tailieunhanh - Ideas of Quantum Chemistry P11

Ideas of Quantum Chemistry P11 shows how quantum mechanics is applied to chemistry to give it a theoretical foundation. The structure of the book (a TREE-form) emphasizes the logical relationships between various topics, facts and methods. It shows the reader which parts of the text are needed for understanding specific aspects of the subject matter. Interspersed throughout the text are short biographies of key scientists and their contributions to the development of the field. | 66 2. The Schrödinger Equation Is therefore the very meaning of the dipole moment a quantity often used in chemistry and physics a fairy tale If HCl has no dipole moment then it is more understandable that H2 does not have either. All this seems absurd. What about this dipole moment Let us stress that our conclusion pertains to the total wave function which has to reflect the space isotropy leading to the zero dipole moment because all orientations in space are equally probable. If one applied the transformation r -r only to some particles in the molecule . electrons and not to others . the nuclei the wave function will show no parity it would be neither symmetric nor antisymmetric . We will introduce the Hamiltonian in Chapter 6 which corresponds to immobilizing the nuclei clamped nuclei approximation in certain positions in space and in such a case the wave function depends on the electronic coordinates only. This wave function may be neither symmetric nor antisymmetric with respect to the partial inversion transformation r -r for the electrons only . To give an example let us imagine the HF molecule in a coordinate system its origin in the middle between the H and F nuclei. Consider a particular configuration of the 10 electrons of the molecule all close to the fluorine nucleus in some well defined points. One may compute the value of the wave function for this configuration of electrons. Its square gives us the probability density of finding this particular configuration of electrons. Now imagine the partial inversion r -r applied to all the electrons. Now they will all be close to the proton. If one computes the probability density for the new situation one would obtain a different value much much smaller because the electrons prefer the fluorine not the hydrogen . No symmetry or antisymmetry. No wonder therefore that if one computed p t 0N jlaI 0 v with such a function integration is over the electronic coordinates only the result would differ from .