Perturbations of vibrational and rotational spectra in polyatomic molecules
Abstract
The analysis of perturbed structure usually reveals very important dynamical and structural information, and the accumulation of such knowledge over the years has contributed greatly to our understanding of chemical reactions. Study of perturbations in polyatomic molecules is a logical extension from diatomic molecules although problems are in general more challenging due to more complex perturbation patterns. Complex classes of perturbations can be isolated and understood by choosing specific chemical systems that give us some control of the perturbation to be observed. Then we can study one specific perturbation or study the coupling of perturbations. In this thesis, perturbations of electronic states, including Jahn-Teller coupling or spin-orbital coupling, are studied in propyne ion by delayed pulsed-field ionization zero-kinetic-energy (ZEKE) photoelectron spectroscopy. Perturbations between vibronic states including Fermi resonance and Coriolis coupling are examined in the 3p$\sigma$ Rydberg state and the cation of NO$\sb2$ probed by (2+1) resonant multiphoton ionization spectroscopy (REMPI) and ZEKE photoelectron spectroscopy. This comparison indicates that core-electron coupling in the NO$\sb2$ 3p$\sigma$ Rydberg state does not affect the anharmonic mixing of vibrational states. Autoionization, which occurs when a bound, discrete rotation-vibration level couples with a continuum state, has been probed by REMPI spectra of NO$\sb2\sp+$. The core-electron dynamics are found to be totally altered when an autoionizing state couples with the other vibrational state via Fermi resonance. More detailed information about autoionization intensities and selection rules is obtained for the same system probed by three-color, triple-resonant ZEKE spectroscopy. Off-diagonal transitions observed in the ZEKE spectra by adding the third color, $\omega\sb3$, from 3p$\sigma$ (000) to ionic ($\nu\sb1$, $\nu\sb2$, $\nu\sb3$) are compared with the evaluation of the transition matrix element based on Henberg-Teller theory, including intensity borrowing due to autoionization.
Degree
Ph.D.
Advisors
Grant, Purdue University.
Subject Area
Chemistry
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