N nuclear quadrupole resonance of picolinic,nicotinic, isonicotinic and dinicotinic acids

The ¹⁴N nuclear quadrupole resonance (NQR) quadrupole coupling tensors of picolinic, nicotinic, isonicotinic and dinicotinic acids have been determined. Two different ¹⁴N quadrupole coupling constants 1007 kHz and 4159 kHz have been observed for picolinic acid demonstrating the presence of both protonated and non-protonated nitrogen atoms in this system in the solid. Only one set of non-protonated ¹⁴N NQR lines has been observed in other pyridinecarboxylic acids demonstrating the absence of the protonated zwitter ion forms observed in picolinic acid. The non-protonated ¹⁴N quadrupole coupling constant is the highest for the non-protonated nitrogen in picolinic acid and decreases to 3774 kHz in nicotinic acid and 3570 kHz in isonicotinic acid. It is the lowest in dinicotinic acid where the corresponding ¹⁴N quadrupole coupling constant is 2794 kHz. The observed anomalous decrease in the ¹⁴N quadrupole coupling constant of dinicotinic acid with decreasing temperature is tentatively explained as reflecting the increase in the residence time of the N–H?O bonded proton in the potential well close to the nitrogen.     

Ion source emittance influence on the transmission of a quadrupole operated in the second stability region

The variation of transmission (T) with resolution (R) has been calculated for a quadrupole mass filter operated in the second stability region with Mathieu parameters q=7.547 and a=0 to 0.02995. The fringing fields at the entrance to the quadrupole, which can be strongly defocusing, and which can dramatically reduce the acceptance, have been included in the calculation. Even in the absence of fringing fields, at a resolution of 10,000 the acceptance in the x and y directions is less than 2 × 10^?4 πr ₀ ⁴ f ², which is about 10^?3 of the acceptance in the first stability region at low resolution. Because the source emittance can strongly effect the T(R) behavior, the calculation of ion transmission has been done for two source emittances that correspond to different degrees of focusing of ions into the quadrupole. The T(R) characteristics for two realistic source emittances give behavior markedly different from the decrease in acceptance with increasing resolution which previously has been used as a measure of the quadrupole transmission. Comparisons of the calculated transmission losses with increasing resolution to earlier experimental results obtained with an inductively coupled plasma source show good agreement provided an emittance which corresponds to ions being tightly focused into the quadrupole is used. The calculation demonstrates that up to a resolution at half height of 7000 in the experiment, the transmission losses were a result of the decreasing quadrupole acceptance. At higher resolution the experimental transmission was limited by either the residence time of the ions in the quadrupole or the rod quality. It is also shown that the strong defocusing effects of the fringing fields at the entrance of the quadrupole can be largely overcome by accelerating the ions through these fields and then decelerating the ions in the quadrupole.     

Calculation of the electric susceptibilities of the helium atom

We calculated the static and the dynamic dipole polarizabilities and the static quadrupole polarizability of the helium atom. The results are α = 0.2070 × 10^?24 cm³ for the static dipole polarizability and γ₄ = 0.1038 × 10^?40 cm⁵ for the static quadrupole polarizability.     

83 Kr Nuclear quadrupole coupling in KrHF: evidence for charge transfer

The ⁸³Kr nuclear quadrupole coupling constant in KrHF has been measured to be x = 10.227(71) MHz. Using the known ⁸³Kr nuclear quadrupole moment, the field gradient at the Kr nucleus is evaluated and interpreted in terms of charge transfer in the weak Kr-HF van der Waals bond. Rotational assignments are reported for ⁸²Kr, ⁸³Kr, ⁸⁴Kr, and ⁸⁶Kr isotopic KrHF.     

Next-nearest neighbor effects in the Mössbauer spectra of (Cr,Al) spinels

Fe²⁺T-site quadrupole splitting observed in the Mössbauer spectra of synthetic chromite-hercynite spinels (Fe(Cr_1?xAl_x)₂O₄, with x = 0 to 1.5) is systematically related to the substitution of octahedrally coordinated cations in the next-nearest neighbor coordination sphere. Conditions of synthesis include dry reagents contained in a stainless-steel crucible and enclosed in an evacuated silica-glass tube, held at 1250°C for up to 4 days. A simple singlet spectrum for FeCr₂O₄ changes with progressive Al substitution into a broadened doublet spectrum, with quadrupole splitting of 1.28 mm/sec and line half-width of 0.82 mm/sec, for FeCrAlO₄. Partial quadrupole splitting theory is used to calculate the quadrupole splittings for individual next-nearest neighbor configurations. Bulk quadrupole splitting is calculated relative to the statistical distribution of possible next-nearest neighbor configurations. Calculated quadrupole splittings are in good agreement with those obtained for unconstrained two-peak fits, at room temperature and at low and high temperature. Also, predicted spectral details are resolved in low temperature spectra. The local site distortion responsible for the quadrupole splitting appears to be associated with spatial accommodation of substituent Al³⁺ cations.     

