Some analytical properties of the dilated SCF Equations

The self-consistent field (SCF ) equations for many-electron systems, suitable within the complex-coordinate method, are derived. The formulation is based on a general bivariational theorem for non-Hermitian operators, with an emphasis on the analytic structure invoked by the complex dilation of the total Hamiltonian. The dilation structure of the resulting SCF equations is stressed and the concomitant analytical properties are discussed. The solutions are classified with respect to these properties, and interpreted in terms of a general form of the symmetry dilemma. The role of the dilated SCF equations for resonance calculations is discussed.     

Pyrene measurements in sooting low pressure methane flames by jet-cooled laser-induced fluorescence

This paper presents in detail the study we carried out concerning the pyrene measurement by jet-cooled laser-induced fluorescence (JCLIF) in different sooting low pressure methane flames. The aim of this paper is both to demonstrate the potentialities of this technique for the measurement of such moderately sized polycyclic aromatic hydrocarbons under sooting flame conditions and to provide new experimental data for the understanding and the development of chemical models of the soot formation processes. Several concentration profiles of pyrene measured in different sooting flame (various pressure and equivalence ratio) are presented. The validation of the JCLIF method for pyrene measurements is explained in detail as well as the calibration procedure, based on the standard addition method, which has been implemented for the quantification of the concentration profiles. Sensitivity lower than 1 ppb was obtained for the measurement of this species under sooting flame conditions.     

Midinfrared polarization spectroscopy of OH and hot water in low pressure lean premixed flames

The application of midinfrared polarization spectroscopy (mid-IRPS) is demonstrated for sensitive detection of minor molecular species in combustion environments by probing rovibrational transitions. High resolution mid-IRPS spectra of low pressure flames were obtained in the spectral range around 3 microm. Rotational lines of the fundamental vibrational band of the hydroxyl radical (OH) were fully resolved and properly assigned among the abundant hot water lines in the flame mid-IRPS spectra. The high signal-to-noise ratio of the recorded OH lines indicates the feasibility of sensitive mid-IRPS OH detection. This constitutes, to the best of our knowledge, the first reported OH flame detection in the midinfrared spectral range. A simulation of hot water mid-IRPS lines with molecular parameters extracted from the HITRAN/HITEMP database was performed and compared with the observed flame spectra. The proper prediction of the hot water lines may help to clarify the potential spectral interferences associated with minor species measurements.     

Some unexpected interferences in flames

A series of interferences has been observed in emission and absorption for rare earth elements in the nitrous oxide-acetylene flame and for some first row transition elements with air and acetylene. Signal changes, mostly suppressions, are observed at low (ppm) concomitant levels with the degree of interference consistently showing an abrupt slope change at mole ratios of concomitant to analyte element of between 1-1 and 2-1. The effects are observed for high boiling, oxygen containing mineral acids and for many organic compounds which contain oxygen and which decompose instead of vaporizing when heated. Some non-volatile, nitrogen containing compounds also give suppressions but here the behavior is less consistent. The effects are very sensitive to flame richness and often can be overcome by proper fuel to oxidant ratios. Also, the effects are much more severe when only analyte and concomitant are present in contrast to solutions containing other salts, i.e. a sample matrix. Though we cannot yet offer a complete explanation for the suppressions, definite stoichiometry is indicated in reactions involving the solid phase after desolvation and prior to vaporization.     

NCO quantitative measurement in premixed low pressure flames by combining LIF and CRDS techniques

NCO is a short-lived species involved in NO(x) formation. It has never been quantitatively measured in flame conditions. In the present study, laser-induced fluorescence (LIF) and cavity ring-down spectroscopy (CRDS) were combined to measure NCO radical concentrations in premixed low-pressure flames (p = 5.3 kPa). NCO LIF excitation spectrum and absorption spectrum (using CRDS) measured in a stoichiometric CH(4)/O(2)/N(2)O/N(2) flame were found in good agreement with a simulated spectrum using PGOPHER program that was used to calculate the high-temperature absorption cross section of NCO in the A(2)Σ(+)-X(2)Π transition around 440.479 nm. The relative NCO-LIF profiles were measured in stoichiometric CH(4)/O(2)/N(2)O/N(2) flames where the ratio N(2)O/O(2) was progressively decreased from 0.50 to 0.01 and in rich CH(4)/O(2)/N(2) premixed flames. Then, the LIF profiles were converted into NCO mole fraction profiles from the absorption measurements using CRDS in a N(2)O-doped flame.     

Experimental and modelling study of sulfur and nitrogen doped premixed methane flames at low pressure

Laser-induced fluorescence (LIF) has been used to observe NS and NO in methane/oxygen/argon laminar flames at low pressure doped with ammonia and sulfur dioxide. NS profiles as a function of height above the burner have been measured for rich flames. The effect of adding various amounts of sulfur dioxide on the observed NO in the burnt gas region has been investigated for a variety of stoichiometries. The experimental measurements have been compared with PREMIX simulations using a detailed elementary reaction mechanism for nitrogen- and sulfur-containing species in a methane flame. Sensitivity analysis has been employed to highlight the important reactions for NS, NO and SO2. The results demonstrate significant uncertainties in currently best available rate data for important reactions involving sulfur-containing species.     

An evaluation of the spectral noise distribution in analytical flames

The spectral distribution of noises (total, shot and flicker) in a variety of flames has been measured using a computer-controlled spectrometer system. Emission spectra and fluorescence spectra (excited by an Eimac xenon arc lamp) are presented for air/acetylene, nitrous oxide/acetylene, nitrous oxide/propane, air/hydrogen, and an iso-octane liquid fuel flame. Conclusions concerning the predominant type of noise and its cause in each flame are discussed as well as the implications for the analytical flame spectroscopist.     

