Atom Reservoir Research Articles

Spectroscopic and Kinetic Studies of the ClSO Radical from Cl2SO Photolysis.

Thionyl chloride (Cl2SO) serves as a common Cl atom source in widespread applications of chlorine chemistry though little is known about the reactivity and spectroscopy of the ClSO radical after a Cl-S bond cleavage. We performed a Pulsed Laser Photolysis experiment to detect ClSO from Cl2SO photolysis at 248 nm in a gas-flow reactor by time-resolved UV-vis transient absorption spectroscopy. A few chemical tests, using I2 and NO2, suggested the structured absorption band between 260 and 320 nm belonged to ClSO radical and that the termolecular ClSO + Cl + M → Cl2SO association reaction occurred. From EOMIP-CCSD/ano-pVQZ calculations, the ClSO band was assigned to the 12A″ ← X2A″ transition involving the π* ← π transition of the SO bond and the vibrational progression to the SO stretching mode of the 12A″ state, with a maximum cross-section = (2.0 ± 0.5) × 10-18 cm2 near 286 nm (1σ uncertainty) and an average spacing of vibrational structure of 658 cm-1. The rapid decay of the ClSO signal monitored near 303 nm could be fit to a second-order kinetic model over 10-90 Torr, which yields an effective bimolecular rate coefficient kCl+ClSO = (1.48 ± 0.42) × 10-11 cm3 molecule-1 s-1 at 292 K and 90 Torr (1σ uncertainty). This fast recombination reaction suggests that Cl-containing SOx species might act as significant Cl atom reservoirs in sulfur oxide-rich environments such as Venus' atmosphere. Moreover, the reported UV spectrum provides a new means for monitoring the ClSO radicals.

Tailoring the thermalization time of a cavity field using distinct atomic reservoirs

We study how the thermalization time of a single radiation cavity-field mode changes drastically depending on the type of the atomic reservoir it interacts. Temporal evolution of the field is analyzed within the micromaser scheme, where each atomic reservoir is modeled as a beam of atoms crossing an electromagnetic cavity in which they weakly interact with the field. The cavity-field thermalizes when we consider either multi-atom or multi-level atom reservoirs. We found that each atomic reservoir generates a different scaling law in the thermalization time of the cavity-field. Such scaling laws can be used for a faster or slower heating and cooling process. We have obtained analytical expressions for the thermalization time that were verified by means of a numerical simulation of the injection of each atomic reservoir into the cavity. We also discussed how our results could boost the efficiency and power output of some quantum heat engines during a finite time operation when the radiation field mode acts as the working substance.

Alloy-assisted deposition of three-dimensional arrays of atomic gold catalyst for crystal growth studies

Large-scale assembly of individual atoms over smooth surfaces is difficult to achieve. A configuration of an atom reservoir, in which individual atoms can be readily extracted, may successfully address this challenge. In this work, we demonstrate that a liquid gold–silicon alloy established in classical vapor–liquid–solid growth can deposit ordered and three-dimensional rings of isolated gold atoms over silicon nanowire sidewalls. We perform ab initio molecular dynamics simulation and unveil a surprising single atomic gold-catalyzed chemical etching of silicon. Experimental verification of this catalytic process in silicon nanowires yields dopant-dependent, massive and ordered 3D grooves with spacing down to ~5 nm. Finally, we use these grooves as self-labeled and ex situ markers to resolve several complex silicon growths, including the formation of nodes, kinks, scale-like interfaces, and curved backbones.

Combinatorial effects on clumped isotopes and their significance in biogeochemistry