The rotational spectrum,nuclear spin—spin coupling,nuclear quadrupole coupling,and molecular structure of KrHF

Rotational spectra have been assigned for the ⁸²Kr, ⁸³Kr, ⁸⁴Kr, and ⁸⁶Kr isotopic species of the KrHF and KrDF van der Waals molecules by using pulsed microwave Fourier transform spectroscopy in a Fabry—Perot cavity with a pulsed supersonic nozzle molecular source. The rotational, centrifugal distortion, nuclear spin—spin, and nuclear quadrupole coupling constants are used to determine the structure and obtain intramolecular potential binding information. The ⁸³Kr nuclear quadrupole coupling constants are 10.28 ± 0.08 MHz and 13.83 ± 0.13 MHz for KrHF and KrDF respectively. The electric field gradient at the krypton nucleus is calculated from the coupling constant and the known nuclear quadrupole moment and explained by Sternheimer shielding and formation of the van der Waals bond. There is a negligible charge transfer in the KrHF bond.     

The microwave spectrum of chloroacetyl chloride

The microwave spectrum, rotational constants and centrifugal distortion parameters for CH₂³⁵ClCO³⁵Cl are reported. The nuclear quadrupole coupling constants of the two non-equivalent Cl atoms were determined from partially resolved quadrupole splittings. The molecule is planar in the conformation studied here and both Cl atoms occupy the trans position as shown from their substitution coordinates.     

A novel quadrupole,quistor, quadrupole tandem mass spectrometer

A quadrupole, quistor, quadrupole tandem mass spectrometer allowing selected ion/selected molecule reactions was built. The quistor will be used as a reaction chamber for the study of organic ion-molecule reactions. Ions are generated in a differentially pumped ion source, quadrupole mass selected and injected into the quistor. The ions are trapped in the quistor by the combined action of a deceleration lens, the presence of helium buffer gas and the quistor RF field. As a first test of the performance of the instrument, the reaction rate constant of the reaction of O₂⁺˙ with methane was measured to be 5 × 10^?12 cm³s^?1. This is in good agreement with literature values, indicating that the ions are near thermal equilibrium after a few milliseconds of trapping time.     

Centrifugal distortion and oxygen-17 quadrupole coupling in ethylene oxide

The microwave spectrum of ethylene oxide has been reinvestigated to determine its quartic centrifugal distortion constants and the quadrupole coupling constants of the ¹⁷O species. The measurements of the quadrupole structure were done in natural isotopic abundance (0.037%) using a computer coupled spectrograph.     

Computer simulations of 2H MAS NMR spinning sideband spectra

The quadrupole coupling constant and asymmetry parameter of a ²H MAS NMR spectrum can be derived by computer simulations of the spinning sideband pattern. Off angle spinning causes complex lineshapes which can be used to find approximate quadrupole parameters and to determine more accurately the asymmetry.     

Correlation of nitrogen-14 nuclear quadrupole resonance data in sulfanilamides with the in vitro activities

Several sulfanilamide-type compounds in their solid state have been investigated by the ¹⁴N nuclear quadrupole resonance (NQR) technique. The electron distributions at the sites of the nitrogen atoms, calculated by the Townes and Dailey theory, indicate a significant correlation between the quadrupole coupling constant for the primary amino nitrogen (N⁴), which is a measure of the (π-σ) electron density at N⁴, and the in vitro bacteriostatic activity of the sulfanilamides.     

Microwave spectra of [15n] and [13c] pyridines,quadrupole coupling constants,dipole moment and molecular structure of pyridine

The microwave spectra of two ring-substituted species of pyridine have been remeasured, and the spectra of the two remaining species investigated and assigned.¹⁴N quadrupole coupling splittings were analyzed and used to determine the quadrupole coupling constants, while the derived center frequencies were fitted to give improved values for the rotational constants.A complete substitution structure can now be presented.The dipole moment of pyridine was redetermined from Stark measurements in the spectrum of [¹⁵N]pyridine.     

63Cu and 31P endor study of Tetra-n-Butylammonium-(Maleonitriledithiolato) (Monoethyldithiophosphato) cuprate(II)/Nickelate(II) (n-Bu4N)[Cu/Ni(mnt)(H(et)dtp)]

The ⁶³Cu quadrupole, the ⁶³Cu hyperfine and ³¹P hyperfine coupling tensors of the mixed-ligand chelate (n-Bu₄N)[⁶³Cu(mnt)(H(et)dtp)] doped into the corresponding nickel complex have been measured by ENDOR spectroscopy. Conclusion are drawn concerning the symmetry of the Cu complex. The ⁶³Cu quadrupole tensors and the ³¹P hyperfine tensors can be understood assuming a “transannular Cu 3d_itx2 -_ity2-P 3s overlap”.     

