tailieunhanh - Ideas of Quantum Chemistry P71

Ideas of Quantum Chemistry P71 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. | 666 12. The Molecule in an Electric or Magnetic Field where the shielding constant ac characterizes the vicinity of the nucleus. For the isolated nucleus ac 0. Example 4. The methane molecule 13CH4 in magnetic fieldH This time there is an additional magnetic field coming from four equivalent protons each having IH 2. The energy levels of the carbon magnetic spin result from the magnetic field and from the mI H s of the protons according to eq. Fig. . The resonance of the 13C nucleus means a transition between energy levels that correspond to mI C 2 with all the mIyHi being Thus the lower level corresponds to E mpH1 mI H2 mItH3 mpH4 -xH 1 - ac yc x JcHÎmjH mpH2 m H3 mpH4 2 2 1 2 3 4 and at the higher level we have the energy E- m Hi mI Hl imI H3 mI H4 2H 1 - c Yc - 2 JCH mI H1 mI H2 mI H3 mI H4 Since mIyHi 2 then each of the levels E will be split into 5 levels Fig. a non-degenerate level arising from all mIyHi 2 a quadruply degenerate level that comes from all mItHi 2 except one equal to -1 there are four positions of this one a sextuply degenerate level that results from two mIyHi 2 and two mIyHi -2 six ways of achieving this a quadruply degenerate level that comes from all mIyHi - 2 except one that equals 2 there are four positions of this one a non-degenerate level arising from all mIyHi - 2 THE RAMSEY THEORY OF THE NMR CHEMICAL SHIFT An external magnetic field H or and the magnetic field produced by the nuclei magnetic dipole moments Mi M2 M3 . certainly represent an extremely weak perturbation to the energy of a molecule and therefore the changes they induce in the molecule are suitable for perturbational methods. We decide to apply the theory through the second order. Such an effect is composed of two parts the first-order correction the diamagnetic contribution the second-order correction theparamagnetic contribution . 73The NMR selection rule for a given nucleus says that the single nucleus undergoes a flip. The .

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