Gas Phase Infrared Spectroscopy of Selectively Prepared Ions

The first example of direct structural characterization of polyaromatic ions by coupling a Fourier transform ion cyclotron resonance mass spectrometer with an infrared free-electron laser is presented. Measurement of the IR spectra of selectively prepared ionic reactive intermediates is allowed by the association of the high peak power and wide tunability of the laser with the flexibility of the spectrometer, where several mass selection and ion reaction steps can be combined, as demonstrated in the case of iron cation complexes of hydrocarbons. The present experimental setup opens the way to understanding chemical reaction paths.

Figure 1

Photodissociation of $\mathrm{F}\mathrm{e}\mathrm{C}\mathrm{O}_5{}^{+}$: Remaining parent ion as a function of the number of macropulses for four laser average powers: 18, 56, 170, and 500 mW from top to bottom (a) and fragmentation efficiency E (see text) versus laser power (b)

Figure 2

Evolution of the parent and photofragment ions as a function of the wavelength using an average laser power of ca. 500 mW. Parent ions are ${\mathrm{F}\mathrm{e}\mathrm{C}}_4\mathrm{H}_8{}^{+}$ (a) and ${\mathrm{F}\mathrm{e}\mathrm{C}}_4\mathrm{H}_6{}^{+}$ (b).

Figure 3

IRMPD spectrum of ${\mathrm{F}\mathrm{e}\mathrm{C}}_4\mathrm{H}_8{}^{+}$ compared to the calculated bar spectrum and to a spectrum convoluted with a Lorentzian profile (dotted line). The left hand scale represents the IRMPD efficiency and the right one the calculated infrared intensities ($\mathrm{k}\mathrm{m}{\mathrm{m}\mathrm{o}\mathrm{l}}^{-1}$