Cesium atom

In more recent experiments using a cesium atomic beam, temperatures as low as 2.5 pK have been reported.1111 Enthusiastic workers in the field predict that the temperature may be decreased by as much as another factor of 106 before the final minimum temperature is realized, and perhaps temperatures lower than 2.5 pK have been claimed by now.bb... 

In the technique developed by Willard Libby in Chicago in the late 1940s, the proportion of carbon-14 in a sample is determined by monitoring the (1 radiation from C02 obtained by burning the sample. This procedure is illustrated in Example 17.4. In the modern version of the technique, which requires only a few milligrams of sample, the carbon atoms are converted into C ions by bombardment of the sample with cesium atoms. The C ions are then accelerated with electric fields, and the carbon isotopes are separated and counted with a mass spectrometer (Fig. 17.19). 

C. A., Van Dorn, L.O. and Wilkinson, C.C. (2002) Most easily-ionized, closed-shell molecules known easier than the cesium atom. Science, 298, 1971-1974 ... 

Two of the three SI base units have in the meantime acquired redefinitions in atomic terms (e.g., the second is now defined as 9 192 631 770 hyperfine oscillations of a cesium atom). However, the definitions (C.2a)-(C.2c) conceal another unfortunate aspect of SI units that cannot be overcome merely by atomic redefinitions. In the theory of classical or quantal electrical interactions, the most fundamental equation is Coulomb s law, which expresses the potential energy V of two charged particles of charge q and 2 at separation R as... 

The four quantum numbers (n, l, mh and ms) that describe the valence electron in the cesium atom are... 

The valence electron for the cesium atom is in the 6s orbital. In assigning quantum numbers, n = principal energy level = 6. The quantum number l represents the angular momentum (type of orbital) with s orbitals = 0, p orbitals = 1, d orbitals = 2, and so forth. In this case, l = 0. The quantum number m is known as the magnetic quantum number and describes the orientation of the orbital in space. For, v orbitals (as in this case), mt always equals 0. For p orbitals, mt can take on the values of -1, 0, and +1. For d orbitals, can take on the values -2, -1, 0, +1, and +2. The quantum number ms is known as the electron spin quantum number and can take only two values, +1/2 and -1/2, depending on the spin of the electron. 

Cesium (atomic radius = 0.255 nm) crystallizes with a body-centered cubic unit cell. What is the approximate length of a side of the cell (/3=1.73)... 

Gomplexation of cesium at a tetracarbaborane cage was achieved in the reaction of [ / >-2,4,6,12-(SiMe3)4-2,4,6,12-C4B8H8] with an excess quantity of cesium metal in THF. In the polymeric structure of the cesium salt, one cesium atom occupies an apical position above an open six-membered C3B3 face 5.19... 

This vapor pressure can be deduced from kinetic theory and the rate of arrival of Cs atoms per square centimeter per second (3,4). This arrival rate. A, can be calculated from the measured value of the saturation positive ion current. Langmuir first showed that if the tungsten is hot enough every cesium atom that strikes the surface evaporates off as a positive ion of cesium. This saturated positive ion current, i.p, can be measured easily with a medium sensitive galvanometer when the collector is negative. It is related to A by the equation... 

Suppose the vapor pressure is adjusted so that the arrival rate. A, is about 2.6 X 10 cesium atoms/cm.Vsec. If the temperature of the tungsten filament is about 550°K., the surface will be covered with more... 

Fig. 5. Cesium atom evaporation rate versus amount of adsorbed cesium.

In this section certain conclusions will be drawn regarding the nature of the adsorbed cesium particles and the effects that these particles have on the electron emission and on other adsorbed particles. From the fact that both atoms and ions of cesium evaporate from the surface at the same time, we conclude that both atoms and ions exist on the surface. This conclusion is based on the probable assumption that as the cesium atom approaches the clean surface, the forces which tend to remove the valence electron from the cesium atom become increasingly larger the nearer the atom is to the surface. That these forces are comparable with the forces that tend to keep the electron associated with its nucleus follows from the fact that for clean tungsten is about 4.6 volts and the ionization potential for cesium is 3.9 volts. That both adatoms and adions... 

Fig. 11. Potential energy versus distance for a cesium atom (upper curve) and for an ion (lower curve) near a tungsten surface.

In Figure 9 note also that constant with 8. This means that the fields produced by neighboring ions is not strong enough to polarize an adatom appreciably and thus to change its escape probability. The value of [Pg.155]

When it reaches its distance of closest approach" to the tungsten atoms, strong repulsive forces are exerted between the electrons in the cesium atom and the electrons in the tungsten atoms and the energy of the system rises extremely rapidly. 

According to Lennard-Jones (6), the attractive energy varies as the inverse sixth power of the distance while the repulsive energy varies approximately as the inverse twelfth power. The radius of a cesium atom is about 2.7A., and it can sink about O.sA.. below the surface. Hence its nucleus will be 2.2A. above the surface. According to Figure 9, (Pa = 2.4 volts. This locates the minimum in the atom curve in Figure 11. 

Before proceeding with the next topic, we should like to emphasize again the significance of this work on the problem of understanding catalysis. The conversion of a cesium atom to a cesium ion is the simplest illustration of a catalytic reaction since it involves the transfer of an electron. To convert about 10% of the cesium atoms in free space into cesium ions would require a temperature of 20,000°K. This can be calculated from the equations... 

Since the heat of evaporation of cesium atoms from the second atom layer is 17,500 cal., according to Taylor and Langmuir (54), and since evaporation occurs from the half crystal position c we find... 

Because of the high value of pc the cesium atoms will remain in the position c for most of the time. Since the 011 planes on the tungsten wires used by Taylor and Langmuir might have had several steps, diffusion may not have occurred on the planes themselves but along the... 

Fig. 5-7.—The structure of the tetragonal crystals CstAgAuCle and Cs2AuAuCU. Large full circles represent cesium atoms, large open circles chlorine atoms, and small circles gold or silver atoms.

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