = -53.

Nuclear magnetic shielding for hydrogen in selected isolated molecules.

We present the results of gas-phase NMR measurements designed to yield a new experimental value for the absolute (1)H magnetic shielding for an isolated hydrogen molecule and its deuterium isotopomers. The results are based on the original method of direct shielding measurements (Jackowski et al., 2010) and the density dependence of (1)H, (2)H, and (3)He NMR frequencies for molecular hydrogen and atomic helium-3.

NMR shielding constants in PH3, absolute shielding scale, and the nuclear magnetic moment of 31P.

Ab initio values of the absolute shielding constants of phosphorus and hydrogen in PH(3) were determined, and their accuracy is discussed. In particular, we analyzed the relativistic corrections to nuclear magnetic resonance (NMR) shielding constants, comparing the constants computed using the four-component Dirac-Hartree-Fock approach, the four-component density functional theory (DFT), and the Breit-Pauli perturbation theory (BPPT) with nonrelativistic Hartree-Fock or DFT reference functions. For the equilibrium geometry, we obtained σ(P) = 624.

(13)C shielding scale for MAS NMR spectroscopy.

We have performed the direct measurements of (13)C magnetic shielding for pure liquid TMS, solution of 1% TMS in CDCl3 and solid fullerene. The measurements were carried out in spherical ampoules exploring the relation between the resonance frequencies, shielding constants and magnetic moments of (13)C and (3)He nuclei. Next the (13)C shielding constants of glycine, hexamethylbenzene and adamantane were established on the basis of appropriate chemical shifts measured in the solid state.

Temperature dependence of the (1)J((11)B(19)F) spin-spin coupling in BF(3) molecule.

The (1)J((11)B(19)F) spin-spin coupling of gaseous BF(3) was observed in (11)B NMR spectra as a function of density in a wide range of temperatures. Following the extrapolation of the measured values to the zero-density limit, the coupling constant free from intermolecular effects (1)J(0)((11)B(19)F) was obtained for each temperature. In contrast to previous investigations, the final results indicate a nonlinear dependence of (1)J(0)((11)B(19)F) on temperature.

NMR shielding constants in BF(3) and magnetic dipole moments of (11)B and (10)B nuclei.

Gas-phase NMR spectra of (11)B, (10)B, and (19)F in BF(3) are reported, and high-level ab initio calculations of the corresponding NMR shielding constants are described. Extrapolation of the measured resonance frequencies to the zero-density limit ensures that the results correspond to the ab initio values for an isolated molecule. Simultaneous measurements of (3)He resonance frequencies and application of the calculated shielding constants allow us to determine improved values of the nuclear magnetic dipole moments of (11)B and (10)B.