I atom

Figure B2.5.12 shows the energy-level scheme of the fine structure and hyperfme structure levels of iodine. The corresponding absorption spectrum shows six sharp hyperfme structure transitions. The experimental resolution is sufficient to detennine the Doppler line shape associated with the velocity distribution of the I atoms produced in the reaction. In this way, one can detennine either the temperature in an oven—as shown in Figure B2.5.12 —or the primary translational energy distribution of I atoms produced in photolysis, equation B2.5.35.

B2.5.351 after multiphoton excitation via the CF stretching vibration at 1070 cm. More than 17 photons are needed to break the C-I bond, a typical value in IR laser chemistry. Contributions from direct absorption (i) are insignificant, so that the process almost exclusively follows the quasi-resonant mechanism (iii), which can be treated by generalized first-order kinetics. As an example, figure B2.5.15 illustrates the fonnation of I atoms (upper trace) during excitation with the pulse sequence of a mode-coupled CO2 laser (lower trace). In addition to the mtensity, /, the fluence, F, of radiation is a very important parameter in IR laser chemistry (and more generally in nuiltiphoton excitation) ... 

The classical-mechanical problem for the vibrational motion may now be solved using Newton s second law. The force on the x component of the i atom is... 

Iodine [7553-56-2] I, atomic number 53, atomic weight 126.9044, is a nonmetaUic element belonging to the halogen family in Group 17 (VIIA) of the Periodic Table. The only stable isotope has a mass number of 127. There are 22 other iodine isotopes having masses between 117 and 139 14 of these isotopes yield significant radiation. 

An unusual crystal arrangement is exhibited by the isomorphous compounds CrCl and Crl. The close-packed cubic array of Cl or I atoms has two-thirds of the octahedral holes between every other pair of chlorine or iodine planes filled with chromium atoms. Alternate layers of the halogen compounds are held together by van der Waals forces (39,40). 

Figure 7.10 Structure of yellow Til (a) showing its relation to NaCI (b). Tl has 5 nearest-neighbour I atoms at 5 of the vertices of an octahedron and then 21 + 2T1 as next-nearest neighbours there is one I at 336 pm. 4 at 349 pm, and 2 at 387 pm, and the 2 close Tl -Tl approaches, one at 383 pm. InX (X = Cl, Br, I) have similar structures in their red forms.

Unlike its analogue FCIO3 it forms adducts with BF3 and AsFs, possibly by F" donation to give [I03]+[BF4 ] and [I03]+[AsF6]", though the structures have not yet been determined. Alternatively, the coordination number of the central I atom might be increased. SO3 reduces FIO3 to iodyl fluorosulfate ... 

As an illustration, in the iodine monochloride (I — Cl) molecule, the electron pair being shared remains closer to the more electronegative Cl atom. This creates fractional negative and positive charges, referred to as formal charges, on the Cl and I atoms, respectively, as illustrated below ... 

Polar molecules, like nonpolar molecules, are attracted to one another by dispersion forces. In addition, they experience dipole forces as illustrated in Figure 9.9, which shows the orientation of polar molecules, such as Id, in a crystal. Adjacent molecules line up so that the negative pole of one molecule (small Q atom) is as dose as possible to the positive pole (large I atom) of its neighbor. Under these conditions, there is an electrical attractive force, referred to as a dipole force, between adjacent polar molecules. 

The gold(I) atoms have linear coordination (Figure 4.3) and the gold(III) atoms square planar coordination [24]. 

A more general development of this treatment was provided by Allnatt and Jacobs [429], The differential equation which expresses the number of germ nuclei, Nt, which have received i atoms is... 

One form of the polyatomic ion I, has an unusual V-shaped structure one I atom lies at the point of the V, with a linear chain of two I atoms extending on each side. The bond angles are 88° at the central atom and 180° at the two atoms in the side chains. Draw a Lewis structure for L that explains its shape and indicate the hybridization you would assign to each nonterminal atom. 

---