Electronic transition moment of the AΠr-XΣ system of TiN

The A²Π_r-X²Σ⁺ transition of TiN was observed by the dispersed laser induced fluorescence (DLIF) spectroscopy. The relative intensities of the DLIF spectra were analyzed to determine the dependence of the electronic transition moment, R_e(r), on the internuclear distance, r, as R_e(r)∝{1−0.281(26)r} (1.380 Å≤r≤1.823 Å). This r-dependence was analyzed simultaneously with the reported values of the spin-orbit constants for A²Π_r and the hyperfine-coupling constants for X²Σ⁺ to evaluate the ionic character of the TiN bond, the 4s atomic character in the 9σ orbital of X²Σ⁺, and the 4p atomic character in the 4π orbital of A²Π_r. These characters were confirmed to be in accordance with the reported theoretical prediction. A strong r-dependence was indicated for the 3d-4p mixing in the A²Π_r state due to the configuration mixing of the Ti(3d⁴) and Ti(3d³4p) states at a large internuclear distance.     

Deactivation of CO(AΠ) in individual vibrational levels

Resonance absorption of CO(A¹Π → X¹Σ⁺) fourth positive bands was used to excite CO molecules selectively into the ν′ = 0 and ν′ = 1 vibrational levels of the A¹Π state. Studies of the fluorescence spectra at different added gas pressures yielded effective cross sections for the vibrational relaxation of A¹Π, ν′ = 1 and for the quenching of A¹π, ν′ = 0 molecules. Very large cross sections up to gas kinetic were measured for the rare gases He, Ne, Ar, and Kr as well as for the molecular species H₂, D₂ and N₂     

Advantages and effects of nitrogen doping into the central channel of plasma in axially viewed-inductively coupled plasma optical emission spectrometry

The effects and benefits of N₂ addition to the central channel of the ICP through the nebulizer gas used in ICP OES with axial view configuration were investigated in the present study. The N₂ flow rate, nebulizer gas flow rate, RF power and sample uptake rate were evaluated and compared for two sample introduction systems (pneumatic nebulization/aerosol desolvation and conventional pneumatic nebulization). It was observed that N₂ did not affect solution nebulization and aerosol transport but affects the ICP characteristics. The higher thermal conductivity of N₂ (in comparison with Ar) changes energy distribution in the ICP, observed by monitoring the signals of Ar emission lines and sodium emission. The ratio Mg(II)-280.270 nm/Mg(I)-285.213 nm was utilized as a diagnostic tool for plasma robustness. The addition of N₂ (20 mL min⁻¹) increased plasma robustness significantly and mitigated effects caused by Na, K and Ca. For 40 spectral lines evaluated, it was observed that the emission signals of ionic spectral lines were in general more affected by N₂ than those of atomic spectral lines. Detection limits, precision, sensitivity and linearity of calibration curves obtained using N₂-Ar-ICP were almost similar to those obtained using Ar-ICP. The analysis of 5 different reference materials revealed that accuracy was not degraded by adding N₂ to the Ar-ICP.     

Laser Ablation Molecular Isotopic Spectrometry: Parameter influence on boron isotope measurements

Laser Ablation Molecular Isotopic Spectrometry (LAMIS) was recently reported for optical isotopic analysis of condensed samples in ambient air and at ambient pressure. LAMIS utilizes molecular emissions which exhibit larger isotopic spectral shits than in atomic transitions. For boron monoxide ¹⁰BO and ¹¹BO, the isotopic shifts extend from 114 cm⁻¹ (0.74 nm) to 145–238 cm⁻¹ (5–8 nm) at the B²Σ⁺ (v = 0) → X²Σ⁺ (v = 2) and A²Π_i (v = 0) → X²Σ⁺ (v = 3) transitions, respectively. These molecular isotopic shifts are over two orders of magnitude larger than the maximum isotopic shift of approximately 0.6 cm⁻¹ in atomic boron. This paper describes how boron isotope abundance can be quantitatively determined using LAMIS and how atomic, ionic, and molecular optical emission develops in a plasma emanating from laser ablation of solid samples with various boron isotopic composition. We demonstrate that requirements for spectral resolution of the measurement system can be significantly relaxed when the isotopic abundance ratio is determined using chemometric analysis of spectra. Sensitivity can be improved by using a second slightly delayed laser pulse arriving into an expanding plume created by the first ablation pulse.     

