Resonant periodic orbits molecules

Marston, C.C. and Wyatt, R.E. (1984a). Resonant quasi-periodic and periodic orbits for the three-dimensional reaction of fluorine atoms with hydrogen molecules, in Resonances in Electron-Molecule Scattering, van der Waals Molecules, and Reactive Chemical Dynamics, ed. D.G. Truhlar (American Chemical Society, Washington, D.C.). 

ABSTRACT. The mechanisms for energy flow from overtone excited HC and HO local modes have been elucidated in two mode model Hamiltonians of benzene and trihalomethanes and in a six mode model of HOOH molecule. Intramolecular vibrational relaxation (IVR) from the excited 2 1 Fermi resonance is shown to be very sensitive to the stretch-bend potential energy coupling in connection with the stability of the HC stretch periodic orbit. The overtone induced dissociation of HOOH, which is a slow process in comparison with the initial HO overtone relaxation, is explained in terms of the details of the potential energy surface. 

It is difficult to give a localized orbital description of the bonding in a period 3 hypervalent molecule that is based only on the central atom 3s and 3p orbitals and the ligand orbitals, that is, a description that is consistent with the octet rule. One attempt to do this postulated a new type of bond called a three-center, four-electron (3c,4e) bond. We discuss this type of bond in Box 9.2, where we show that it is not a particularly useful concept. Pauling introduced another way to describe the bonding in these molecules, namely, in terms of resonance structures such as 3 and 4 in which there are only four covalent bonds. The implication of this description is that since there are only four cova-... 

In the Landauer/Imry limit, the transport through the junction is due to elastic scattering. If the gap between the injection energy and the frontier orbital resonance is large, the Landauer/Buttiker contact time is very small, so that the charge is present on the molecule for a very short time. This means that its interaction with any vibration will be weak, because there just is not time to complete a full vibrational period before the charge has gone into the electrode sink. 

IN the past twenty years the electronic structures of many organic molecules, particularly benzene and related compounds, have been discussed in toms of the molecular orbital and valence bond methods.1 During the same period the structures of inorganic ions have been inferred from the bond distances f a bond distance shorter than the sum of the conventional radii has been attributed to the resonance of double bonded structures with the single bonded or Lewis structure. 

In this chapter we have explored the structure of organic compounds. This is important since structure determines reactivity. We have seen that weak bonds are a source of reactivity. Strong bonds are made by good overlap of similar-sized orbitals (same row on periodic table). Bends or twists that decrease orbital overlap weaken bonds. Lewis structures and resonance forms along with electron flow arrows allow us to keep track of electrons and explain the changes that occur in reactions. VSEPR will help us predict the shape of molecules. Next we must review how bonds are made and broken, and what makes reactions favorable. Critical concepts and skills from this chapter are ... 

A stepwise process is used to convert a molecular formula into a Lewis structure, a two-dimensional representation of a molecule (or ion) that shows the relative placement of atoms and distribution of valence electrons among bonding and lone pairs. When two or more Lewis structures can be drawn for the same relative placement of atoms, the actual structure is a hybrid of those resonance forms. Formal charges are often useful for determining the most important contributor to the hybrid. Electron-deficient molecules (central Be or B) and odd-electron species (free radicals) have less than an octet around the central atom but often attain an octet in reactions. In a molecule (or ion) with a central atom from Period 3 or higher, the atom can hold more than eight electrons by using d orbitals to expand its valence shell. 

---