IVR Viewed Through State‐Selected Dispersed Fluorescence Spectroscopy of Jet‐Cooled Polyatomics

Abstract

State selected dispersed fluorescence spectroscopy provides a means of unscrambling the identity of emitting states in polyatomic manifolds that are extensively mixed relative to the basis set pertinent to lower parts of the manifold. A view is presented of the methodology that may be used to unravel complex electronic spectra when information from dispersed fluorescence is available. The dispersed fluorescence spectrum serves as a means of projecting the excited state electronic wave function onto the ground state potential surface, thereby allowing the vibrational composition of the (mixed) excited state eigenvector to be evaluated in terms of a ground state vibrational basis. Examples are drawn from experimental data relating to the spectroscopy of benzene and azulene. In the case of benzene‐d6, Fermi resonances between the levels comprising the progressions 61 1n and 61 1021n‐1 lead to an interesting pedagogical example of how dispersed fluorescence spectroscopy may be used to chart IVR as it progresses from isolated mixing of a few states to more widespread scrambling of vibrational identity among many states. Azulene serves as an example of the more extreme case of widespread state mixing that in large polyatomics has its onset in relatively low regions of the excited state vibrational manifold. It is demonstrated that vibrational state mixing in azulene is still amenable to a detailed analysis that yields the composition of mixed eigenvectors.

Unimolecular Dissociation of C6H6–C6Cl6 Complex and Effect of Mode–Mode Coupling

“…IVR plays an important role in determining the rate of unimolecular reactions . The importance of IVR has been described in many studies in the literature. − Dynamical instabilities of molecules may also appear due to nonlinear resonances in their vibrational modes. The studies of nonlinear resonances in mode–mode energy-transfer dynamics were explored in the past. − In the study of photoisomerization dynamics of stilbenes, the large amplitude torsion motion of the phenyl rings was found important as it is the primary component of the reaction coordinate .…”