Mode-selected dynamics and vibronic interactions in the high Rydberg states of nitrogen dioxide

Francis Xavier Campos, Purdue University

Abstract

Spectra of the autoionizing Rydberg states of NO$\sb2$ are interpreted qualitatively, noting particularly the similarities to features observed in the spectra of diatomic molecules. Rotationally resolved spectra were obtained by multiresonant ionization spectroscopy in a supersonic expansion using low lying valence states and the 3p$\sigma\ \sp{2}\Sigma\sb{\rm u}\sp+$ state as intermediates. The spectra evidence electronic structure well described by the Rydberg model. Vibronic coupling and decay rates dependent on the vibrational mode strongly influence the intensity, width and shape of the resonances. The spectra obtained in the (100) manifold reveal s$\sigma$, d$\sigma$ and d$\pi$ Rydberg series with principal quantum numbers ranging from 9 to 50. The states decay almost entirely by autoionization and the resonance widths imply widely varying decay rates depending on the principal quantum number and electron angular momentum. The complete transition from Hund's case b to d is also documented. A series of strong perturbations causing intensity losses and energy shifts is assigned to vibronic interactions with the (110) p$\sigma$ and p$\pi$ states. Very different decay dynamics are observed in the (010) manifold. These states are longer lived than (100) states and neutral dissociation is an important decay mechanism. Comparison with the spectra from the (100) and (110) manifolds shows that autoionization by $\nu\sb1$ is much faster than autoionization by $\nu\sb2$ and that $\nu\sb2$ seems to promote dissociation. Spectra from the (200) and (300) states show broad resonances for states requiring autoionization via $\Delta$v $<\ -$1 processes. Vibronic coupling with lower vibrational states is strong and two complex resonances are identified. The extensive mixing of vibrational character throughout the spectrum promotes multiquantum autoionization. The dependence of efficient autoionization on vibronic coupling to other manifolds also explains the existence of some weak resonances.

Degree

Ph.D.

Advisors

Grant, Purdue University.

Subject Area

Chemistry

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