Polyatomic molecules electronic structure

Herzberg contributed to the field of atomic and molecular spectroscopy, where he and his colleagues determined the structures of a large number of diatomic and polyatomic molecules, the structures of free radicals, and the identification of certain molecules in planetary atmospheres, in comets, and in interstellar space. In 1971 he was awarded the Nobel Prize in chemistry for his contributions to the knowledge of electronic structure and geometry of molecules, particularly free radicals. ... 

Herzberg G 1966 Molecular Spectra and Molecular Structure III Electronic Spectra and Electronic Structure of Polyatomic Molecules (New York Van Nostrand-Reinhold)... 

G. Herzberg, Moleculer Spectra and Molecular Structure III. Electronic Spectra of Polyatomic Molecules, Van Nostrand, New York, 1967. 

Another example of reduced symmetry is provided by the changes that occur as H2O fragments into OH and H. The a bonding orbitals (ai and b2) and in-plane lone pair (ai) and the a antibonding (ai and b2) of H2O become a orbitals (see the Figure below) the out-of-plane bi lone pair orbital becomes a" (in Appendix IV of Electronic Spectra and Electronic Structure of Polyatomic Molecules, G. Herzberg, Van Nostrand Reinhold Co., New York, N.Y. (1966) tables are given which allow one to determine how particular... 

The molecular orbital (MO) approach to the electronic structure of diatomic, and also polyatomic, molecules is not the only one which is used but it lends itself to a fairly qualitative description, which we require here. 

As is the case for diatomic molecules, rotational fine structure of electronic spectra of polyatomic molecules is very similar, in principle, to that of their infrared vibrational spectra. For linear, symmetric rotor, spherical rotor and asymmetric rotor molecules the selection mles are the same as those discussed in Sections 6.2.4.1 to 6.2.4.4. The major difference, in practice, is that, as for diatomics, there is likely to be a much larger change of geometry, and therefore of rotational constants, from one electronic state to another than from one vibrational state to another. 

These examples illustrate the principle that atoms in covalently bonded species tend to have noble-gas electronic structures. This generalization is often referred to as the octet rule. Nonmetals, except for hydrogen, achieve a noble-gas structure by sharing in an octet of electrons (eight). Hydrogen atoms, in molecules or polyatomic ions, are surrounded by a duet of electrons (two). 

Each atom in a polyatomic molecule completes its octet (or duplet for hydrogen) by sharing pairs of electrons with its immediate neighbors. Each shared pair counts as one covalent bond and is represented by a line between the two atoms. A Lewis structure does not portray the shape of a polyatomic molecule it simply displays which atoms are bonded together and which atoms have lone pairs. 

J.D. Morgan 111, in Numerical determination of the electronic structure of atoms, diatomic and polyatomic molecules. M. Defranceschi and J. Delhalle Eds., (Kluwer, Dordrecht (1989) p. 49... 

J.G. Fripiat, M. Defranceschi, J. Delhalle in Numerical Determination of the Electronic Structure of Atoms. Diatomic and Polyatomic Molecules. M.Defranceschi, J. Delhalle (eds), NATO-ASI Series C vol. 271, Kluwer Academic Publishers, Dordrecht, 1989, pp. 245-250... 

We can expect that in future it might probably enable us to characterize the reactivity of all reaction participants, including the reaction components and the catalyst itself, in terms of their electronic structure. The quantum chemical methods for approximate description of the polyatomic molecules (reaction components) have already been worked out. However, a very important problem arises here, one which has to be studied carefully, namely, the representation of the catalyst in the frame of this theoretical approach. 

Herzberg, G. Molecular spectra and molecular structure. III. Electronic spectra and electronic structure of polyatomic molecules, Chapt. IV. Princeton, N. J. D. Van Nostrand 1966. 

In this chapter, the diverse coupling constants and MEC components identified in the combined electronic-nuclear approach to equilibrium states in molecules and reactants are explored. The reactivity implications of these derivative descriptors of the interaction between the electronic and geometric aspects of the molecular structure will be commented upon within both the EP and EF perspectives. We begin this analysis with a brief survey of the basic concepts and relations of the generalized compliant description of molecular systems, which simultaneously involves the electronic and nuclear degrees-of-freedom. Illustrative numerical data of these derivative properties for selected polyatomic molecules, taken from the recent computational analysis (Nalewajski et al., 2008), will also be discussed from the point of view of their possible applications as reactivity criteria and interpreted as manifestations of the LeChatelier-Braun principle of thermodynamics (Callen, 1962). 

Mulliken introduced the term "orbital" distinct from "orbital wave function" in 1932 in the second of fourteen papers carrying the general title, "Electronic Structures of Polyatomic Molecules and Valence." Mulliken defined atomic orbitals (AOs) and molecular orbitals (MOs) as something like the... 

Mulliken, Life, 90. On the "orbital," Mulliken wrote in 1932 "From here on, one-electron orbital wave functions will be referred to for brevity as orbitals. The method followed here will be to describe unshared electrons always in terms of atomic orbitals but to use molecular orbitals for shared electrons." In Robert Mulliken, "Electronic Structures of Polyatomic Molecules and Valence," Physical Review 41 (1932) 4971, on 50. 

Electronic Structures of Polyatomic Molecules and Valence." Physical Review 41 (1932) 4971. 

Heberle J (1971) The Debye integrals, the thermal shift and the Mossbauer fraction. In Mossbauer Effect Methodology Vol 7. Gruverman IJ (ed), Plenum, p 299-308 Herzberg G (1945) Molecular Spectra and Molecular Structure. II. Infrared and Raman Spectra of Polyatomic Molecules. Von Nostrand Reinhold, New York Hohenberg P, Kohn W (1964) Inhomogeneous electron gas. Phys Rev 136 B864-871... 

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