PHOTOIONIZATION QUANTUM YIELDS OF POLYCYCLIC AROMATIC-HYDROCARBONS

The gas-phase photoionization yield curves were measured for 6 PAHs: b enzene, naphthalene, azulene, anthracene, phenanthrene and benz[a]anth racene, over the photon energy range 5-25 eV, and the corresponding ph otoionization quantum yields gamma(lambda) were derived as a function of wavelength. The results are used to propose ''rules of thumb'' for determining the value of gamma(lambda) of PAHs at any photon energy ab ove the ionization threshold. Effects of molecular size on gamma(lambd a) and on the ease of photoelectron ejection are discussed in the cont ext of determination of gamma(lambda) for the full range of PAHs expec ted in the ISM. These data are required for modelling PAH destruction and ionization rates in circumstellar and interstellar media and also for understanding the energy budget of the diffuse interstellar medium .