The arrangement of isotopes within a collection of molecules records their physical and chemical histories. Clumped-isotope analysis interrogates these arrangements, i.e., how often rare isotopes are bound together, which in many cases can be explained by equilibrium and/or kinetic isotope fractionation. However, purely combinatorial effects, rooted in the statistics of pairing atoms in a closed system, are also relevant, and not well understood. Here, I show that combinatorial isotope effects are most important when two identical atoms are neighbors on the same molecule (e.g., O2, N2, and D–D clumping in CH4). When the two halves of an atom pair are either assembled with different isotopic preferences or drawn from different reservoirs, combinatorial effects cause depletions in clumped-isotope abundance that are most likely between zero and −1‰, although they could potentially be −10‰ or larger for D–D pairs. These depletions are of similar magnitude, but of opposite sign, to low-temperature equilibrium clumped-isotope effects for many small molecules. Enzymatic isotope-pairing reactions, which can have site-specific isotopic fractionation factors and atom reservoirs, should express this class of combinatorial isotope effect, although it is not limited to biological reactions. Chemical-kinetic isotope effects, which are related to a bond-forming transition state, arise independently and express second-order combinatorial effects related to the abundance of the rare isotope. Heteronuclear moeties (e.g., CO and CH), are insensitive to direct combinatorial influences, but secondary combinatorial influences are evident.In general, both combinatorial and chemical-kinetic factors are important for calculating and interpreting clumped-isotope signatures of kinetically controlled reactions. I apply this analytical framework to isotope-pairing reactions relevant to geochemical oxygen, carbon, and nitrogen cycling that may be influenced by combinatorial clumped-isotope effects. These isotopic signatures, manifest as either directly bound isotope “clumps” or as features of a molecule’s isotopic anatomy, are linked to molecular mechanisms and may eventually provide additional information about biogeochemical cycling on environmentally relevant spatial scales.

Observation of quantized conductance in neutral matter.

In transport experiments, the quantum nature of matter becomes directly evident when changes in conductance occur only in discrete steps, with a size determined solely by Planck's constant h. Observations of quantized steps in electrical conductance have provided important insights into the physics of mesoscopic systems and have allowed the development of quantum electronic devices. Even though quantized conductance should not rely on the presence of electric charges, it has never been observed for neutral, massive particles. In its most fundamental form, it requires a quantum-degenerate Fermi gas, a ballistic and adiabatic transport channel, and a constriction with dimensions comparable to the Fermi wavelength. Here we report the observation of quantized conductance in the transport of neutral atoms driven by a chemical potential bias. The atoms are in an ultraballistic regime, where their mean free path exceeds not only the size of the transport channel, but also the size of the entire system, including the atom reservoirs. We use high-resolution lithography to shape light potentials that realize either a quantum point contact or a quantum wire for atoms. These constrictions are imprinted on a quasi-two-dimensional ballistic channel connecting the reservoirs. By varying either a gate potential or the transverse confinement of the constrictions, we observe distinct plateaux in the atom conductance. The conductance in the first plateau is found to be equal to the universal conductance quantum, 1/h. We use Landauer's formula to model our results and find good agreement for low gate potentials, with all parameters determined a priori. Our experiment lets us investigate quantum conductors with wide control not only over the channel geometry, but also over the reservoir properties, such as interaction strength, size and thermalization rate.

Time-resolved laser-induced saturated fluorescence measurements in a thallium see-through hollow cathode discharge: Evaluation of ground state number density and quantum efficiency

A thallium see-through hollow cathode lamp, or galvatron, was studied to evaluate its potential as a narrow band atomic line filter. Time-resolved laser-induced saturated fluorescence was used to evaluate the ground state number density of this glow discharge as a function of current. It was found to produce a sufficient number density at 16.0 mA to absorb 99.9% of incident light from a line source based on an absorption curve-of-growth calculation. A saturation curve was experimentally obtained and modeled with a time-dependent two-level model, as well as a time-dependent three-level model in the presence of a trap. The three-level model showed excellent agreement with the experimental data when a 10 ns pulse duration was used and when collisional rate constants were set to zero. The quantum efficiency of the system was found to be limited only by the spontaneous transition probabilities. Evaluation of these two parameters has shown that a thallium galvatron is an attractive atom reservoir for the applications as a narrow band atomic line filter.

Atom laser dynamics in a tight waveguide

We study the transient dynamics that arise during the formation of an atom laser beam in a tight waveguide. The time dependent density profile develops a series of wiggles which are related to the diffraction in time phenomenon. The apodization of matter waves, which relies on the use of smooth aperture functions, allows to suppress such oscillations in a time interval, after which there is a revival of the diffraction in time. The revival time scale is directly related to the inverse of the harmonic trap frequency for the atom reservoir.

High-resolution Fabry–Pérot interferometric emission measurements of the 535.046 nm thallium line in a see-through hollow cathode discharge

A thallium see-through hollow cathode lamp, or galvatron, is investigated for applications as a narrow band atomic line filter. In order to determine the resolving power of this atom reservoir, high resolution emission profile measurements of the 535.046 nm line were obtained by a scanning Fabry–Perot interferometer coupled to a spectrometer. The resulting spectra are modeled by a two-layer model which takes into account line broadening due to self-absorption and allows the calculation of the Doppler temperature and optical depths of the two layers. The results obtained for the galvatron are compared to a traditional thallium hollow cathode lamp and a thallium electrodeless discharge lamp. The galvatron was found to produce Doppler temperatures from 495 K to 630 K from currents of 10.0 mA to 30.0 mA, respectively, which were lower than the values found from the traditional hollow cathode lamp at similar currents. These results make this atomic reservoir attractive for applications as an atomic line filter.