Possibilities for Energy Transport into a Radio-Frequency Quadrupole by a Shifted Supersonic Gas Jet. Part II. Accumulation and Heating of Ions

The aim of this work was the assessment of the ability of a supersonic jet to accumulate sufficiently dense ion clouds inside the quadrupole, the ion cloud being “heated” to a relatively high temperature under a relatively low density of the residual gas (pressure lower than 10^–4 Torr). Kinetic measurements gave an estimate of the number of accumulated ions at the beginning of the quadrupole of about 2 × 10⁷ and their internal temperature of 6000 K.     

CI study of rovibrational dependence of nuclear quadrupole coupling constants of all isotopic variants of OH+ in the X3Σ− state

The ¹⁷O and ²H quadrupole coupling constants of rovibrational levels of ¹⁷O¹H⁺, ¹⁷O²H⁺, and ¹⁶O²H⁺ in their X³Σ⁻ state have been calculated from molecular wave functions that explicitly describe nuclear motion. The ¹⁷O quadrupole coupling is predicted to be strong and its vibrational dependence differs from that known for other nuclei A in the first-row hydrides AH or AH⁺. The deuterium coupling in ¹⁷O²H⁺ and ¹⁶O²H⁺ is found to be weak and its behavior is similar to that of other first-row hydrides. The change with rotational excitation is unimportant. The quadrupole hyperfine patterns of ¹⁷O²H⁺ in its ground state are dominated by the strong oxygen coupling. © 1996 John Wiley & Sons, Inc.     

Theoretical description of nuclear quadrupole coupling in light diatomic molecules

A practical procedure for calculation of nuclear quadrupole coupling constants for light diatomic molecules is discussed. The procedure is based on a molecular wave function that explicitly describes nuclear motion. The approach is capable of yielding quadrupole coupling constants for excited rovibrational levels of diatomic molecules in their ground and excited electronic states. An application of the procedure to the X¹Σ⁺_g and B¹Σ⁺_u states of HD and D₂ is presented.     

Monte Carlo simulation of liquid Br2: Test of an effective hamiltoniain

Monte Carlo simulations for the structure of a fluid of molecules interacting with a pair potential having one Lennard- Jones center plus a quadrupole interaction is reported. The numerical experiments are compared with an approximation method previously suggested and with experimental results for the liquid Br₂ structure. This effective pair potential turns out to be unable to reproduce the Br₂ structure while the approximation method is only useful for quadrupole moments less than 1.2 × 10^?40 C m².     

Mössbauer effect studies on sodium hexa/carboxylato/ ferrates/III/

Mössbauer spectra of a series of the complexes of the type Na₃[Fe/RCOO/₆]xH₂O /R=H, CH₃, C₂H₅, C₆H₅/ has been recorded at 298±2 K. All display a quadrupole doublet with isomer shift and quadrupole splitting values in agreement with high spin iron/III/ octahedral geometry. The quadrupole splitting show an increasing trend with increasing polarizability of the substituent anion /RCOO^–/. A linear correlation between quadrupole splitting values and the /Fe–O/ stretching frequencies has also been observed.     

Author index to volume 91

The refocusing of a molecular beam of CaBr X²Σ⁺ by an electric quadrupole is investigated. The enhancement by electric deflection of the intensities of lines originating from levels of low J in the fluorescence excitation spectrum of CaBr B²Σ⁺ ?X²Σ⁺ is shown to be a useful technique of line assignment in a dense electronic band system. It is also found that the hyperfine levels are not transmitted equally through the quadrupole; for f levels, the hyperfine populations are actually reversed. A qualitative explanation, based on the correlation of zero-field hyperfine levels with high-field states, is given.     

Calculation of the 14N and 2H quadrupole coupling tensor in trimeric imidazole

The ¹⁴N and ²H quadrupole coupling tensors at both nitrogen and at all hydrogen sites, have been calculated by ab initio SCF MO methods, in a trimeric imidazole molecule having the geometry found in the solid state. The ¹⁴N changes produced at N(1)H by hydrogen bonding are correctly reproduced to a noteworthy degree of precision, as is the ²H quadrupole interaction at the same site. The changes in the values of the three principal components of the tensor, which have been inferred from NQR measurements when imidazole passes from the gas to the solid state, are supported by the calculations, both for N(1)H and N(3).