6Li and 7li solid-state NMR spectroscopy of nitrogen ceramic phases

Two nitrogen ceramic phases, the oxynitride LiSiON and the nitride LiSi2N3, have been studied by 6Li and 7Li NMR. Magic angle spinning (MAS) NMR experiments have been carried out at two magnetic field strengths (7.05 and 14.1 T). The spectra give evidence of the relative effects of the quadrupolar and chemical shift interactions. The electric field gradient tensor of both phases has been determined accurately by iterative fitting of the 6Li and 7Li MAS NMR line shapes at the two magnetic field strengths. Due to the fact that for 7Li the quadrupolar interaction is much larger than the chemical shift interaction, it is shown that neither the small chemical shift anisotropy nor the relative orientation of the two interaction tensors can be determined accurately by 7Li MAS NMR. For 6Li, the two interactions are comparable and the value of these parameters obtained from the fits of the 6Li experimental MAS line shapes are therefore much more reliable.     

Relative rate measurements of some reactions of hydroxyl radicals with alkanes studied under atmospheric conditions

A flow system has been developed to study relative rate coefficients of hydroxyl radicals reacting with alkanes under conditions relating to tropospheric chemistry. Relative Arrhenius parameters have been measured over the temperature range 243–328 K for pairs of alkanes from a list consisting of n-butane, 2-methylpropane, n-pentane, n-hexane, 2,2- and 2,3-dimethylbutane, 2,3,3-trimethylbutane, and 2,3,4-trimethylpentane. The results have been incorporated into a Structure-Activity Relation for hydroxylalkane reactions which leads to the following group rate coefficients for a temperature range of 240–500 K.      

The charge distribution in chromium(III) and iron(III) hexafluoride

Semi-empirical molecular orbital calculations were performed for CrF^3?₆ and FeF^3?₆. The method of calculation is derived from the HF SCF equations using approximations appropriate to the highly ionic transition metal halides. The results of these calculations are shown to be in better agreement than previous semis-empirical calculations with X-ray emission line shifts and atom charges and populations estimated from these shifts.     

Wide-band interferometric tuning of a multiatmosphere CO2 laser

We describe the operating characteristics of a compact, frequency tunable, electron-beam-controlled, 15 atmosphere CO₂ laser. Two intracavity Fabry-Perot etalons have been used to obtain laser line narrowing and continuous tuning within the 10.4 μm and 9.4μm bands of the CO₂ gain spectrum. The laser output consists of a 100 nsec pulse (fwhm) with energy up to 100 mJ. The overall laser tuning range is 70 cm^-1 and we have measured a laser linewidth of 0.03 cm^-1.     

Nuclear magnetic resonance study of In115 in B2-type PdIn

NMR measurements on In¹¹⁵ in B2-type PdIn from RT to 4.2°K are reported The low Knight shift is attributed to a reduction of the amount of s- character in wave functions at the In sites and not the density of states at the the Fermi level. The existence of a localized moment is considered.     

Librational anharmonicity in solid α-N2

The effects of librational anharmonicity in solid α-N₂ are studied. Anharmonic frequencies are obtained using a boson representation for torsional motion. Two-libron and (one stretch + one libron) processes observed via Raman spectroscopy are discussed. Cubic libron-phonon interactions are shown to account for anomalies in the widths of the optical phonons as observed in infrared absorption.