New plasma discharges for atomic spectrometry

Scientific innovation in analytical atomic spectrometry, one of the oldest instrumental methods of chemical analysis, has always depended on the development of new sources, the improvement of existing ones, or the development of novel spectrometers optimized for the sources of interest. This holds true for sample introduction (and atomisation), signal generation (excitation, ionisation, fluorescence, scattering), signal dispersion and detection, regardless of whether we are considering optical or mass spectrometry. The modern atomic spectroscopy era began in the early 1950s due to the development of (electric) flames, arcs and sparks, and it was the focus of many investigations, where furnaces were used as atom reservoirs for atomic absorption studies. Glow discharges were applied as powerful atomic emission spectrometry sources in direct solid and layer analyses performed in the early 1970s. More recently, high-frequencyand microwave-induced plasmas were used for elemental trace analysis, and these were found to be particularly useful in speciation studies where it was coupled on-line with different kinds of chromatography. Further impetus to this field of study was provided by coupling plasma discharges to elemental mass spectrometry [1]. New sources of innovation are also arising from the growing need to obtain better detection limits, especially when it comes to elemental determinations in the smallest compartments, as required in the biomedical and nanosciences, as well as from the demands for miniaturization, such as the drive to produce smaller devices for field-monitoring or process analysis, or simply a new requirement for dedicated instrumentation. All of these impulses are driving forces for novel research in the area of plasma discharges. Additionally, as known from the field of plasma-related science, the many ways to generate plasma sources are far from being fully exploited analytically, and the fundamentals of conventional sources, which are already in practical use, are far from being completely understood. Also, theoretical modelling is not or is rarely available, analytical performance is often not optimized in routine applications, and reliable hardware (for instance, hardware used for sample introduction) and affordable consumables are lacking. There are thus many reasons why improvements are needed in plasma-based spectroscopy, and why a special issue that focussed on the three following areas, where new trends and innovations were noted by the guest editors, was organized:

Some trends in the development of microplasmas for spectrochemical analysis.

The development of microplasmas for spectrochemical analysis by optical methods is discussed. Recent achievements in miniaturization are highlighted, especially for three types of plasmas, namely high-frequency plasmas, dc-discharges and microwave plasmas. The potentials of each of these groups of plasmas as sources for atomic emission spectrometry are discussed. Literature citations and experiments indicate that the plasmas are also very useful as atom reservoirs for atomic absorption spectrometry. Methods of sampling, including feeding with gas chromatography effluents, the use of electrothermal vaporization, and the evolution of gaseous species (as shown for the case of Hg vapor), are discussed as prominent interfaces to make use of these sources for elemental analysis.

The development of microplasmas for spectrochemical analysis

Miniaturized microwave, high-frequency, and dc-powered microplasmas are discussed, with emphasis on the state-of-the-art and development trends. Specific atomic emission sources discussed include the microstrip microwave plasma operated in argon and helium at ca 10-30 W and below 1 L min(-1) gas at atmospheric pressure, the capacitively coupled microplasma, operated at 13.56 MHz, 5-25 W, and 17-150 mL min(-1) helium, the miniaturized inductively coupled plasma operated at several watts and reduced pressure, and dc glow-discharge plasmas on a chip, including a barrier-layer discharge as atom reservoir for atomic absorption spectrometry. Diagnostics for these sources are discussed and some of their figures of merit are compared with those of conventional sources. Current possibilities for introduction of gaseous samples are reported and scope for further development and outlook are both discussed.

Laser-enhanced ionization: recent developments

Initially developed for the analysis of simple aqueous solutions, laser-enhanced ionization (LEI) is a very sensitive trace analysis technique which is based on the spectrally selective laser excitation of analyte atoms followed by their collisional ionization and detection in a suitable atom reservoir. Its unique versatility, granted by a rich choice of excitation wavelengths, and its high efficiency of charge creation and collection make LEI one of the most sensitive techniques for elemental analysis. Despite these attractive features, LEI has not been widely used for the chemical analysis of liquid and solid samples having more complex matrices. This article describes the current limitations of LEI and recent achievements in the ongoing development of this promising technique.

