Non-thermal Excitation Research Articles

Nonthermal excitation of helium in type Ib supernovae

The presence of strong He I absorption troughs in the optical spectra of type Ib SNs is attributed to non-thermal excitation. As for analogous in the premaximum spectra of SN 1987A, the early importance of nonthermal excitation in the Ib's is fundamentally due to a large-scale instability that mixes 56 Ni out into their envelopes shortly after the explosion. Because of this mixing, the helium-rich envelopes of these SNs are, even at maximum light, not strongly shielded form the γ-rays emitted by 56 Co nuclei. A non-LTE treatment of this non-thermal excitation of helium is given using a recent model of a type Ib SN that invokes mixing of 56 Ni in order to reproduce light curves.

Graphite furnace analysis—getting easier and achieving more?

The impact of microwave digestion, hot injection of solutions and chemical modification on the analysis of biological samples by electrothermal atomic absorption spectrometry (AAS) has been assessed. The stabilizing effects of palladium and ruthenium modifiers were compared. Although ruthenium has a higher atom appearance temperature, palladium was the more useful modifier when samples other than water were analysed. When 2 μg of palladium (as PdCl 2) was preconditioned in hydrogen at 500°C, volatile elements were retained at char temperatures up to 1000–1100°C. This allowed similar atomizer programmes to be used for Cd, Cu, Fe, Mn and Pb and accurate determination of these analytes in solutions of reference materials was achieved aqueous standards. Rapid drying of the solutions by hot injection at 120°C reduced the programme time to just over 1 min. A combination of microwave digestion, hot injection of 40% (w/v) HNO 3 solutions and Pd modification produced a rapid and sensitive method for determination of Cd and Pb at sub-μg g −1 levels in vegetable and protein foodstuffs. Palladium modification also proved useful in simultaneous multi-element determination by continuum source AAS. The picogram detection limits obtained for Cr, Mn and Pb were similar to line source AAS values recorded with the same compromise programme. Accurate determination of Cd, Cr, Cu, Mn, Mo and Pb in NIST SRM 1566 Oyster Tissue indicated the potential of continuum source AAS for multi-element determinations. The advantages of palladium modifications were also illustrated for furnace atomic non-thermal excitation spectrometry ( FANES) with a hollow-cathode discharge. The maximum char temperatures of Ag, Ga, Hg, Pb, Sb and Se were increased by 300–600°C in the presence of 1 μg of Pd, although the detection limits were a factor of two poorer.

Emission characteristics of chromium in hollow anode-furnace atomization non-thermal excitation spectrometry

Emission parameters for the determination of Cr using hollow anode-furnace atomization non-thermal excitation spectrometry (HA-FANES) were investigated. The spectral background between 280 and 400 nm included strong emission bands from CN, NH and CH. The best signal-to-noise ratio for Cr was observed for the atomic line at 359.3 nm. Argon atomic emission (420.1 nm) showed no decrease in intensity in the presence of thermionic electrons while Ar ionic emission (434.8 nm) showed a dramatic decrease in intensity. The integrated Cr emission signal exhibited a broad maximum between atomization temperatures of 1800 and 2100°C. Peak areas increased with pressure with the best signal-to-noise ratio found at 160 Torr (21 300 Pa). The discharge current ranged from 10 to 90 mA with the optimum current dependent on the pressure. A limit of detection of 0.8 pg was obtained for an Ar pressure of 160 Torr, a current of 70 mA, and an atomization temperature of 2000°C. This limit of detection is comparable to conventional GFAAS and a factor of five better than hollow cathode FANES (HC-FANES). The accuracy of the technique was assessed by the determination of Cr in a standard reference water (SRM 1643b).

Determination of nitrogen and oxygen and species containing nitrogen by molecular non-thermal excitation spectrometry (MONES) using microwave-induced plasma (MIP) and furnace atomization non-thermal excitation spectrometry (FANES) sources

A microwave-induced plasma (MIP) source produced through a surface-wave propagation process (surfatron) and a furnace atomization non-thermal excitation spectrometry source have been used to determine N and O in gaseous and aqueous samples, respectively, through the formation and emission of NH and OH radicals. Water is removed through liquid nitrogen cold trapping and hydrogen is added to the He plasma gas. The spectral characteristics of the two sources have been compared.

Investigations on the determination of chloride and bromide by furnace atomic non-thermal excitation spectrometry and furnace ionic non-thermal excitation spectrometry

The determination of chloride and bromide by non-thermal excitation spectrometry in a graphite furnace using both atomic and ionic spectral lines was investigated. The most sensitive determinations could be made at the ionic lines Cl II 479.545 nm and Br II 470.486 nm. The addition of an ionization buffer provided constant plasma conditions resulting in improved linearity of the calibration function. Under optimum conditions and in the presence of appropriate buffers detection limits of 0.6 ng for chloride and 2 ng for bromide were obtained.

