Keesom

Table VI-1 shows the approximate values for the Keesom Debye,...

Attractive and Repulsive Forces. The force that causes small particles to stick together after colliding is van der Waals attraction. There are three van der Waals forces (/) Keesom-van der Waals, due to dipole—dipole interactions that have higher probabiUty of attractive orientations than nonattractive (2) Debye-van der Waals, due to dipole-induced dipole interactions (ie, uneven charge distribution is induced in a nonpolar material) and (J) London dispersion forces, which occur between two nonpolar substances. 

LW) interactions refer to the purely physical London s (dispersion), the Keesom s (polar) and Debye s (induced polar) interactions and correspond to magnitudes ranging from approximately 0.1 to 10 kJ/mol (but in rare cases may be higher). The polar forces in the bulk of condensed phases are believed to be small due to the self-cancellation occurring in the Boltzmann-averaging of the multi-body... 

There are three types of interactions that contribute to van der Waals forces. These are interactions between freely rotating permanent dipoles (Keesom interactions), dipole-induced dipole interaction (Debye interactions), and instantaneous dip le-induced dipole (London dispersion interactions), with the total van der Waals force arising from the sum. The total van der Waals interaction between materials arise from the sum of all three of these contributions. 

The dipole-dipole (Keesom) interaetion eomes about from the faet that on the average, two freely rotating dipoles will align themselves so as to result in an attraetive foree, similar to that eommonly observed with bar magnets. In order to ealeulate the net dipole-dipole interaetion, it is neeessary to examine all the possible orientations of the dipoles with respeet to one another. It is also neeessary to determine any jr effeets due to the field assoeiated with a point eharge, in order to determine the net effeet when amorphous solids are plaeed side by side. We also need to eonsider what happens if the dipoles ean reorient in eaeh other s fields. 

It should be noted that, if the medium between the particle and substrate is something other than vacuum and possesses a dielectric constant e, the interaction energy in Eq. 68 is reduced by a factor of Eq. 68, which relates the interaction energy between permanent electric dipoles and their separation distances is known as the Keesom effect. 

The total van der Waals interaction potential is obtained by simply adding the individual contributions arising from the Keesom, Debye, and London interactions. Because the radial power-law dependencies of all these interactions vary as 1 /r, the total van der Waals interaction can be expressed simply as... 

The relative contributions to van der Waals interactions arising from the Debye, Keesom, and London effects... 

It is clear from Table 1 that, for a few highly polar molecules such as water, the Keesom effect (i.e. freely rotating permanent dipoles) dominates over either the Debye or London effects. However, even for ammonia, dispersion forces account for almost 57% of the van der Waals interactions, compared to approximately 34% arising from dipole-dipole interactions. The contribution arising from dispersion forces increases to over 86% for hydrogen chloride and rapidly goes to over 90% as the polarity of the molecules decrease. Debye forces generally make up less than about 10% of the total van der Waals interaction. 

It should also be noted that contributions to van der Waals interactions from the Keesom effect are likely to be decreased in solids due to the locking in of the... 

It has been known since the beginning of recorded history that not all liquids are completely miscible with one another. But only in recent times have we learned that gases may also, under suitable conditions, exhibit limited miscibility. The possible existence of two gaseous phases at equilibrium was predicted on theoretical grounds by van der Waals as early as 1894, and again by Onnes and Keesom in 1907 (see R8). Experimental verification, however, was not obtained until about forty years later, primarily by Krich-evsky, Tsiklis, and their co-workers in Russia (see Gl, SI), by Lindroos and Dodge at Yale (L5), and, more recently, by de Swaan Arons and Diepen at Delft (D3). 

Keesom (1879-1956) used the polarity of molecules to explain the viseosity of substanees. 

Dipole-dipole forces, the so-called Keesom forces 8ind8o> appear when both the solvent and solute have dipole moments. Strong interactions are produced as a result of dipole alignment. Dipole interactions are determined by the sum of all the dipoles within a molecule. 

Saul Oseroff and Pieter H. Keesom, Magnetic Properties Macroscopic Studies T. Giebultowicz and T.M. Holden, Neutron Scattering Studies of the Magnetic Structure and Dynamics of Diluted Magnetic Semiconductors J. Kossul, Band Structure and Quantum Transport Phenomena in Narrow-Gap Diluted Magnetic Semiconductors... 

Abbreviations are in parentheses. The dd interactions are also known as Keesom interactions di interactions are also known as Debye interactions ii interactions are also known as London or dispersion interactions. Collectively, dd, di and ii interactions are known as van der Waals interactions. Charge transfer interactions are also known as donor-acceptor interactions. 

Dipole-induced dipole forces. A molecule with a strong molecular or bond dipole can induce a dipole in a molecule nearby that is polarizable. These Keesom forces have the same inverse 6th power dependence with distance. An example could be the interaction of chlorobenzene with naphthalene. 

Keesom, W. H. and van Dijr, H. On the possibility of separating neon and its isotopic components by rectification. Koninklijke Akademie van Wetenschappen te Amsterdam, Proc. of the Sect, of Sciences XXXIV, 42-50 (1931) Keesom, W. H. and Hantjes, Vapor pressures of neon of different isotopic compositions. J. Physica 2, 986-999 (1935). 

Keesom relationship phys chem An equation for the potential energy associated with the interaction of the dipole moments of two polar molecules. ka-sam ri la-sh3n,ship ... 

In order to have localized adsorption with only physical interaction it is clear that either the interaction must be strong, or the kinetic energy of the adsorbed molecules must be small. As an example of the latter condition we have the work of Keesom and Schweers (24, 25) for low temperature adsorption of hydrogen and neon on glass. They assumed that the actual area of the glass was equal to the apparent area, and the results in Table IX were worked out for = 3 on that basis. The... 

The dipole-dipole interactions, frequently referred to as Keesom interactions, are historically included in the van der Waals interactions, even though they are purely electrostatic. For molecules that are free to orient themselves, the dipole-dipole interactions must be averaged over the molecular orientations, as the angular dependence of the interaction energy is comparable to the Boltzmann energy kBT (Israelachvili 1992, p. 62). With the averaging of the Keesom... 

S. Oseroff and P. H. Keesom, Magnetic Properties Macroscopic Studies... 

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