SIMULATED INFRARED-EMISSION SPECTRA OF HIGHLY EXCITED POLYATOMIC-MOLECULES - A DETAILED MODEL OF THE PAH-UIR HYPOTHESIS

A detailed description of the polycyclic aromatic hydrocarbon (PAH)/un identified infrared band (UIR) mechanism is presented in which experim ental spectral bandshape functions are used to simulate IR emission sp ectra for individual molecules. These spectra are additively superimpo sed to produce a conglomerate spectrum representative of a family of P AH molecules. Ab initio vibrational frequencies and intensities for ni ne PAHs (neutral and cationic) as large as ovalene are used in conjunc tion with measured bandshape and temperature-dependent redshift data t o simulate the UIR bands. The calculated spectra of cations provide a closer match to the UIRs than do those of the neutrals. However, the P AH cations used in the simulations fail to reproduce the details of th e UIR emission spectra. The discrepancies are potentially alleviated i f both larger PAHs and a greater number of PAHs were included in the s imulation.