Laboratory experiments on the determination of polycyclic aromatic hydrocarbon coverage of submicrometer particles by laser-induced aerosol photoemission

Abstract

First measurements of laser-induced photoelectric charging of submicrometer particles with different polycyclic aromatic hydrocarbon (PAH) coatings are presented. Pure carbon and NaCl particles were generated, and a monodisperse fraction was selected for subsequent coating with a PAH. The growth of the particles due to PAH adsorption or condensation was controlled with a screen type diffusion battery with a resolution better than 1 nm. These aerosols were irradiated with an excimer-laser-pumped dye laser that was frequency-doubled with a BBO crystal. Once photoelectrons were emitted, the remaining positively charged particles were detected with an aerosol electrometer. Wavelengths between 207.5 and 241 nm were investigated. Pure NaCl particles showed a clearly nonlinear behavior when irradiated with increasing energy density of the laser at a fixed wavelength, while pure carbon particles showed a linear behavior. The spectral dependences of the charging of NaCl and carbon particles are given for different PAH submonolayer coatings. Emission of coated NaCl particles is enhanced for all the PAHs, while in the case of carbon particles different PAHs had a different influence on the emission.