Laser-enhanced ionization: recent developments

Initially developed for the analysis of simple aqueous solutions, laser-enhanced ionization (LEI) is a very sensitive trace analysis technique which is based on the spectrally selective laser excitation of analyte atoms followed by their collisional ionization and detection in a suitable atom reservoir. Its unique versatility, granted by a rich choice of excitation wavelengths, and its high efficiency of charge creation and collection make LEI one of the most sensitive techniques for elemental analysis. Despite these attractive features, LEI has not been widely used for the chemical analysis of liquid and solid samples having more complex matrices. This article describes the current limitations of LEI and recent achievements in the ongoing development of this promising technique.

Novel uses of lasers in atomic spectroscopy

This paper reviews several novel uses of lasers in atomic spectroscopy. A tutorial discussion is given of the basic processes involving the interaction of laser radiation with atoms and the measurement approaches. Laser microprobes, especially laser induced breakdown spectroscopy and laser ablation-inductively coupled plasma-optical emission or mass spectrometry are reviewed thoroughly with respect to principles, instrumentation and applications. Laser excited atomic fluorescence and atomic absorption spectrometry with diode lasers are considered primarily with respect to recent publications. Laser-enhanced ionization, resonance ionization and resonance ionization imaging are also thoroughly reviewed with respect to recent publications. Diagnostical measurements of plasmas and atom reservoirs are discussed. The principles of six laser based atomic absorption methods are given and the methods are compared with respect to detection limits. Finally, future uses of lasers in atomic spectroscopy and a comparison of the characteristics of various atomic methods for trace elements are given.

A Miniature Glow Discharge for Laser Excited Atomic Fluorescence Detection of Lead

A miniature glow discharge atom reservoir has been designed for laser excited atomic fluorescence spectrometric measurements of nanoliter-sized solution residues. A copper vapor laser pumped dye laser was used to measure the fluorescence of Ph atoms sputtered from the Ni cathode of the discharge. Excitation of Pb occurred at 283.3 nm, and fluorescence was monitored at 405.8 nm. The optimal discharge operating pressure and current were 5.5 Torr and 20 mA with continuous fill gas introduction. No improvement was found in S/N with stop flow versus flowing operation; however, considerable improvement in the S/N was achieved when gated peak integration, in contrast to peak detection, was employed. The temporal profiles indicated that the Pb atoms were rapidly sputtered from the surface of the cathode and that a high percentage of these atoms diffused back toward the cathode. The redeposition of the Pb atoms led to peak tailing with signals lasting more than 60 s. In effect, atoms were sputtered, atomized, and excited several times during a measurement. The limit of detection for Pb was 0.6 pg based on peak detection and 0.03 pg based on peak area measurements. These detection limits were several orders of magnitude higher than the theoretical, intrinsic detection Limit due to the interfering background emission of molecular impurities, such as N 2 and H 2O, present in the discharge.

Glow Discharge Atomic Spectroscopy

Glow discharge sources (GDSs) have long been used in atomic spectrometry. In particular, they are recognized as sources for atomic emission research in connection with the early work of Paschen with hollow cathodes, which later were studied in detail as the primary sources for atomic absorption work. In its initial stage, glow discharge analytical emission spectrometry also made use mainly of hollow cathodes, which became widespread for the determination of very low absolute concentrations of all elements including most nonmetals. However, for routine analysis of compacted metal samples, the break-through first occurred at the end of the sixties with the work of Grimm, who introduced a restricted GDS in which flat samples were directly mounted as a cathode. As an atomic emission device, the source became widespread in industry for bulk and especially for depth-profiling purposes. Also, for atomic absorption and atomic fluorescence work, GDSs proved to be very valuable as atom reservoirs, and the appropriate analytical techniques were developed.

Laser-Excited Atomic Fluorescence of Eu, Y, and Tm in a Miniature Glow Discharge Atom Reservoir

A miniature glow discharge (GD) is evaluated as an atom reservoir for laser-excited atomic fluorescence spectrometric measurements of Eu, Y, and Tm. Nanoliter-sized aqueous samples are deposited and dried on the Ni cathode and atomized upon ignition of the GD. The atom population is probed by a copper vapor laser pumped dye laser, and direct-line fluorescence is detected. The optimum chamber pressures and operating currents are 1 Torr and 10 mA for Eu, 2 Torr and 10 mA for Y, and 3 Torr and 40 mA for Tm. The fluorescence temporal profiles are found to consist of short (∼20-ms duration) transient spikes, followed by long tails which last more than 60 s as a result of sample redeposition on the cathode surface. The limits of detection (3a) are 2 fg, 1.2 pg, and 0.08 fg for Eu, Y, and Tm, respectively, with the use of signal area integration over a 6-s duration. Theoretically simulated signals for a particular sample mass, considering the geometry of the GD atomizer, were found to fall within one order of magnitude of those obtained by experiment.

