Determination of volatiles in spirits using combined stationary phases in capillary GC

Summary The analysis of spirits with a single stationary phase is still an unsolved problem; the two amyl alcohols, ethyl acetate and acetal are not separated on a polar column, methanol and acetaldehyde coelute from an apolar column. Trials with coupled columns of different polarities showed that optimum results were obtained with a 40 m capillary column, comprising 6 m of Carbowax 20 M, 12 m of 1:1 Carbowax 20M:OV1 mixture and 30 m of PS 264. Best results were achieved when a 1 m retention gap was used, injecting a small amount of sample and using a 7 cm syringe needle.     

Effects of the reaction environment on gas-phase proton-induced nucleophilic displacement at saturated carbon1

The H₂O and D₂O chemical ionization (CI) mass spectra of selected methylhalides(CH₃X, XF, CI) have been investigated at source temperatures from 330 to 500°K, and at total pressures from 01 to 1.1 Torr Hydronium (H₃O⁺) ions, the reactant species formed that predominates in our source under these conditions, were found to promote a gas-phase nucleophilic substitution on the halogenated substrate by H₂O, leading to CH₃OH₂⁺ (H₂O)_n (n = 0,1,2) ions. Occurrence of these substitution reactions, which are prevented under ICR conditions, provides direct evidence for contrasting ion reactivities under different experimental conditions, mainly due to the profound influence of the reaction environment on the formation of collision-stabilized intermediate species.     

Highly sintered nickel oxide: surface morphology and FTIR investigation of CO adsorbed at low temperature

The monolayer of CO molecules adsorbed at low temperature on highly sintered nickel oxide, gives rise to a very symmetric IR absorption band at 2136 cm⁻¹ (θ_max) with a full-width at half-maximum (FWHM) of 3.7 cm⁻¹. This band shifts to higher frequenc upon decreasing the coverage, reaching the 2152 cm⁻¹ value for θ→0. The observed shift is due to changes in the lateral interactions (dynamic and static) among the adsorbed molecules. The observed spectral simplicity implies that most of the adsorbed CO molecules occupy crystallographically identical sites with a similar environment. Moreover, the remarkably small half-width indicates that inhomogeneous broadening effects, due to surface defects, are very small and that NiO microcrystals behave as single crystals. The morphology of microcrystals has been studied by SEM, AFM and HRTEM techniques: it was concluded that the surface termination of the sample is mainly represented by the (100) and (111) faces.     

MS Xα and LCAO Xα calculations of ionization potentials. A comparison with Koopmans' theorem and accurate calculations

Ionization potentials of small molecules are calculated by the MS Xα and LCAO Xα methods. The results are compared with the experimental values and the results of previous accurate calculations. The Xα method proves to be rather accurate and potentially superior to the HF method. Indication is found of a possible failure of the method in the fluoromethanes. The limitation of the MS Xα method is discussed.     

Effect of the group IV elements on the Π anion and cation states of thiophene and furan determined by means of ETS and UPS

The electron-transmission and He(I) photoelectron spectra of Si(CH₃)₃, Sn(CH₃)₃ and CH₂Si(CH₃)₃ derivatives of thiophene and furan have been recorded. The first two substituents perturb the energies of the outer filled π orbitals and of the empty π* orbitals in opposite directions, causing a reduction of the HOMO/LUMO energy separation. The stabilization experienced by the π* MO's depends on their wavefunction coefficients at the site of substitution, and is attributed to interaction with low-lying empty orbitals of the substituent groups. The relatively small size (～ 0.4 eV) of this effect on the unoccupied ring MO's suggests that it should not appreciably affect the energy of the filled MO's.The strong conjugation between the π* unoccupied orbital of the nitro group and those of thiophene has also been investigated.     

A PAM-PPM signalling format in optical fibre digital communications

A combined pulse amplitude modulation (PAM) and pulse position modulation (PPM) technique is proposed and investigated as a feasible solution of the problem of line encoding in optical fibre communication systems. The basic idea is that of exploiting PAM and PPM jointly, to give rise to three different waveforms in one signalling period, without resorting to more than two signal levels. Some evaluations of the behaviour of this signalling format are reported in terms of coding efficiency, spectral density, timing information, and error probability. Alternative receiving schemes are also devised to improve system performance.     

Surface relaxation and reconstruction in diamond-like crystals

The MNDO semiempirical method has been used to study the structure of the (111) surface of diamond-like crystals employing two model clusters. Numerical results are in agreement with previous computations for the small X₄H₉ clusters and become very similar to experimental data when employing the larger X₉H₁₅ clusters. These latter clusters allow also the study of surface reconstruction. Our results suggest that the Haneman model of 2 × 1 reconstruction could be equally valid for silicon and diamond, but in the latter case the difference in vertical shifts is too small to be experimentally observed.     

A hollow cathode for high-resolution optogalvanic spectroscopy: Application to uranium

Summary We report the design criteria and performance characteristics of a hollow-cathode tube developed especially for high-resolution Doppler-free laser spectroscopy. It is simple to construct and is easily demountable. Narrow homogeneous line widths of refractory and highly reactive-element transitions have been observed by applying intermodulated detection scheme. To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.