Spatially resolved temperature measurements in a furnace atomization plasma excitation spectrometry source

Spatially resolved atomic emission intensities from helium, and molecular emission intensities from OH and N⁺₂ have been measured in a furnace atomization plasma excitation spectrometry (FAPES) source. He I emission at 388.86 nm was used to monitor the spatial structure of the plasma in the source while increasing the radio frequency (r.f.) power applied to its center electrode. At higher r.f. power the He I emission intensity increased significantly while its spatial structure remained relatively unchanged. The He I emission was found to be most intense adjacent to the center electrode. Some less intense emission was observed adjacent to the graphite cuvette wall and some very weak emission was seen throughout the volume of the source. These observations suggest that the FAPES source operates as an r.f. glow discharge.Emission intensities from the OH (0-0) rotational A ²Σ⁺ → X ²Π_i and N⁺₂ (0-0) rotational B ²Σ⁺_o → ²Σ⁼_g bands were used to monitor the effects of increasing the r.f. power applied to the center electrode of the source. From these measurements, rotational temperatures for these molecules were calculated. The intensity measurements showed that there is a significant thermal gradient in the source with OH rotational temperatures ranging between 680 and 1050 K and N⁺₂ rotational temperatures ranging between 580 and 1920 K with 60 W r.f. power applied to the center electrode. At higher r.f. powers there is an increase in rotational temperatures and an increase in the dissociation of molecular species in the FAPES source.Lead excitation temperatures were calculated using the line ratio method by measuring the emission of the Pb I 280.119 and 283.306 nm lines at different r.f. powers. The temperature was found to increase monotonically with r.f. power over the range of 35 to 75 W.     

Determination of thiomersal by flow injection coupled with microwave-assisted photochemical online oxidative decomposition of organic mercury and cold vapor atomic fluorescence spectroscopy

We developed a flow injection (FI) method for the determination of thiomersal (sodium ethylmercurithiosalicylate, C₉H₉HgNaO₂S) based on the UV/microwave (MW) photochemical, online oxidation of organic mercury, followed by cold vapor generation atomic fluorescence spectrometry (CVG-AFS) detection. Thiomersal was quantitatively converted in the MW/UV process to Hg(II), with a yield of 97 ± 3%. This reaction was followed by the reduction of Hg(II) to Hg(0) performed in a knotted reaction coil with NaBH₄ solution, and AFS detection in an Ar/H₂ miniaturized flame. The method was linear in the 0.01–2 μg mL⁻¹ range, with a LOD of 0.003 μg mL⁻¹. This method has been applied to the determination of thiomersal in ophthalmic solutions, with recoveries ranging between 97% and 101%. We found a mercury concentration in commercial ophthalmic solutions ranging between 7.5 and 59.0 μg mL⁻¹.     

Optical study of diffuse bi-directional nanosecond pulsed dielectric barrier discharge in nitrogen

In this study, a bi-directional high voltage pulse with 20 ns rising time is employed to generate diffuse glow-like dielectric barrier discharge plasma with very low gas temperature in N2 using needle-plate electrode configuration at atmospheric pressure. Both the diffuse nanosecond pulsed dielectric barrier discharge images and the optical emission spectra of the discharge are recorded successfully under severe electromagnetic interference. The effects of pulse peak voltage, pulse repetition rate, and the concentrations of Ar and O2 on the emission intensities of NO (A2Σ→X2Π), OH (A2Σ→X2Π, 0-0), N2 (C3Πu→B3Πg, 0-0, 337.1 nm), and N2+ (B2Σu+→X2Σg+, 0-0, 391.4 nm) are investigated. The effects of the concentrations of Ar and O2 on the discharge diffuse performance are also studied. It is found that the emission intensities of NO (A2Σ→X2Π), OH (A2Σ→X2Π, 0-0), N2 (C3Πu→B3Πg, 0-0, 337.1 nm), and N2+ (B2Σu+→X2Σg+, 0-0, 391.4 nm) rise with increasing pulse peak voltage, pulse repetition rate, and the concentration of Ar, but decrease with increasing the concentration of O2. The main physicochemical processes involved are also discussed.     

Photoexcitation of CH3NCO,CH3NCS and CH3SCN in the vacuum ultraviolet: Rydberg states and photofragment emission

Photoabsorption cross sections and fluorescence excitation spectra of CH₃NCO, CH₃NCS and CH₃SCN vapor were measured in the vacuum ultraviolet using synchrotron radiation. Many sharp structures observed from CH₃NCO and CH₃SCN in the 120–180 nm region are classified into three Rydberg series and their vibrational progressions, whereas for CH₃NCS six broad bands exhibit no fine structure. The emission which starts to appear at 172.8 ± 1.0 nm excitation of CH₃NCO is attributed to the NCO(A²Σ⁺-X²Π) band. The emissions from CH₃NCS and CH₃SCN are assigned to the A²Π-X²Π and B²Σ⁺-X²Π bands of NCS; the CN(B²Σ⁺-X²Σ⁺) band is also observed at 125 nm excitation of CH₃SCN. The photodissociation processes are discussed in accord with the emission observed.     

