Molecular beam spectroscopy of molecules with low volatility via laser desorption from thin films containing particulate silver

Abstract

A new polymer matrix containing particulate silver has been developed for the introduction of analytes with low or negligible volatility into molecular beams via laser desorption. These silver-containing film matrices (SCFM) permit stable desorption to proceed for extended periods (ca. approximately 10 h) and have been applied successfully to the nondestructive volatilization of a number of amino acids and a transition-metal compound. Analytes can be extracted directly from solution onto the SCFM surface by simply dipping the film into the solution and then air-drying the film. The laser desorption apparatus, when coupled to a supersonic molecular beam/laser ionization time-of-flight mass spectrometer, permits the detection of the analytes at femtogram levels. Furthermore, we have developed a reel-to-reel tape transport device that allows extended usage of the analyte-loaded SFCM, thereby permitting the measurement of wavelength-scanned mass-selected resonance-enhanced multiphoton ionization spectra of analytes with low or negligible volatility. We demonstrate this application with the aromatic amino acids L-tryptophan and L-phenylalanine. The degree of cooling achieved in the molecular expansion is shown to be comparable with that achieved using conventional beam sources, and the desorption yield is sufficiently stable for high-quality spectra to be measured.