Radiation, atomic spectroscopy

Light is electromagnetic radiation to which the retina of the eye is sensitive, but electromagnetic radiation also includes regions identified as infrared, ultraviolet, x-ray, gamma-ray, and radiofrequency radiation. Atomic spectroscopy utilizes primarily the ultraviolet and visible regions of the electromagnetic spectrum. It is important therefore to understand some of the basic characteristics and properties of such radiation. 

Spectroscopy The science of analyzing the spectra of atoms and molecules. Emission spectroscopy deals with exciting atoms or molecules and measuring the wavelength of the emitted electromagnetic radiation. Absorption spectroscopy measures the wavelengths of absorbed radiation. 

Atomic spectroscopy. This spectroscopy gives results of interaction of electromagnetic radiation with atoms which are in their lowest energy state or ground state. 

In atomic spectroscopy, a substance is decomposed into atoms in a flame, furnace, or plasma. (A plasma is a gas that is hot enough to contain ions and free electrons.) Each element is measured by absorption or emission of ultraviolet or visible radiation by the gaseous atoms. To measure trace elements in a tooth, tiny portions of the tooth are vaporized (ablated) by a laser pulse1 and swept into a plasma. The plasma ionizes some of the atoms, which pass into a mass spectrometer that separates ions by their mass and measures their quantity. 

I n atomic spectroscopy, samples are vaporized at 2 000-8 000 K and decompose into atoms. Concentrations of atoms in the vapor are measured by emission or absorption of characteristic wavelengths of radiation. Because of its high sensitivity, its ability to distinguish one element... 

The besl isolation of radiant energy can he achieved with flame spectrometers that incorporate either a prism sir grating monochromator, those with prisms having variable gauged entrance and exii slits. Both these spectrometers provide a continuous selection of wavelengths with resolving power sufficient lo separate completely most of the easily excited emission lines, and afford freedom from scattered radiation sufficient lo minimize interferences. Fused silica or quartz optical components are necessary to permit measurements in Ihe ultraviolet portion of the spectrum below 350 nanometers Sec also Analysis (Chemical) Atomic Spectroscopy Photometers and Spectra Instruments. 

For many reasons atomic spectroscopy continues to be one of the most rapidly developing branches of physics. This is primarily due to the creation of very stable and monochromatic lasers, allowing one to selectively excite various atomic states, to create very highly excited (Rydberg) atoms, and due to the occurrence of new possibilities, given by non-atmospheric astrophysics, which allow one to register the electromagnetic radiation... 

In stellar astronomy, spectroscopic studies are indirectly revealing the structure deep down in stars where one could not see otherwise. An internal structure shows up in the emergent radiation spectrum both kinematically and through abundance anomalies. The solution of the solar corona line problem in 1942 may serve as a typical example of astrophysical applications of atomic spectroscopy [256]. 

This monograph presents a complete, up-to-date guide to the theory of modern spectroscopy of atoms. It describes the contemporary state of the theory of many-electron atoms and ions, the peculiarities of their structure and spectra, the processes of their interaction with radiation, and some of the applications of atomic spectroscopy. 

R. Schinke Photodissociation Dynamics 2. L. Frommhold Collision-Induced Absorption in Gases 3. T. F. Gallacher Rydberg Atoms 4. M. Auzinsh and R. Ferber Optical Polarization of Molecules 5.1. E. McCarthy and E. Weigold Electron-Atom Collisions 6. V. Schmidt Electron Spectrometry of Atoms using Synchrotron Radiation 7. Z. Rudzikas Theoretical Atomic Spectroscopy... 

The data of atomic spectroscopy are of extreme importance in revealing the nature of quantum-electrodynamical effects. For the investigation of many-electron atoms and ions, it is of great importance to combine theoretical and experimental methods. Therefore, the methods used must be universal and accurate. A number of physical characteristics of the many-electron atom (e.g., a complete set of quantum numbers) may be found only on the basis of theoretical considerations. In many cases the mathematical modelling of physical objects and processes using modern computers may successfully replace the corresponding experiments. In this book we shall describe the contemporary state of the theory of many-electron atoms and ions, the peculiarities of their structure and spectra as well as the processes of their interaction with radiation, and some applications. 