Theoretical study on the reaction mechanism of CH4 with CaO

The reaction pathways and energetics for the reaction of methane with CaO are discussed on the singlet spin state potential energy surface at the B3LYP/6-311+G(2df,2p) and QCISD/6-311++G(3df,3pd)//B3LYP/6-311+G(2df,2p) levels of theory. The reaction of methane with CaO is proposed to proceed in the following reaction pathways: CaO + CH₄ → CaOCH₄ → [TS] → CaOH + CH₃, CaO + CH₄ → OCaCH₄ → [TS] → HOCaCH₃ → CaOH + CH₃ or [TS] → CaCH₃OH → Ca + CH₃OH, and OCaCH₄ → [TS] → HCaOCH₃ → CaOCH₃ + H or [TS] → CaCH₃OH → Ca + CH₃OH. The gas-phase methane–methanol conversion by CaO is suggested to proceed via two kinds of important reaction intermediates, HOCaCH₃ and HCaOCH₃, and the reaction pathway via the hydroxy intermediate (HOCaCH₃) is energetically more favorable than the other one via the methoxy intermediate (HCaOCH₃). The hydroxy intermediate HOCaCH₃ is predicted to be the energetically most preferred configuration in the reaction of CaO + CH₄. Meanwhile, these three product channels (CaOH + CH₃, CaOCH₃ + H and Ca + CH₃OH) are expected to compete with each other, and the formation of methyl radical is the most preferable pathway energetically. On the other hand, the intermediates HCaOCH₃ and HOCaCH₃ are predicted to be the energetically preferred configuration in the reaction of Ca + CH₃OH, which is precisely the reverse reaction of methane hydroxylation.     

Collisional quenching of NO(A,v' =0) by various gases

The rate coefficients for the quenching of NO(A ²Σ, v' =0) by NO, N₂O, H₂O, O₂, SF₆ and CO₂ were measured to be (in units of 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹): 2.67±0.41, 3.79±0.49, 7.8±1.0, 1.46±0.25, 3.82±0.49, and 4.30±0.26, respectively. Upper limits for the quenching rate constants by N₃, Ar, Ne, H₂, and CF₄ were also measured. All experiments were carried out by monitoring the temporal profiles of A ²Σ, v' =O→X²Π, v″=3 fluorescence after 226 nm pulsed laser excitation of NO(X²Π) to NO(A²Σ,v'=0).     

Laser-induced fluorescence in N2 and N+2 by multiple-photon excitation at 266 nm

The fluorescence transitions corresponding to the second positive system of N₂ (C³Π_u → B³Π_g) for Δv = 0, 1 and the first negative system of N⁺₂(B²Σ⁺_u → X²Σ⁺_g) for Δv = 0, 1, 2 have been observed following laser-induced mul excitation of N₂.     

Chemiluminescent emissions from the gas phase reactions of ozone with acetylene and allene

Chemiluminescence spectra (300–800 nm) from the reactions of ozone with acetylene and allene have been obtained. These spectra show the production of electronically excited CHO, OH(²Π_i, υ ? 9) and possibly C₂(B³Π_g, υ′ = 0 → X³Π_u, υ″ = 6) from the O₃ + C₂H₂ reaction. CH(²Δ), OH(²Σ⁺) and OH(²Π_j, υ ? 9) emissions were identified from the O₃ + C₃H₄ reaction in addition to the CH₂O(¹A″) emission previously reported.     

