Atomic structure and isotopes

The hydrogen atom has the simplest atomic structure of all elements and consists of a nucleus and one electron. A neutral H atom can join a second electron, which forms the negative ion, H. Atomic hydrogen is formed as a result of different chemical reactions, but its lifetime is extremely short, as the atoms join each other to form a 

The Hydrogen Economy Opportunities and Challenges, ed. Michael Ball and Martin Wietschel. Published by Cambridge University Press. Cambridge University Press 2009. 

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Hydrogen has three isotopes. The atomic structure and isotopic symbols for the three isotopes of hydrogen are shown in Figure 2.8. 

Nuclear properties (spins, moments, charge radii) revealed by the analysis of hyperfine structure and isotope shift of atomic levels have been obtained in decades of experiments. Since 1975 with the introduction of tunable dye laser, the rebirth of the methods, some already known since 1930, had led to many on line experiments on short lived isotopes not investigated before. I report here a sample of the experiments done by the Orsay, Mainz groups at CERN. Although experiments have been carried out by the Orsay group using the proton beam of the CERN Proton Synchrotron, most of the experiments have been done at Isolde, the on - line mass separator at CERN, whose radioactive beams are essential to the success of these experiments [RAV 84]. 

Temperature units/conversions Periodic table Basic atomic structure Quantum mechanical model Atomic number and isotopes Atoms, molecules, and moles Unit conversions Chemical equations Stoichiometric calculations Week 3 Atmospheric chemistry... 

Childs, W. J. and Goodman, L. S., "Hyperfine structure and isotope-shift measurements on Dy I 5988.562 using high-resolution laser spectroscopy and an atomic beam,"... 

Mass spectrographs were also built in the United States by A. J. Dempster and K. T. Bainbridge. The mass spectrograph has been succeeded by the mass spectrometer, in which the intensity of the separated ion beams are measured electrically. These instruments are now widely used in the determination of molecular structure (Chapter 13). The term relative atomic mass is now used in place of atomic weight, and isotopic masses are measured on the = 12.0000 scale. Aston himself soon discovered that small deviations from the whole-number rule are the norm. 

Many of the spectroscopic studies were performed to demonstrate the capability of the technique and of a number of variants which are specific for the combination of laser spectroscopy with fast beams of ions or atoms. An example has already been discussed in Section 3.3 Resonant two-photon exdtation becomes possible by adjusting the Doppler shifts for interaction with the direct and retroreflected laser beam to the atomic transition energies. Other features include the preparation of otherwise inaccessible atomic states, the separation of hyperfine structures from different isotopes by the Doppler shift, or the observation of time-resolved transient phenomena along the beam. The extensive research on nuclear moments and radii from the hyperfine structure and isotope shift constitutes a self-contained program, which will be discussed separately in Section 5. 

The motivation for hyperfine structure and isotope shift studies in the isoelectronic case of Ra II and in Ra I came originally from nuclear physics. After early measurements of the atomic energy levels on the long-lived Ra/ the isotope shifts and the hyperfine structures of the odd-A isotopes remained inaccessible until recentlyThe extraction of nuclear moments required the analysis of the electronic hyperfine fields which was performed in on-line collinear-beam studies of several transitions involving the 7s Si/2 and Ip Pi/2 states of Ra II and all states of the 7s7p configur-... 

Relation Between Atomic Structure and Natural Abundance of Elements and Isotopes 3... 

E. Matthias, H. Rinneberg, R. Beigang, A. Timmermann, J. Neukammer, K. Liicke Hyperfine structure and isotope shifts in alkaline earth atoms, in Atomic Physics 5, ed. by I. Lindgren, A. Rosen, S. Svanberg (Plenum, New York 1983) p.543... 

Studies of the volmne effect yield information on the charge distribution in the nucleus. Hyperfine structure and isotopic shifts are of the same order of magnitude. Isotopic shifts can be studied in the visible region as weU as in the X-ray region. Particularly prominent isotopic shifts are obtained for muonic atoms, in which, for example, a p meson (m = 209me) has taken the place of an electron. The classical radius of the orbit is reduced by a factor of 209, and thus the nuclear influences are much greater than those pertaining to the electrons. Isotope shifts and their interpretation have been discussed m [2.57-2.59J. 

HYPERFINE STRUCTURE AND ISOTOPE SHIFTS OF RYDBERG STATES IN ALKALINE EARTH ATOMS... 

The previous discussion has centered on how to obtain as much molecular mass and chemical structure information as possible from a given sample. However, there are many uses of mass spectrometry where precise isotope ratios are needed and total molecular mass information is unimportant. For accurate measurement of isotope ratio, the sample can be vaporized and then directed into a plasma torch. The sample can be a gas or a solution that is vaporized to form an aerosol, or it can be a solid that is vaporized to an aerosol by laser ablation. Whatever method is used to vaporize the sample, it is then swept into the flame of a plasma torch. Operating at temperatures of about 5000 K and containing large numbers of gas ions and electrons, the plasma completely fragments all substances into ionized atoms within a few milliseconds. The ionized atoms are then passed into a mass analyzer for measurement of their atomic mass and abundance of isotopes. Even intractable substances such as glass, ceramics, rock, and bone can be examined directly by this technique. 

Since detailed chemical structure information is not usually required from isotope ratio measurements, it is possible to vaporize samples by simply pyrolyzing them. For this purpose, the sample can be placed on a tungsten, rhenium, or platinum wire and heated strongly in vacuum by passing an electric current through the wire. This is thermal or surface ionization (TI). Alternatively, a small electric furnace can be used when removal of solvent from a dilute solution is desirable before vaporization of residual solute. Again, a wide variety of mass analyzers can be used to measure m/z values of atomic ions and their relative abundances. 

The SIMS analytical ion signal of a specific element or isotope also can be enhanced by selective ionization of particular atoms, and the detection limit for that element thereby improved. This mode of SNMS is important to specific applications, but it lacks the generality inherent in nonselective SNMS methods. The focus of this article will be on the methods for obtaining complete, accurate, and matrix-independent compositions of chemically complex thin-film structures and materials. 

This book presents a unified treatment of the chemistry of the elements. At present 112 elements are known, though not all occur in nature of the 92 elements from hydrogen to uranium all except technetium and promethium are found on earth and technetium has been detected in some stars. To these elements a further 20 have been added by artificial nuclear syntheses in the laboratory. Why are there only 90 elements in nature Why do they have their observed abundances and why do their individual isotopes occur with the particular relative abundances observed Indeed, we must also ask to what extent these isotopic abundances commonly vary in nature, thus causing variability in atomic weights and possibly jeopardizing the classical means of determining chemical composition and structure by chemical analysis. 

Our present views on the electronic structure of atoms are based on a variety of experimental results and theoretical models which are fully discussed in many elementary texts. In summary, an atom comprises a central, massive, positively charged nucleus surrounded by a more tenuous envelope of negative electrons. The nucleus is composed of neutrons ( n) and protons ([p, i.e. H ) of approximately equal mass tightly bound by the force field of mesons. The number of protons (2) is called the atomic number and this, together with the number of neutrons (A ), gives the atomic mass number of the nuclide (A = N + Z). An element consists of atoms all of which have the same number of protons (2) and this number determines the position of the element in the periodic table (H. G. J. Moseley, 191.3). Isotopes of an element all have the same value of 2 but differ in the number of neutrons in their nuclei. The charge on the electron (e ) is equal in size but opposite in sign to that of the proton and the ratio of their masses is 1/1836.1527. 

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