MULTIPHOTON IONIZATION SPECTROSCOPY IN SURFACE-ANALYSIS AND LASER-DESORPTION MASS-SPECTROMETRY

The application of resonance-enhanced multiphoton ionization (REMPI) s pectroscopy for the ultrasensitive detection of molecules originating from laser desorption experiments performed on a variety of substrates is reviewed. Laser-induced desorption from surfaces is capable of pro ducing intact gas-phase molecules, even from polar, non-volatile, high -molecular-weight and thermally labile substances. REMPI is a highly e fficient and optically selective ionization method, which, coupled wit h laser desorption allows the direct chemical analysis of complex mixt ures, without the need for previous sample purification and separation steps. The use of REMPI spectroscopy is discussed in two contexts: (1 ) for the direct chemical analysis of complex mixtures, e.g., environm ental samples, by laser desorption/laser postionization mass spectrome try and (2) for measurements of internal state distribution of molecul es laser-desorbed from sub-monolayers surface films to gain insight in to the laser desorption mechanism.