Simultaneous Detection of (H_(2))~(+) with Larger Ions Using Fourier Transform Mass Spectrometry

摘要

Laser-induced desorption coupled with Fourier transform mass spectrometry (FTMS) has proven to be a useful technique for the studies of chemical reactions that occur in monolayers adsorbed on solid surfaces. The high sensitivity and ultrahigh mass resolution have been extremely useful in the study of reactions in complex monolayer mixtures made up of molecular species with m/z between 15 and 1000. For studies of hydrocarbon reactions on surfaces, such as would be useful for fundamental studies of catalytic processes on transition metal surfaces, it is extremely useful to be able to detect molecular hydrogen desorbing from a surface simultaneously with higher molecular weight reactants and reaction products. However, simultaneous detection of molecular hydrogen and higher molecular weight species presents a unique challenge for FTMS, as a result not only of the high cyclotron frequency of the (H_(2))~(+) molecular ion but also as a result of z-ejection and proton- and charge-transfer reactions. We characterize the issues associated with direct simultaneous detection of molecular hydrogen using FTMS and demonstrate the experimental conditions necessary for the simultaneous detection of hydrogen and larger species such as argon and cyclohexane.