Ion pair-based dispersive liquid-liquid microextraction for gold determination at ppb level in solid samples after ultrasound-assisted extraction and in waters by electrothermal-atomic absorption spectrometry

A new methodology was developed for the determination of ultratrace levels of gold in water samples, soils and river sediments. Dispersive liquid-liquid microextraction was used to preconcentrate the ion pair formed between AuCl₄⁻ and [CH₃(CH₂)₃]₄N⁺ in a microliter-range volume of chlorobenzene using acetone as disperser solvent. When solid samples were analyzed, the method consisted of a combination of ultrasound-assisted extraction and dispersive liquid-liquid microextraction with final detection by electrothermal-atomic absorption spectrometry. Since an HCl medium was required for the formation of the AuCl₄⁻ complex, HCl together with HNO₃ was used as extractants for ultrasound-assisted extraction. After optimization, the enrichment factor obtained was 220 for water samples. Moreover, the extraction efficiency was around 96%. The repeatability, expressed as relative standard deviation ranged from 3.6% to 9.7%. The instrumental detection limit was 8.4 ng L⁻¹, whereas the procedural detection limits were 42 ng L⁻¹ for water samples and 1.5 ng g⁻¹ for environmental solid samples.     

Theoretical spectroscopy and metastability of BeS and its cation

Multiconfiguration self-consistent field and multiconfiguration reference interaction including the Davidson’s correction techniques were employed to calculate the potential energy curves (PECs) of the BeS/BeS⁺ electronic states correlating to the 4/5 lowest dissociation limits. After nuclear motion treatment, we deduced reliable spectroscopic data for the neutral and cationic bound states. For BeS, the transition moments and spin-orbit couplings were also evaluated and used later with the PECs to deduce the rovibronic transition probabilities and the radiative lifetimes in the low-lying states, and to investigate the unimolecular decomposition processes of BeS (X¹Σ⁺, A¹Π, ³Σ⁺ and B¹Σ⁺) leading to Be(¹S_g) + S(³P_g). The prominent mechanism is a spin-orbit induced predissociation via the repulsive BeS(1³Σ⁻) state. Finally, we give the single ionization spectrum of BeS (X¹Σ⁺) populating the BeS⁺ (X²Π, 1²Σ⁻, 1²Σ⁺, 1²Δ, 2²Σ⁺, 2²Π and 3²Π) electronic states. The adiabatic ionisation energy of BeS is estimated to be ∼9.15 eV.     

Vacuum UV emission by electronically excited N2: The collision-induced N2(a 1Πg′ υ = 0) ↔ N2(a′1Σu−, υ = 0) transition

A weak discharge through a flowing Ar/N₂ mixture provides a source of metastable N₂(a′¹Σ_u^?) molecules in the absence of N atoms. Vacuum UV emission is observed from this state and from N₂(a ¹Π_g), which is populated by collisional excitation of a′¹Σ_u^? state molecules.     

Vacuum UV emission by electronically-excited N2: The radicative lifetime of the N2(a′1Σ−u state

A measurement of the electronic transition moment variation for the N₂(a'¹Σ^?_uX¹Σ^+g) band system has allowed a reassessment of the radiative lifetime of N₂(a′). Relaxation to N₂(a′,υ=0) is established as the major channel for quenching of N₂(a¹Π_g, υ = 0) molecules by Ar.     

Optical emission spectrometric determination of arsenic and antimony by continuous flow chemical hydride generation and a miniaturized microwave microstrip argon plasma operated inside a capillary channel in a sapphire wafer

Continuous flow chemical hydride generation coupled directly to a 40 W, atmospheric pressure, 2.45 GHz microwave microstrip Ar plasma operated inside a capillary channel in a sapphire wafer has been optimized for the emission spectrometric determination of As and Sb. The effect of the NaBH₄ concentration, the concentration of HCl, HNO₃ and H₂SO₄ used for sample acidification, the Ar flow rate, the reagent flow rates, the liquid volume in the separator as well as the presence of interfering metals such as Fe, Cu, Ni, Co, Zn, Cd, Mn, Pb and Cr, was investigated in detail. A considerable influence of Fe(III) (enhancement of up to 50 %) for As(V) and of Fe(III), Cu(II) and Cr(III) (suppression of up to 75%) as well as of Cd(II) and Mn(II) (suppression by up to 25%) for Sb(III) was found to occur, which did not change by more than a factor of 2 in the concentration range of 2–20 μg ml^− 1. The microstrip plasma tolerated the introduction of 4.2 ml min^− 1 of H₂ in the Ar working gas, which corresponded to an H₂/Ar ratio of 28%. Under these conditions, the excitation temperature as measured with Ar atom lines and the electron number density as determined from the Stark broadening of the H_β line was of the order of 5500 K and 1.50 · 10¹⁴ cm^− 3, respectively. Detection limits (3σ) of 18 ng ml^− 1 for As and 31 ng ml^− 1 for Sb were found and the calibration curves were linear over 2 orders of magnitude. With the procedure developed As and Sb could be determined at the 45 and 6.4 μg ml^− 1 level in a galvanic bath solution containing 2.5% of NiSO₄. Additionally, As was determined in a coal fly ash reference material (NIST SRM 1633a) with a certified concentration of As of 145 ± 15 μg g^− 1 and a value of 144 ± 4 μg g^− 1 was found.     

