The performance of infrared (IR) spectroscopy of gas-phase ions in a commercially available 7 T Fourier transform ion cyclotron resonance mass spectrometer has been characterized. A pi-allyl-palladium reactive intermediate, [(pi-allyl)Pd(P(C6H5)3)2]+, involved in the catalytic allylation of amine is studied. A solution of this transition metal complex is electrosprayed, and the IR multiple photon dissociation (IRMPD) spectrum of the mass-selected ions is recorded in two spectral ranges. The fingerprint spectrum (650-1550 cm(-1)) is recorded using the Orsay free-electron laser, and the dependence of the IRMPD efficiency on laser power and irradiation time is characterized. The DFT-calculated IR absorption spectrum of the [(pi-allyl)Pd(P(C6H5)3)2]+ complex shows good agreement with the experimental spectrum. The pi-interaction between the palladium and the allyl moiety is reflected by the assignment of the IRMPD bands, and the observed allylic CH2 wagging modes appear to form a sensitive probe for the pi-interaction strength in metal-pi-allyl complexes. This spectral assignment is further supported by the analysis of the different IRMPD photofragmentation patterns observed at different photon energies, which are found to result from wavelength-specific photofragmentations. Nine peaks are well-resolved in the experimental spectrum, for which the bandwidth (fwhm) is on the order of 15 cm(-1). Resonances with a calculated IR intensity of 5 km/mol or larger are shown to be amenable for IRMPD, indicating an excellent sensitivity of our new experimental setup. Finally, the IR spectrum has also been recorded in the CH stretching region (2950-3150 cm(-1)) using a tabletop IR optical parametric oscillator/amplifier (OPO/OPA) laser source.

Tautomerism of the nucleobase uracil is characterized in the gas phase through IR photodissociation spectroscopy of singly hydrated protonated uracil created with tandem mass spectrometric methods in a commercially available Fourier transform ion cyclotron resonance mass spectrometer. Protonated uracil ions generated by electrospray ionization are re-solvated in a low-pressure collision cell filled with a mixture of water vapor seeded in argon. Their structure is investigated by IR photodissociation spectroscopy in the NH and OH stretching region (2500-3800 cm(-1)) with a tabletop IR laser source and in the 1000-2000 cm(-1) range with a free-electron laser. In both regions the IR photodissociation spectrum exhibits well-resolved spectral signatures that point to the presence of two different types of structure for monohydrated protonated uracil, which result from the two lowest-energy tautomers of uracil. Ab initio calculations confirm that no water-catalyzed tautomerization occurs during the re-solvation process, indicating that the two protonated forms of uracil directly originate from the electrospray process.