Raman intensity computation of small molecules, helical molecules, and DNA
Abstract
In Chapter II, an Anharmonic Potential-Effective Charge approach for computing relative Raman intensities of a gas is developed. The equations of motion are set up and solved for the driven anharmonic molecular vibrations. An explicit expression for the differential polarizability tensor is derived and its properties discussed. This expression is then used within the context of Placzek's theory to compute the Raman cross section and depolarization ratio of a gas. The computation is carried out for the small molecules: $CO\sb2$, $CS\sb2$, $SO\sb2$ and $CCl\sb4$; results are compared with experimental measurements and discussed. In Chapter III, a general expression of cubic force constants of a helical molecule is derived and its properties discussed. Explicit expressions are listed for the cases of stretch and anglebend contributions. Some uses of anharmonic force constants, as in Raman scattering computations, are also discussed. In Chapter IV, an Anharmonic Potential-Effective Charge approach is employed to treat Raman scattering from a helical molecule. Equations of motion are set up and solved. General expressions of dipole moments for various incident and scattered polarizations are derived. Raman selection rules are deduced therefrom and shown to form a set including, but larger than, the set derived by Higgs. Far from resonance, expressions of dipole moments are obtained and selection rules are shown to reduce to the Higgs ones. Symmetry of differential polarizability tensor is examined far from resonance and also under the additional assumption of weak coupling. Finally, in Chapter V, the approach of Chapter IV is applied to DNA, and the results of the computations are reported.
Degree
Ph.D.
Advisors
Zandt, Purdue University.
Subject Area
Molecules
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