ANALYSIS OF THE TORSIONAL POTENTIAL OF 9,10-DIHYDROPHENANTHRENE IN 3 ELECTRONIC STATES - S0, S1, AND CATION GROUND-STATE

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-degrees, 6-degrees, and 14-degrees in the ground, S1, and cation ground electronic states, respectively.