Development and implementation of an in situ blackbody infrared radiation source in an FT-ICR mass spectrometer.

摘要

A high temperature source contained in an ICR cell is designed to perform blackbody irradiation dissociation studies to characterize reaction dynamics of gas-phase ions. Unimolecular dissociation reactions of gas-phase ions are used to generate thermochemical data, i.e. Arrhenius activation energies and relative A-factors, to characterize reaction mechanisms of gas-phase ions formed from electron impact ionization. In addition to thermal activation, collisional activation is used as a comparative means to induce chemical reactions of gas-phase ions.;Localization of the blackbody heat source has greatly increased the temperature envelope of experimental capabilities in a FT-ICR mass spectrometer. Experiments are routinely performed at temperatures in excess of 1000 K without adversely effecting the cryogenics of the superconducting magnet. Results demonstrate the ability of the heated wire ion-guide (WIG) cell to vibrationally excite gas-phase ions sufficiently to overcome activation barriers in excess of 1.5 eV. The WIG cell has shown to be extremely efficient requiring irradiation times of only ca. 20-seconds to attenuate the initially formed reactant ion population to 20% of its ion abundance at the onset of irradiation.;Performing high temperature studies in an ICR cell enables competition between unimolecular and bimolecular reactions. Both temperature and neutral reagent pressure may be varied to study competition between multiple reaction channels. The low operating pressures (between 1 x 10-8 and 4 x 10-7 torr) of the ICR-cell serve two functions, (i) reduce collisional contribution to increasing the trapped ions internal energy and (ii) providing a measure of control on the ion-neutral collision rate. Measurements of product ion abundances that arise from competing reaction channels are used to characterize the structure and/or energetics initially formed by precursor ions.