Chemists study atoms by observing the properties of electromagnetic radiation they emit. They then build up a model of the structure of the atom that accounts for these properties. The analysis of the electromagnetic radiation emitted or absorbed by substances is a branch of chemistry called spectroscopy. We shall see that atomic spectroscopy—spectroscopy applied to atoms—can be used to determine their internal structure. 

Atomic spectrometry is based on the generation of free atoms which can absorb or emit radiation due to defined transitions of the valence electrons of the outer shell of the atom. Comprehensive and critical reviews of atomic spectroscopy and its uses appear in Journal of Analytical Atomic Spectrometry. Advances in AAS and fluorescence spectrometry have been reviewed by Hill et al. (1991). Branch etal. (1991) has updated the use of AS for the analysis of clinical and biological materials, foods and beverages and discussed methods for individual elements. Cresser et al. (1991, 1992) have reviewed environmental analysis, including those for soils and plants and have included summary tables of methods. 

Image Devices. Although he never assembled an actual TV-spectrometer, Margoshes was the first to recognize the potential of TV-type detectors in analytical atomic spectroscopy. In a series of reports (50,51,52) he speculated on the advantages of using an SEC tube [vide infra] to detect radiation dispersed by an echelle spectrograph. These reports and the recent availability of various solid-state array detectors have prompted numerous... 

Then in Chapter 3, before we come to the theory of molecular structure, we shall introduce you to the experimental techniques of finding out about molecular structure. This means studying the interactions between molecules and radiation by spectroscopy—using the whole electromagnetic spectrum from X-rays to radio waves. Only then, in Chapter 4, will we go behind the scenes and look at the theories of why atoms combine in the ways they do. Experiment comes before theory. The spectroscopic methods of Chapter 3 will still be telling the truth in a hundred years time, but the theories of Chapter 4 will look quite dated by then. 

The viewing region of the plasma can achieve a temperature of 5000-6000°C and is reasonably stable. The sample solution is aspirated into the core area between the two arms of the Y where it is atomised, excited and viewed. This technique keeps with the atomic spectroscopy theory in that the measurements are obtained by emission from the valence electrons of the atoms that are excited, and the emitted radiation consists of short well-defined lines. All these lines fall in the UV or VIS region of the spectrum and identification of these lines permits qualitative/quantitative detection of elements. 

In this chapter, we discuss the basic principles that are necessary to understand measurements made with electromagnetic radiation, particularly those deeding with the absorption of UV, visible, and IR radiation. The nature of electromagnetic radiation and its interactions with matter are stressed. The next four chapters are devoted to. spectroscopic instruments (Chapter 25), molecular absorption spectroscopy (Chapter 26), molecular fluorescence spectroscopy (Chapter 27), and atomic spectroscopy (Chapter 28). 

In atomic fluorescence spectroscopy, an external source is used just as in atomic absorption, as shown in Figure 24-6. Instead of measuring the attenuated source radiant power, however, the radiant power of fluorescence, Pp, is measured, usually at right angles to the source beam. In such experiments, we must avoid or discriminate against scattered source radiation. Atomic fluorescence is often measured at the same wavelength as the source radiation, in which case it is called resonance fluorescence. 

Line source In atomic spectroscopy, a radiation source that emits sharp atomic lines characteristic of the analyte atoms see hollow-cathode lamp and electrodeless discharge lamp. 

Atomic spectroscopy is the oldest instrumental elemental analysis principle, the origins of which go back to the work of Bunsen and Kirchhoff in the mid-19th century [1], Their work showed how the optical radiation emitted from flames is characteristic of the elements present in the flame gases or introduced into the burning flame by various means. It had also already been observed that the intensities of the element-specific features in the spectra, namely the atomic spectral lines, changed with the amount of elemental species present. Thus the basis for both qualitative and quantitative analysis with atomic emission spectrometry was discovered. These discoveries were made possible by the availability of dispersing media such as prisms, which allowed the radiation to be spectrally resolved and the line spectra of the elements to be produced. 

---