Thermodynamics of benzylic C–H activation in 18- and 19-electron iron sandwich complexes: determination of pKavalues and bond dissociation energies

The pKa values and bond dissociation energies of 19-electron complexes have been determined for the first time, supporting the concept of proton and hydrogen atom reservoirs for late transition-metal sandwich complexes.

A profile of Jim Winefordner including a bibliography and a list of co-workers

THERE are many qualitative and quantitative measures which one might use to examine a scientific career. During his 35 years at the University of Florida, Jim Winefordner has provided data for many. Perhaps the most interesting and informative measure of any scientist’s career lies in the publication record. Jim’s bibliography, at present containing some 725 publications, is included in this special issue. The sheer quantity of publication is remarkable. On average, Jim has produced a paper every 18 days for 35 years. These have been distributed among some 57 scientific journals with about 95 papers appearing in Spectrochimicu Actu B. It provides a panoramic view of his scientific interests. With few exceptions, his work falls under the broad umbrella of spectrochemistry and, within that domain, there is almost no technique to which he has not made some important contribution. Some of his favorite interests are obvious. I doubt that anyone has published or ever will publish as many papers on atomic fluorescence spectrometry. Jim was the first to use atomic fluorescence as an analytical method; his first paper on the subject appeared in 1964. About a third of Jim’s bibliography is devoted in some way to atomic fluorescence. He has considered theoretical aspects, experimental nuances and a multitude of practical applications. Every conceivable experimental permutation has been studied with many different excitation sources, atom reservoirs and detection systems. Atomic fluorescence investigations continue to form the backbone of Jim’s still vigorous research program. He quickly recognized the role that lasers could play in analytical spectroscopy and was among the first to use a pulsed dye laser as an excitation source. Laser excitation figured prominently in his atomic fluorescence work as well as in a multitude of other spectroscopic studies. Jim has shown a persistent interest in every facet of luminescence spectrometry, including molecular techniques such as low temperature and room temperature phosphorescence and fluorescence in various media and surface enhanced Raman spectrometry. Naturally, this work led to many side trips, especially into studies of a more fundamental kind. Distributed throughout the bibliography are papers addressing characterization of flames and plasmas, development of methods for plasma diagnostics, measurements of free atom fractions, temperature measurements, luminescence lifetimes, etc. Jim has always been interested in the validity of analytical measurements and so there are many publications concerning the measurement and prediction of signal and noise and upon one of his favorite topics, the rigorous definition of a limit of detection. Jim’s work has played an important role in the widespread acceptance of a standard definition of the limit of detection. Jim has maintained this extraordinary level of research productivity by relying on hard work and a prodigious appetite for the scientific literature. Over the years he has methodically accumulated some 32,000 reprints and categorized them under 144 topics, filling 40 file drawers. Even though these are cross-indexed by author, the

Time-resolved fluorescence as a direct experimental approach to the study of excitation and ionization processes in different atom reservoirs

Several examples of laser-excited, time-resolved fluoresence waveforms are discussed to show how the essential parameters describing the interaction between the radiation and the atomic system can be directly evaluated. The results reported here have been experimentally obtained, with relatively fast detection electronics, in different atom reservoirs operated at atmospheric pressure, that is, an air-acetylene flame, an inductively coupled argon plasma and a graphite furnace. It is shown that the study of the complete temporal evolution (i.e., during and after excitation) of the population density of selected atomic levels, directly pumped by the laser or collisionally coupled to the laser-excited level, can provide important information about the dyamics of the interaction and the saturation behaviour of the transition as a function of the different atomization environments. In simple cases, collisional mixing and ionization rate coefficients can also be evaluated. The measurements discussed here have been obtained with the following elements: Au, Hg, Mg, Na, Pb, Sr and Tl. It is shown that the analytical relevance of the information gained from the waveforms is particularly significant when two or more lasers (i.e., excitation steps) are used in the techniques of Laser Induced Fluoresence (LIF) and Laser Enhanced Ionization (LEI) in flames and electrothermal atomizers.