Investigation on sensitized chemiluminescence systems and their mechanism for five fluoroquinolones

The novel chemiluminescence (CL) reaction systems were established for lomefloxacin (LMFX), ofloxacin(OFLX), norfloxacin (NFLX), gatifloxacin (GAFX) and enoxacin (ENX). The sensitized CL emission mechanism was investigated for the five systems by comparing the fluorescence emission with CL spectra. For LMFX-Ce(IV)-S₂O₃²⁻-H₂SO₄ and OFLX-Ce(IV)-S₂O₄²⁻-H₂SO₄ systems, the CL intensity is enhanced through intermolecular energy transfer from the excited SO₂^* to LMFX and OFLX. For NFLX-Ce(IV)-S₂O₄²⁻-HNO₃ system, the sensitized CL is based on intermolecular energy transfer from the excited SO₂^* to NFLX oxide. For Eu³⁺-GAFX-Ce(IV)-S₂O₄²⁻-HCl and Dy³⁺-ENX-Ce(IV)-S₂O₃²⁻-H₂SO₄ systems, the CL spectra are from the narrow characteristic emission at 590, 619 and 649 nm of Eu^3+* (⁵D₀ → ⁷F₁, ⁵D₀ → ⁷F₂, ⁵D₀ → ⁷F₃) and at 482 and 578 nm of Dy³⁺ (⁴F₉ → ⁶H_15/2, ⁴F₉ → ⁶H_13/2) through intermolecular energy transfer from the excited SO₂^* to GAFX and ENX, followed by intramolecular energy transfer from GAFX^* to Eu³⁺ and ENX^* to Dy³⁺. The conditions of CL emission were investigated and optimized. The proposed five enhanced CL systems have good linearity, higher sensitivity, precision and potential capability for residue analysis of studied analytes in foods and biological samples.     

Near-infrared fluorimetric determination of nucleic acids by shifting the ion-association equilibrium between tetracarboxy aluminum phthalocyanine and tetra-N-hexadecylpyridiniumyl porphyrin

A new method was developed for determination of micro amounts of nucleic acids based on near-infrared (near-IR) fluorescence recovery, employing a two-reagent system which is composed of an anionic tetracarboxy aluminum phthalocyanine (AlC₄Pc) and a cationic tetra-N-hexadecylpyridiniumyl porphyrin (TC₁₆PyP). The fluorescence of the AlC₄Pc, with the maximum emission wavelength at 701 nm, could be quenched by TC₁₆PyP at its proper concentration, but recovered by adding nucleic acids. Under optimal conditions, the recovered fluorescence is proportional to the concentration of nucleic acids. The calibration graphs are linear over the range of 1-200 ng mL⁻¹ for fish sperm DNA (FS DNA) and 2-400 ng mL⁻¹ for calf thymus DNA (CT DNA). The corresponding detection limits are 0.59 ng mL⁻¹ for FS DNA and 0.82 ng mL⁻¹ for CT DNA, respectively. Four synthetic and three real nucleic acid samples were determined with satisfactory results.     

Automatic on line preconcentration and determination of lead in water by ICP-AES using a TS-microcolumn

A simple, sensitive, low-cost and rapid, flow injection system for the on-line preconcentration of lead by sorption on a microcolumn packed with silica gel funtionalized with methylthiosalicylate (TS-gel) was developped. The metal is directly retained on the sorbent column and subsequently then eluted from it by EDTA. Five variables (sample flow rate, eluent flow rate, eluent concentration, pH and buffer concentration) were considered as factors in the optimization process. Interactions between analytical factors and their optimal levels were investigated using two level factorial and Box-Behnken designs. The optimum conditions established were applied to the determination of lead by flow injection inductively coupled plasma atomic emission spectrometry (FI-ICP-AES). The proposed method has a linear calibration range from 10 to at least 500 ng ml⁻¹ of lead. At a sample frequency of 24 h⁻¹ and a 120 s preconcentration time, the enrichment factor was 41, the detection limit was 15.3 ng ml⁻¹ (S/N=3) and the precision, expressed as relative standard deviation, was 0.9% (at 100 ng ml⁻¹). Validation of the developed method was carried out against electrothermal atomic absorption spectrometry analysis without statistically significant differences between the proposed method and the atomic absorption method.