Rubidium optical spectra

Many elements are present in the earth s crust in such minute amounts that they could never have been discovered by ordinary methods of mineral analysis. In 1859, however, Kirchhoff and Bunsen invented the spectroscope, an optical instrument consisting of a collimator, or metal tube fitted at one end with a lens and closed at the other except for a slit, at the focus of the lens, to admit light from the incandescent substance to be examined, a turntable containing a prism mounted to receive and separate the parallel rays from the lens and a telescope to observe the spectrum produced by the prism. With this instrument they soon discovered two new metals, cesium and rubidium, which they classified with sodium and potassium, which had been previously discovered by Davy, and lithium, which was added to the list of elements by Arfwedson. The spectroscopic discovery of thallium by Sir William Crookes and its prompt confirmation by C.-A. Lamy soon followed. In 1863 F. Reich and H. T. Richter of the Freiberg School of Mines discovered a very rare element in zmc blende, and named it indium because of its brilliant line in the indigo region of the spectrum. 

Rubidium was discovered in 1861 by Bunsen and Kirchoff by means of an optical spectroscope. It was named for the prominent red lines in its spectrum, from the Latin word rubidus, meaning darkest red. Bunsen prepared free rubidium during the same year by an electrolytic method. After cesium, rubidium is the second most electropositive and alkaline element. The two isotopes of natural rubidium are 85Rb [13982-12-1] (72.15%) and 87Rb [13982-13-3] (27.85%). The latter is a beta-emitter having a half-life of 4.9 x 1010 yr. Twenty-four isotopes of rubidium are known. 

M. le Blanc gave the refractive indices of solii. of potassium and rubidium bromides as 1 5593 and 1 5533 respectively, when the densities are 2"738 and 3 314 respectively. Hence the refraction eq. of potassium bromide by Gladstone and Dale s formula is therefore 24 32 and by Lorentz and Lorenz s formula 14-05 the corresponding values for rubidium bromide are27"62 and 15"98. The mol. refractions of potassium bromide in soln. by the two formulae are respectively 25"11 and 14 70 and of rubidium bromide in soln., 27 85 and 16 33. The mol. refractions of these salts are therefore greater in soln. than in the solid form. Crystals of potassium bromide, says H. Marbuch, exhibit optical activity. A. S. Newcomer found that sodium chloride was the only salt relatively soluble and yet capable of emitting fluorescent rays in the mid-ultra-violet region of the spectrum under the influence of X-rays. 

The existence of these different practices was not sufficient to create a discipline or subdiscipline of physical chemistry, but it showed the way. One definition of physical chemistry is that it is the application of the techniques and theories of physics to the study of chemical reactions, and the study of the interrelations of chemical and physical properties. That would mean that Faraday was a physical chemist when engaged in electrolytic researches. Other chemists devised other essentially physical instruments and applied them to chemical subjects. Robert Bunsen (1811—99) is best known today for the gas burner that bears his name, the Bunsen burner, a standard laboratory instrument. He also devised improved electrical batteries that enabled him to isolate new metals and to add to the list of elements. Bunsen and the physicist Gustav Kirchhoff (1824—87) invented a spectroscope to examine the colors of flames (see Chapter 13). They used it in chemical analysis, to detect minute quantities of elements. With it they discovered the metal cesium by the characteristic two blue lines in its spectrum and rubidium by its two red lines. We have seen how Van t Hoff and Le Bel used optical activity, the rotation of the plane of polarized light (detected by using a polarimeter) to identify optical or stereoisomers. Clearly there was a connection between physical and chemical properties. 

Another experimental proof of the localization of cold atoms at the minima of a periodic optical potential was obtained by recording the resonance fluorescence spectra of cesium atoms trapped in three-dimensional optical molasses (Westbrook et al. 1990) and rubidium atoms in a one-dimensional optical potential (Jessen et al. 1992) The resonance fluorescence spectrum of a motionless two-level atom consists of the well-known Mollow triplet, which includes a central peak at the laser frequency u> and two side components displaced to the red and blue sides by an amount equal to the Rabi frequency (Mollow 1969). For a two-level atom oscillating in a potential well at a frequency lower than the Rabi frequency, each component of the Mollow triplet is split into side components corresponding to changes in the vibrational state of the atom. If the ratio between the oscillation amplitude of the atom in the potential well and the radiation wavelength (the Lamb-Dicke factor) is small, each component of the... 

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See also in sourсe #XX -- [ ]

See also in sourсe #XX -- [ ]

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