Cavity ring-down spectroscopy and vibronic activity of benzo[ghi]perylene

Abstract

Gas-phase cavity ring-down spectroscopy of jet-cooled benzo[ghi]perylene (C22 H12) in the 26 950-28 600- cm-1 spectral range is reported for the first time. This study is part of our extensive laboratory astrophysics program for the study of interstellar polycyclic aromatic hydrocarbons. The observed spectrum shows an intermediate level structure and significant broadening and is associated with the vibronically coupled S1 (A11) ← S0 (A11) and S2 (B11) ← S0 (A11) electronic transitions. Time-dependent density-functional calculations were performed to calculate the energetics, vibrational frequencies, and normal coordinates of the S1 and S2 states. A simple vibronic model was employed to account for the vibronic interaction between the vibronic levels of the S1 and S2 states. The calculated vibronic spectrum is found to be in good agreement with the experimental spectrum. © 2005 American Institute of Physics.