Analysis of the torsional potential of 9,10‐dihydrophenanthrene in three electronic states: S, S₁, and cation ground state Available to Purchase

Vibronic spectra are measured for the ground, first excited, and ion ground state of 9,10‐dihydrophenanthrene and each is dominated by a progression in a single vibrational mode. The ion vibrational spectrum is obtained using zero electron kinetic energy photoelectron spectroscopy (ZEKE‐PES) and the I.P. is determined to be 63 645 cm⁻¹. Semiempirical calculations including normal modes analysis were used to determine the vibrational motion responsible for the observed progression. The vibration is primarily a phenyl torsion, but is more complicated than a simple rigid motion. The specific shape of the potentials are determined from the frequencies of the observed vibrations and the relative shifts are obtained from a Franck–Condon analysis. The problem is solved using a one dimensional potential in the normal coordinate. A fluorescence depletion experiment is used to confirm the single‐welled nature of the potential energy surfaces. The phenyl dihedral angles are found to be 18°, 6°, and 14° in the ground, S₁, and cation ground electronic states, respectively.