Effects of kinetic energy and collision gas on measurement of cross sections by Fourier transform ion cyclotron resonance mass spectrometry

Linewidth Pressure Measurement: A New Technique for High Vacuum Characterization

“…This is in contrast to the CRAFTI cross sections for larger molecular ions we reported earlier [9,16], which generally increase with increasing kinetic energy. We believe the increase occurs because of increasing contributions to the CRAFTI cross section from collision-induced dissociation as kinetic energy increases.…”

“…Because few kinetic energy-resolved ion-neutral collision cross sections in the energy range appropriate for FTICR measurements are available, currently only a few options are available for calibrating LIPS. However, CRAFTI techniques [9,16] offer a means of measuring collision cross sections in gases other than Ar, as well as their kinetic energy dependence in the appropriate energy range, so that more options should soon become available. In addition, Barker-Ridge theory [17] could be used to estimate cross sections for other combinations of ions and neutral collision gases, making LIPS measurements possible for a wider range of systems, with the caveat that some error will be introduced because the kinetic energies of the ions in these experiments are not thermal.…”

“…We recently introduced a new method of measuring collision cross sections using an FTICR instrument (cross sectional areas from analysis of Fourier transform ion cyclotron resonance, or "CRAFTI") [9,16]. In FTICR experiments, ions are detected by using an applied rf pulse to excite them into phase coherent cyclotron motion, and then detecting the resulting image current induced by the coherently orbiting ions.…”

“…In FTICR experiments, ions are detected by using an applied rf pulse to excite them into phase coherent cyclotron motion, and then detecting the resulting image current induced by the coherently orbiting ions. CRAFTI measurements are based on the dependence of full width at half maximum (FWHM) FTICR linewidths on collisions that dephase the coherently orbiting ions (under pressurelimited conditions), and depend inversely on the neutral collision gas number density (n n ), as shown in (1) [9,16].…”

“…This is convenient because our primary application is pressure measurements in support of CRAFTI cross section determinations, and Ar is our collision gas of choice [16]. The purpose of this paper is to demonstrate this new method of measuring pressures that does not rely on ion current measurements, specifically to show that FTICR linewidth measurements can be used to accurately measure absolute pressures in the trapping cells of FTICR instruments.…”