Wavelength modulation diode laser atomic absorption spectrometry in analytical flames

The potential of wavelength modulation laser atomic absorption spectrometry in analytical flames is demonstrated by the measurement of titanium, cesium and chromium applying fundamental and frequency doubled radiation of commercially available semiconductor diode lasers. In dependence on the radiation power, absorbances of the order of 10⁻⁴–10⁻⁶ are measured, which reveal very low detection limits even when weak absorption lines are used.     

Unraveling chemical structure of laminar premixed tetralin flames at low pressure with photoionization mass spectrometry and kinetic modeling

This work reports an investigation on laminar premixed flames of tetralin at 30 Torr and equivalence ratios of 0.7 and 1.7. Measurements of the chemical structure including identification and mole fraction measurements of free radicals, isomers, and polycyclic aromatic hydrocarbons (PAHs) were performed using synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV‐PIMS). A kinetic model with 296 species and 1 577 reactions was developed and validated against the flame chemical structure data measured in this work. Modeling analysis reveals the key reaction pathways in tetralin decomposition and PAHs formation. The H‐atom abstraction reactions by H, O, and OH are found to control the consumption of tetralin in the lean flame, while those by H play the dominant role in the rich flame. Indene and naphthalene have very high concentration levels in the rich tetralin flame due to the existence of direct formation pathways from the decomposition of tetralin. The two bicyclic PAHs and their radicals play significant roles in the PAHs growth process of tetralin combustion, which results in the high sooting tendency of tetralin compared to those of alkylbenzenes with smaller or same carbon atom numbers.     

Teaching analytical properties

A new way of expounding analytical properties based on their mutual dependence (complementary and contradictory relationships) and their unequivocal connection with analytical quality facets is presented. To this end, the paper provides answers to the obvious questions that arise in dealing with the subject: why?, how?, when? and where to teach analytical properties in the Analytical Chemistry curriculum?     

Some derivatives of rhodanine as analytical reagents

Twenty-two derivatives of rhodanine were investigated as potential spectrophotometric and spot test reagents. Sensitive reactions for silver, gold, copper(I), mercury(II), palladium and some other metals are described. None of the reagents is suitable for spectrophotometry ; all but one produce non-extractable, colloidal, metal-ion complexes. The introduction of a sulphonic acid group into the molecule, however, makes the complexes water-soluble.     

Emission spectra of nitrous oxide supported acetylene flames at atmospheric pressure

The emission spectra of a premixed flame of acetylene supported by nitrous oxide have been recorded under different fuel-gas mixture conditions. The emission spectra in these flames of a series of metals, for which it is difficult to obtain a significant population of ground state atoms for atomic absorption spectroscopy in more conventional flames, have also been studied. The red secondary zone which is present in the fuel-rich flames shows emission attributable to long-lived CN and NH species which form a strongly reducing atmosphere to inhibit refractory oxide formation from elements such as molybdenum, titanium and aluminium introduced into the flame. An attempt has also been made to explain some of the reactions which may occur between the flame species above the primary reaction zone.     

Some fundamental considerations on analytical high-frequency plasmas

Several possible models for plasmas, and their fundamental background, are discussed. The recent literature on investigations of fundamental plasma models and plasma parameters is reviewed.     

Some new heterocyclic compounds as analytical reagents

A survey of the metal-complexing reactions, as determined by reactions on chromatography paper, of 44 compounds with a substituted or modified 4-(2-pyridylazo)-resorcinol (PAR) or 1-(2-pyridylazo)-2-naphthol (PAN) structure is reported.     

Temperature profiles in nitrous oxide supported acetylene flames at atmospheric pressure

Temperature profiles have been established at three mixture strengths of the nitrous oxide-acetylene flame used in atomicabsorption spectroscopy. Measurement of the electronic excitation temperature of the red-feather zone by the sodium line-reversal and iron two-line methods yields average maximum temperatures of 3070 and 3025 +/- 50 degrees K respectively. This is significantly lower than the only previously reported value, 3228 degrees K. Other temperature measurements obtained by studying intensity distribution of NH rotational fine structure and CN vibrational structure yielded less precise results, but suggest a state of thermal equilibrium in the flame. The temperature gradient within the flame shows a steady decrease with height above the primary zone. A study of CN spectra and the zones of persistence of free atoms and of metal oxide species suggests a mechanism of free atom production within the cyanogen zone whereby the removal of oxidizing radicals by CN promotes dissociation of metal oxide species previously formed in the primary zone of the flame.     

Some electrophysical properties of polyphthalocyanines under the action of high pressure and shear deformation

The effect of high pressure or the combined action of high pressure and shear deformation on the conductivity G and capacitance C of metal-free polyphthalocyanines (PPhCs), differing in macromolecular size, order, and degree of crosslinking, has been studied. It has been found that both G and C increase with compression. A similar phenomenon is observed under the combined action of high pressure and shear deformation on PPhC, but in this case the critical pressure needed for change in G is lower than that observed in uniaxial compression experiments. Spectroscopic investigations show that the effects of pressure and deformation on the electrophysical properties of samples under load is not connected with changes in the chemical structure of PPhC, but appear to be due to the change in the average distance between the regions of continuous conjugation. The sizes of such regions may be increased by preliminary thermal treatment.