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On the Electronic Behavior Retrieved from the Raman Intensity and Resonances in the Highly Excited Molecular Vibration

Author: WangHuanRu
Tutor: WuGuoZuo
School: Tsinghua University
Course: Physics
Keywords: Raman intensity bond polarizabilities electronic structure Raman excited virtual states resonance characteristics
CLC: O561.1
Type: PhD thesis
Year: 2006
Downloads: 281
Quote: 1
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Abstract


Raman spectroscopy has been a powerful tool for the spectroscopic study of molecular structures. Raman intensities include detail information of the interaction between electrons and nuclei. By the emphasis on the Raman intensities, we studied the adsorbed molecules on the metal electrodes. Moreover, the bond polarizability derivatives retrieved from the Raman intensities show some clues to the Raman excited virtual states.Two adsorbate forms of the monothiocyanate complex of chromium ion on the silver electrode are identified by Surface-Enhanced Raman Scattering. By comparing the bond polarizabilities and the force constants, it is obvious that the electronic aspects relating to the bond strength and the Raman intensity are different. Bond polarizability analysis reveals that charge transfer between the adsorbate and Ag adatom/electrode surface is an essential mechanism in SERS.The SERS spectra of the C-H stretching of 2-amino-1-butanol on the Ag and Au electrodes are deconvoluted and analyzed with emphasis on the intensity ratios among the various vibrational modes. The intensity ratios strongly support the proposition of the intramolecular conformational rotation of the molecules absorbed on the Ag (or Au) electrode surface. Both charge transfer and electromagnetic mechanisms play different roles under different voltages.We studied the nonresonant Raman spectroscopy of 2-aminopyridine by 632.8nm and 514.5nm excitations. The contrast between the bond polarizabilities derived from the Raman intensities and the bond electron densities by the quantal calculation reveals the electronic structure of the Raman excited virtual state. Therefore, many ideas can be proposed along this line of reasoning and inference. The theoretical approach to the virtual state also requires further exploration.Highly excited molecular vibration is nonintegrable or even chaotic due to its strong nonlinear resonances among vibrational modes, which leads to serious difficulty by the quantal analysis. By semi-classical method, we studied DCNmolecule with nolinear resonances between D-C and C-N stretches. First, the energy levels were reconstructed by the polyad numbers (approximate quantum numbers) via diabatic correlation. Each polyad number corresponds to a resonance. The idea that a resonance is a mimic of a pendulum hints the nearest level energy spacings of the levels possessing the same polyad number will reach a minimum as they approach the separatrix line in the phase space. This is called Dixon dip. The 1:1 or 2:3 of DCN resonance is eminent in the lower or higher levels, respectively. It’s the operation of these two resonances in the middle levels, which shows chaos. This observation is consistent with Chirikov’s conjecture that resonance overlapping will lead to chaos. The results are also consistent with the analysis by Lyapunov exponent and trajectory plots on the Poincaré’s surface of section.

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CLC: > Mathematical sciences and chemical > Physics > Molecular physics, atomic physics > Molecular Physics > Molecular structure
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