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Dipole moment, inter-atomic

Table 4.5. Cartesian dipole components of the H2-He system, for three inter-nuclear spacings r after [279]. The center-of-mass of the H2 molecule is at the origin and the He atom is at z = R. A positive induced dipole moment p2 corresponds to the polarity H He+ (py — 0). Table 4.5. Cartesian dipole components of the H2-He system, for three inter-nuclear spacings r after [279]. The center-of-mass of the H2 molecule is at the origin and the He atom is at z = R. A positive induced dipole moment p2 corresponds to the polarity H He+ (py — 0).
Even in atoms and molecules possessing no permanent dipole moment, the continuous electronic movement results, at any instant, in a small dipole moment fi, which can fluctuatingly polarize the electron system of the neighbouring atoms or molecules. This coupling causes the electronic movements to be synchronized in such a way that a mutual attraction results. The energy of such so-called dispersion or London [33] inter-... [Pg.13]

For the four chnical anesthetics, d i,(z) exhibits minima at the interface. Thus, all these molecules are inter-facially active. However, the degree to which they tend to accumulate at the interface differs. For cyclopropane and nitrous oxide, the depths of the interfacial minima in measured with respect to the free energy in hexane, is smaller than 1 kcal/mol. The minima for isoflurane and desflurane are considerably deeper, approximately 2-2.5 kcal/mol. The interfacial activity of the solutes can be related to their polarity. Isoflurane and desflurane have an average permanent dipole moment of approximately 2 D. In contrast, cyclopropane is a symmetrical molecule with no permanent dipole moment, and the dipole moment of nitrous oxide is only 0.2 D. In spite of their small dipole moments, however, these molecules should be considered as weakly polar rather than non-polar. They are involved in non-negligible electrostatic interactions with water, that are primarily due to higher molecular multipole moments arising from substantial partial charges on the atoms. [Pg.41]

Fig. 4 Geometry of chlorophyll interactions for dipolar approximation, (a) Porphyrin ring of a chlorophyll molecule. The transition dipole moment for the Qy state is approximately along a vector connecting the and N/) atoms, (b) Inter-chlorophyll coupling between two chlorophylls in the dipolar approximation is determined by their transition dipole moments d/ and the vector r,j connecting their central Mg atoms, see Eq. (3). Fig. 4 Geometry of chlorophyll interactions for dipolar approximation, (a) Porphyrin ring of a chlorophyll molecule. The transition dipole moment for the Qy state is approximately along a vector connecting the and N/) atoms, (b) Inter-chlorophyll coupling between two chlorophylls in the dipolar approximation is determined by their transition dipole moments d/ and the vector r,j connecting their central Mg atoms, see Eq. (3).
The discovery and identification of buckminsterfullerene, Cgo [121], was one of the most talked-about developments in chemistry in the latter part of the twentieth century, although it has been eclipsed in applications by carbon nanotubes and, more recently, graphene. The discovery was largely fortuitous, as the experiments were intended to shed light on the formation of long chains of carbon atoms, which account for much of the carbon observed in inter-stellar space. It eventually resulted in the award of a Nobel Prize to microwave spectroscopists - for a molecule without a dipole moment Identifying chemical species in space is normally done by observation of their rotational spectra (Section 7.5.1), so confirmation of the existence of fullerenes in inter-stellar dust clouds took a long time, eventually achieved by observation of four infrared frequencies characteristic of Ceo, as well as several that correspond to C70 [122],... [Pg.459]

Van der Waals force Also called intermolecular forces, secondary valence forces, dispersion force, London dispersion force, or van der Waals attraction. It is an attractive force between two atoms or non-polar molecules, which arise because a fluctuating dipole moment in one molecule induces a dipole moment in the other, and the two dipole moments then interact. They are somewhat weaker than hydrogen bonds and far weaker than inter-atomic valences. Information regarding their numerical values is mostly semi-empirical, derived with the aid of theory from an analysis of physical and chemical data. [Pg.543]


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