Fluorescence Excitation Spectroscopy of the 3p Rydberg States of 1-Azabicyclo[2.2.2]octane and 1-Azaadamantane

Abstract

The singlet states of the 3p Rydberg manifold of the structurally rigid amines 1-azabicyclo[2.2.2]octane and 1-azaadamantane seeded in supersonic expansions have been investigated by means of fluorescence excitation spectroscopy. Under these conditions a better spectral resolution could be obtained than in previous studies, enabling us to resolve and identify unambiguously the transitions to the second and third excited singlet states. These states are assigned as the 11E and 31A1 states, associated with excitation of a lone-pair electron to the 3px,y and 3pz Rydberg orbitals, respectively. Analysis of the vibrational energies and intensities of vibronic transitions observed in the excitation spectra of both states leads to the conclusion that the equilibrium geometry and vibrational properties of the molecule in these two states resemble closely those of the lowest excited singlet state, which derives from excitation of a lone-pair electron to the 3s Rydberg orbital, and those of their ionic core. Excitation spectra in combination with dispersed emission spectra and fluorescence decays demonstrate that internal conversion to the lowest excited singlet state shows up prominently in the dynamics of the 3p Rydberg states.