Radiative lifetimes and Lande factors of Rydberg 6pnp and 6pnf states of PbI by multichannel-quantum-defect theory

Multichannel-quantum-defect theory analyses of J = 0, 1, and 2 even-parity Rydberg series 6pnp and 6pnf of neutral lead have been performed for the experimental energy levels, The channel admixture coefficients were deduced and used to evaluate theoretical lifetimes and Lande (g(J)) factors. Lifetime and g(J) values for higher-lying excited states have also been predicted

Spectrally Arbitrary Tree Sign Pattern Matrices

A sign pattern (matrix) is a matrix whose entries are from the set {+,–, 0}. A sign pattern matrix A is a spectrally arbitrary pattern if for every monic real polynomial p(x) of degree n there exists a real matrix B whose entries agree in sign with A such that the characteristic polynomial of B is p(x). All 3 × 3 SAP\u27s, as well as tree sign patterns with star graphs that are SAP\u27s, have already been characterized. We investigate tridiagonal sign patterns of order 4. All irreducible tridiagonal SAP\u27s are identified. Necessary and sufficient conditions for an irreducible tridiagonal pattern to be an SAP are found. Some new techniques, such as innovative applications of Gröbner bases for demonstrating that a sign pattern is not potentially nilpotent, are introduced. Some properties of sign patterns that allow every possible inertia are established. Keywords: Sign pattern matrix, Spectrally arbitrary pattern (SAP), Inertially arbitrary pattern (IAP), Tree sign pattern (tsp), Potentially nilpotent pattern, Gröbner basis, Potentially stable pattern, Sign nonsingular, Sign singula

Quantitative SO2 Detection in Combustion Environments Using Broad Band Ultraviolet Absorption and Laser-Induced Fluorescence

Spectrally resolved ultraviolet (UV) absorption cross sections of SO2 in combustion environments at temperatures from 1120 to 1950 K were measured for the first time in well-controlled conditions through applying broad band UV absorption spectroscopy in specially designed one-dimensional laminar flat flames. The temperature was observed to have a significant effect on the absorption cross-section profiles at wavelength shorter than 260 nm, while at the longer wavelength side, the absorption cross-section profiles have much less dependence on temperature. The absorption cross section at 277.8 nm with a value of 0.68 × 10-18 cm2/molecule was suggested for the evaluation of the SO2 concentration because of the weak dependence on temperature. To make spatially resolved measurements, laser-induced fluorescence (LIF) of SO2 excited by a 266 nm laser was investigated. Spectrally resolved LIF signal was analyzed at different temperatures. The LIF signal showed strong dependence on temperature, which can potentially be used for temperature measurements. At elevated temperatures, spatially resolved LIF SO2 detection up to a few ppm sensitivity was achieved. Combining UV broad band absorption spectroscopy and LIF, highly sensitive and spatially resolved quantitative measurements of SO2 in the combustion environment can be achieved

Quantitative imaging of KOH vapor in combustion environments using 266 nm laser-induced photofragmentation fluorescence

In biomass thermal conversion processes, the release of potassium in high temperature environments crucially influences the operating efficiency and safety. The dominant potassium species can be potassium hydroxide (KOH) and/or potassium chloride (KCl). We report a species-specified quantitative measurement of potassium hydroxide (KOH) in combustion environments using laser-induced photofragmentation fluorescence (LIPF). Ultraviolet (UV) light sources with different wavelengths (193, 213 and 266 nm) were investigated to select a proper source ensuring that the excited potassium atoms in the 42P state could be only generated from the KOH molecules, not another major potassium compound, potassium chloride (KCl), and emit fluorescence at 766/769 nm after the photodissociation. After direct comparison, the fourth-harmonic of Nd:YAG laser at 266 nm was found to be the most proper light source. The fluorescence signal was strongly influenced by temperature as KOH molecules at thermally populated excited vibrational levels were needed to produce excited potassium atoms after the 266 nm photolysis. After the calibration using broadband UV absorption spectroscopy, the detection limit of the LIPF planar imaging system was determined to be about 3 ppm at 1750 K under a harsh condition, where about 80% of the fluorescence was re-absorbed by the potassium atoms present in the background gas. The technique was applied to quantitatively measure KOH concentration in the hot flue gasses provided by potassium carbonate seeded flames with varying equivalence ratios, and it was also used to visualize the distribution of KOH vapor above a piece of burning wood char

Simultaneous quantitative detection of hcn and c2h2 in combustion environment using tdlas

Emission of nitrogen oxides (NOx ) and soot particles during the combustion of biomass fuels and municipal solid waste is a major environmental issue. Hydrogen cyanide (HCN) and acetylene (C2H2 ) are important precursors of NOx and soot particles, respectively. In the current work, infrared tunable diode laser absorption spectroscopy (IR-TDLAS), as a non-intrusive in situ technique, was applied to quantitatively measure HCN and C2H2 in a combustion environment. The P(11e) line of the first overtone vibrational band v1 of HCN at 6484.78 cm−1 and the P(27e) line of the v1 + v3 combination band of C2H2 at 6484.03 cm−1 were selected. However, the infrared absorption of the ubiquitous water vapor in the combustion environment brings great uncertainty to the measurement. To obtain accurate temperature-dependent water spectra between 6483.8 and 6485.8 cm−1, a homogenous hot gas environment with controllable temperatures varying from 1100 to 1950 K provided by a laminar flame was employed to perform systematic IR-TDLAS measurements. By fitting the obtained water spectra, water interference to the HCN and C2H2 measurement was sufficiently mitigated and the concentrations of HCN and C2H2 were obtained. The technique was applied to simultaneously measure the temporally resolved release of HCN and C2H2 over burning nylon 66 strips in a hot oxidizing environment of 1790 K

Ultraviolet Absorption Cross-Sections of Ammonia at Elevated Temperatures for Nonintrusive Quantitative Detection in Combustion Environments

Ammonia (NH3) is regarded as an important nitrogen oxides (NOx) precursor and also as an effective reductant for NOx removal in energy utilization through combustion, and it has recently become an attractive non-carbon alternative fuel. To have a better understanding of thermochemical properties of NH3, accurate in situ detection of NH3 in high temperature environments is desirable. Ultraviolet (UV) absorption spectroscopy is a feasible technique. To achieve quantitative measurements, spectrally resolved UV absorption cross-sections of NH3 in hot gas environments at different temperatures from 295 K to 590 K were experimentally measured for the first time. Based on the experimental results, vibrational constants of NH3 were determined and used for the calculation of the absorption cross-section of NH3 at high temperatures above 590 K using the PGOPHER software. The investigated UV spectra covered the range of wavelengths from 190 nm to 230 nm, where spectral structures of the (Formula presented.) transition of NH3 in the umbrella bending mode, v2, were recognized. The absorption cross-section was found to decrease at higher temperatures. For example, the absorption cross-section peak of the (6, 0) vibrational band of NH3 decreases from ∼2 × 10−17 to ∼0.5 × 10−17 cm2/molecule with the increase of temperature from 295 K to 1570 K. Using the obtained absorption cross-section, in situ nonintrusive quantification of NH3 in different hot gas environments was achieved with a detection limit varying from below 10 parts per million (ppm) to around 200 ppm as temperature increased from 295 K to 1570 K. The quantitative measurement was applied to an experimental investigation of NH3 combustion process. The concentrations of NH3 and nitric oxide (NO) in the post flame zone of NH3–methane (CH4)–air premixed flames at different equivalence ratios were measured