LASER MASS-SPECTROMETRIC ANALYSIS OF POLYCYCLIC AROMATIC-HYDROCARBONSWITH WIDE WAVELENGTH RANGE LASER MULTIPHOTON IONIZATION SPECTROSCOPY

In many analytical techniques, 1+1 resonance-enhanced multiphoton ioni zation (1+1 REMPI) is used because it is an efficient and optically se lective soft ionization method. While 1+1 REMPI of jet-cooled molecule s has been extensively studied, little has been reported so far about this mechanism as it is used in analytical techniques, that is, in the cases where the molecules are not jet-cooled and where widely varying ionization wavelengths are employed. We used two-step laser mass spec trometry (L2MS) to study the wavelength (238-310 nm) dependence and th e laser pulse energy dependence of the ion yield for 17 polycyclic aro matic hydrocarbons (PAHs). We discuss how these data allow prediction of the efficiency of 1+1 REMPI for a given compound. These advances op en new perspectives for better understanding the L2MS spectra obtained directly from complex mixtures such as environmental samples.