Molecular shape triatomic molecule

The extension of molecular orbital theory to triatomic molecules is a major part of this chapter. It gives a very satisfactory description of the shapes and the bonding of molecules in general, and is consistent with observations of photoelectron and electronic absorption spectra. It is not possible for the VSEPR theory to explain these latter observations. 

The idea that distortion of a triatomic molecule from a linear to a bent shape occurs if the HOMO and LUMO are of the same symmetry representation, so that electrons in the HOMO are stabilized, was discussed as a tentative general approach to molecular shape. 

The density functional method as applied by Tarazona to deal with classical fluids has been used to calculate the orientation of triatomic molecular fluids near the solid-liquid interface. The results give valuable suggestions about the effect of molecular shape on the orientation of real molecules such as liquid crystals near the solid-fluid interface. 

Accordingly, given the above guidelines, suggest the shape that will be adopted by a triatomic molecule of general formula AB2 that only has electrons in the two molecular orbitals required to... 

This approach was first applied to relatively simple cases many years ago by Walsh4 and led to certain generalizations, called Walsh s rules, relating the shapes of triatomic molecules to their electronic structures. The basic approach is to calculate, or estimate, the energies of molecular orbitals for two limiting structures, say, Unear and bent (to 90°) for an AB2 molecule,... 

The passage from diatomic to triatomic molecules leads to the doublesided world of linear and bent molecular shapes. Although strictly correlated, the respective rovibrational spectra require distinct treat-... 

Can Lewis structures provide us with information regarding the actual spatial arrangements of atoms within molecules To explore this question, let us invent a triatomic molecule and call it XY2, in which X is the central atom with bonds to each Y atom. Each bond is polar since the joined atoms have different electronegativities. Therefore each bond contributes to the overall dipole moment of the molecule. Consider two possibilities for the molecular shape, linear and bent ... 

Because the central atom is not in line with the other two, the symmetric stretching vibration produces a change in dipole moment and is thus IR active. For example, stretching peaks at 3657 and 3766 cm (2.74 and 2.66 pm) appear in the IR spectrum for the symmetric and asymmetric stretching vibrations of the water molecule. There is only one component to the scissoring vibration for this nonlinear molecule Irecause motion in the plane of the molecule constitutes a rotational degree of freedom. For water, the bending vibration causes absorption at 1595 cm (6 27 pm). The difference in behavior of linear and nonlinear triatomic molecules with two and three absorption bands, respectively, illustrates how IR absorption spectroscopy can sometimes be used to deduce molecular shapes. 

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