Tandem sources using electrothermal atomizers: analytical capabilities and limitations

Tandem emission sources with electrothermal volatilization and atomization of the sample, such as furnace atomic non-thermal excitation spectrometry (FANES) or furnace atomization plasma emission spectrometry, are compared with other excitation sources, e.g., an inductively coupled plasma. The interdependence between the excitation and atomization processes, which causes restrictions for analytical procedures, is considered. Of particular interest for the analytical applications of tandem sources is the influence of matrix constituents on the excitation conditions. Furnace atomizers are able to form relatively high matrix concentrations in the excitation plasma, which can lead to a breakdown of the initial electron energy distribution. Correspondingly, depression of the analytical signals by the matrix has been found for FANES, which leads to some general conclusions on tandem sources.

Application of furnace atomic non-thermal excitation spectrometry for the determination of non-metals

Various atomic spectrometry techniques are used for the determination of elemental concentrations in a wide range of samples. Although procedures for the determination of metallic impurities are well established, the development of successful methods for the measurement of non-metal elements at trace levels has proved more difficult. In particular, better methods are required for the determination of B, Cl, P, S, Si, etc., in industrial and clinical samples.

The microwave enhanced bolometer: A cryogenic particle detector with large gain

A cryogenic detector is proposed which is a combination of the thermal calorimeter and the nonthermal superconducting detector: a bolometer crystal covered with a superconducting film. The detector is exposed to microwaves with an energy less than the Cooper pair breaking energy of the superconducting film. The primary excitations of the detector are the nonthermal phonon excitations produced by the interaction of a particle with the crystal. Those phonons are absorbed in the superconducting film and produce excess quasiparticles, which absorb the microwaves. The quasiparticles then de-excite by emission of low energy phonons which heat up the crystal. The detector signal is the temperature rise of the crystal. Because a quasiparticle can absorb many microwave photons during its long lifetime, more energy can flow into the bolometer than originally deposited by the energetic particle. The detector is basically a bolometer where the deposited energy is actively thermalized and amplified. Ultimately, the energy resolution of this detector is limited by the gain fluctuation, which is determined by the Poisson limited uncertainty in the number of excess quasiparticles.

Determination of traces of sulphur by electrothermal evaporation and non-thermal excitation of S-containing species in a hollow cathode discharge (FANES/MONES) and in a microwave induced plasma (MIP)

The determination of sulphur by emission of S-atoms, S+ ions, S2 and CS molecules using sulphate and other ions was investigated in such non-thermal excitation sources as the normal atmospheric argon-MIP and glow discharge in FANES/MONES (Furnace Nonthermal Excitation Spectrometry/Molecular Nonthermal Excitation Spectrometry). In both cases electrothermal evaporation (ETE) of the sample is applied. In the MIP technique (ETE-MIP) electrothermal evaporation from a new tungsten coil system is used and in the FANES samples are brought in the furnace. The thermal, electrical, chemical and pressure conditions were optimized and the emission spectra recorded. Detection limits are 90 ng for the ETE-MIP technique using the S 469.413 nm atom line. With the tungsten tube-FANES/MONES detection limits of 17 ng are obtained with S2 molecular band at 383.73 nm. With FANES/MONES in a carbon tube and measurements on CS molecular bands a detection limit of 2 ng is obtained.

UV Tunable Laser Ablation of YBa2Cu3Ox+6: Changes in the Product Population and Kinetic Energy Distributions as a Function of the Laser Wavelength and Target Bulk Temperature

ABSTRACTWe have conducted two separate experiments in the UV laser ablation of a sintered Yba2Cu3Ox+6wafer. We have measured the photoejected population distributions using selected UV laser wavelengths (4.01, 4.17 and 4.35 eV) near the 4.1 eV optical transition in Yba2Cu3Ox+6 In addition, we have measured the change in the ejected species kinetic energy as a function of the target bulk temperature. All the experiments were conducted at laser fluences well below the plasma formation threshold, and near that for product formation. Our results show that the UV laser ablation, at threshold fluences, proceeds via a nonthermal electronic excitation mechanism.

