title: Cavity ring-down spectroscopy and theoretical calculations of the S1(1B3u)<--S0(1Ag) transition of jet-cooled perylene.
abstract: As part of our long-term program to test the diffuse interstellar band-polycyclic aromatic hydrocarbon hypothesis, we have investigated the S(1)<--S(0) electronic transition of neutral perylene (C(20)H(12)) in a combined experimental and theoretical study. Jet-cooled perylene was prepared with a pulsed discharge slit nozzle and detected by cavity ring-down spectroscopy. A number of vibronic features were observed in the 24 000-24 900 cm(-1) spectral range. Density functional and ab initio calculations were performed to determine the geometries, harmonic vibrational frequencies, and normal coordinates of both the S(0) and S(1) electronic states. A rotational temperature of 52+/-5 K was derived from a rotational contour analysis of the vibronic band associated with the 0-0 transition. A Franck-Condon treatment was carried out to calculate the vibronic spectrum of the S(1)<--S(0) transition. A good agreement was found between the calculated and the experimental spectra. A vibrational assignment is proposed and six normal modes are identified. The contribution of neutral compact polycyclic aromatic hydrocarbons to the diffuse interstellar bands is briefly discussed.
authors.affiliation: Space Science Division, NASA Ames Research Center, Mail Stop 245-6, Moffett Field, CA 94035-1000, USA. x.tan@jhu.edu
authors.forename: Xiaofeng
authors.initials: X
authors.lastname: Tan
authors.forename: Farid
authors.initials: F
authors.lastname: Salama