Analytical applications of furnace atomic non-thermal excitation spectrometry (FANES) and molecular non-thermal excitation spectrometry (MONES). Part. 5. Study of the MONES of PO and HPO for the determination of trace amounts of phosphorus

A method for the determination of phosphorus by the molecular non-thermal excitation spectrometry (MONES) of PO and HPO has been developed. The phosphorus was introduced into the furnace atomic non-thermal excitation spectrometry (FANES) source as a solution of sodium dihydrogen phosphate. The measurements were carried out at the bands that gave the maximum signals, for PO at 246.4 nm and for HPO at 507 nm. The electrical, thermal and chemical conditions were optimised and are discussed. In addition, the influence of La3+ as a chemical modifier on the MONES of PO and HPO was investigated. The best values for the detection limit were 700 pg of P (MONES of PO) and 3400 pg of P (MONES of HPO). By comparison with the best values obtained with commercial electrothermal atomisation atomic absorption spectrometry instruments, these values are better by factors of 8 and 1.6, respectively. However, the determination of P by FANES at 213.5/213.6 nm is the best method for investigations of phosphorus using the FANES source, in the presence of La3+ as a chemical modifier.

Furnace atomic non-thermal excitation spectrometry with the furnace as a hollow anode

Furnace atomic non-thermal excitation spectrometry with the furnace as the hollow anode (HA-FANES) was characterised for the determination of Cd and Cu. Operating in the abnormal glow discharge region, the current was limited by the current density at the cathode. Higher currents were attained with a larger diameter cathode and at higher pressures. The emission signals were dependent on the current density. More intense signals were observed when viewing the top and left of the discharge. This positional dependence of the signal strength was much more pronounced for Cu than for Cd. Peak areas and signal to noise ratios increased linearly with the discharge pressure to a maximum of 25.3 kPa. Emission intensities were constant as a function of the discharge current above a threshold of 20 mA for Cd and 50 mA for Cu. Both Cd and Cu gave the largest peak areas at the lowest atomisation temperature (1390 °C). The peak areas decreased roughly in proportion to the increased diffusion coefficients at higher temperatures. The detection limits for HA-FANES (0.8 and 1.5 pg for Cd and Cu, respectively) are comparable to those for conventional FANES with the furnace as a hollow cathode and graphite furnace atomic absorption spectrometry.

Energy transfer and photochemistry on a metal surface: Mo(CO)6 on Rh(100)

The occurrence of photoinduced reactions on solid surfaces depends on the relative rates between the excited-state decomposition and the energy transfer to the surface. In this study, the photodecomposition of Mo(CO)6 on Rh(100) at 90 K by 325-nm UV irradiation has been studied as a function of coverage and surface preparation using thermal desorption spectroscopy, electron energy-loss spectroscopy, and photoinduced desorption spectroscopy. It is found that Mo(CO)6 adsorbs dissociatively on Rh(100) into carbonyl fragments and CO in the first monolayer and molecularly in multilayers. Photoinduced desorption of CO is observed for the multilayers adsorbed onto the dissociated first layer via a nonthermal electronic excitation of adsorbed metal carbonyls. The presence of the metal surface prevents complete decarbonylation as in the gas phase; deexcitation of electronically excited carbonyls is not sufficiently fast to quench all the observed photochemistry. It is also found that Mo(CO)6 adsorbs molecularly on a presaturated CO ordered overlayer on Rh(100) and undergoes photodissociation to a greater degree than on the dissociated and disordered surface of carbonyl fragments. The ordered CO layer effectively screens the interaction between the molecular carbonyls and the Rh(100) layer surface.

Analytical applications of furnace atomic non-thermal excitation spectrometry (FANES) and molecular non-thermal excitation spectrometry (MONES). Part 4. Determination of trace amounts of phosphorus by FANES

A method of determining phosphorus by furnace atomic non-thermal excitation spectrometry (FANES) has been developed. The phosphorus is introduced into the FANES source as a solution of sodium dihydrogen phosphate. The measurements are carried out at 213.5/213.6 and 253.3/253.5 nm, the transition at 213.5/213.6 nm being the more sensitive one. The thermal and chemical conditions were optimised, the best chemical modifier being La3+ ions as they stabilise phosphate ions as LaPO4. Using the optimum amount of lanthanum (2 µg) the pre-treatment temperatures could be increased considerably (300 to 800 °C at normal pressure and 350 to 400 °C at low pressure). The best detection limit obtained is 90 pg of phosphorus, which is an improvement by a factor of 60 in comparison with the best values obtained with commercially available electrothermal atomisation atomic absorption spectrometric (ETAAS) instruments. Examples for real analyses with associated matrix interferences are given.

Theory and practical results of fluctuation analysis of transient signals in atomic emission spectroscopy with particular reference to furnace atomic nonthermal emission spectroscopy

In the course of development and approbation of Furnace Atomic Nonthermal Excitation Spectroscopy (FANES) comprehensive fluctuation analysis is important for the investigation of the compromise conditions of this emission source. The following investigations were made. (i) Determination of background noise and its dependence on the relevant variables of FANES, (ii) Determination of the functional dependence of fluctuations of the transient signal on the concentration of particular elements, (iii) Identification of noise components through calculations according to a well-known theory. The results show that the optical conductance of the spectrometer used has to be improved, especially for the wavelength range below 210 nm, in order to fully exploit the potential detection power of FANES.

Non-thermal rotational and vibrational excitation of CN produced in the flash photolysis of thiazole

In the flash photolysis of thiazole at low pressure without any diluent, the 0–0, 1–1 and 0–1 bands of the CN violet system were observed in absorption; the 0–0 band at 3883·4 A showed a high rotational excitation corresponding to a temperature of ⋍2000 K. The addition of argon makes the NCS bands appear with good intensity and at the same time relaxes the CN rotationally and vibrationally. These observations suggest that highly excited NCS is initially formed in the photodecomposition of thiazole which acted as a precursor to the rotationally and vibrationally excited CN radical. This paper deals with studies on the effect of argon on the relative intensities of CN and NCS and on the non-thermal rotational and vibrational intensity distribution of the CN violet system. The mechanism of formation of rotationally unrelaxed CN in the flash photolysis of thiazole has been proposed.

Contributions to biological analysis by atomic spectrometry — A summary of the achievements of Professor John Michael Ottaway

John Ottaway was the head of the Analytical Chemistry Research Group at the University of Strathclyde for almost 20 years and during that period much of the research performed by the Group was devoted to the development of improved analytical procedures for the determination of trace metals in clinical and biological samples. Although this was only one aspect of the Group's activities in analytical chemistry, a number of significant contributions were made in the clinical field and a summary of Professor Ottaway's achievements is given in this brief review. The techniques covered include electrothermal atomisation atomic absorption spectrometry (ETA-AAS), electrothermal atomisation atomic emission spectrometry (ETA-AES), furnace atomic non-thermal excitation spectrometry (FANES), continuum source atomic absorption spectrometry (CSAAS) and atomic fluorescence spectrometry (AFS).

Analytical applications of furnace atomisation non-thermal excitation spectrometry (FANES) and molecular non-thermal excitation spectrometry (MONES). Part 3. Determination of rare earth elements by electrothermal atomisation atomic emission spectrometry (ETA-AAS), FANES and furnace Ionisation non-thermal excitation spectrometry (FINES)

The application of two methods of trace analysis of microsamples, electrothermal atomisation atomic absorption spectrometry (ETA-AAS) and furnace atomisation non-thermal excitation spectrometry (FANES) to rare earth elements (REE) was studied. The evaporation and atomisation could be improved in both methods by the introduction of a tungsten platform into the graphite tubes to prevent the formation of REE carbides. Depending on the boiling-points of the REE, the absolute detection limits for both methods are in the picogram range. The thermal conditions for evaporation and atomisation were optimised. It was found that in ETA-AAS only the use of maximum heating conditions is successful. In FANES determinations on pure solutions the heating conditions can be reduced with the use of a vacuum, but in the presence of inorganic matrices it is again advantageous to use maximum heating. A new variation of FANES, furnace ionisation non-thermal excitation spectrometry (FINES), was developed for easily ionisable elements and was applied successfully to the determination of Eu, Sc and Sm. The limits of determination of REE in other REE are 1–100 p.p.m., depending on the conditions used, which were mainly influenced by the volatility of the elements.

Analytical applications of furnace atomisation non-thermal excitation spectrometry (FANES) and molecular non-thermal excitation spectrometry (MONES). Part 2. Determination of technetium-99 by FANES and electrothermal atomisation atomic absorption spectrometry

The determination of trace amounts of 99Tc was performed using electrothermal atomisation atomic absorption spectrometry (ETA-AAS) and furnace atomisation non-thermal excitation spectrometry (FANES). The thermal and chemical conditions were optimised. Tube-wall atomisation and matrix modification with 0.05 M Ni(NO3)2 in 0.1 M HNO3[forming Ni(TcO4)2] gave the best analytical results. The detection limits for 99Tc were 85 and 90 pg by ETA-AAS and FANES, respectively.

Multivariate optimisation of simultaneous multi-element analysis by furnace atomic non-thermal excitation spectrometry (FANES)

For the simultaneous determination of Ni, Co, Cu and Cr by furnace atomic non-thermal excitation spectrometry (FANES), the optimum atomisation temperature Tat, gas discharge pressure pAr and discharge current iHK of the FANES emission source with respect to the signal to noise ratio (SNR) are determined. As the maximum values of each of the SNRs are not achieved simultaneously, a statistical optimisation method including both grid search and differential extreme value evaluation is applied to the compromise conditions.