| With the introduction of soft ionization techniques, such as electrospray ionization, large labile molecules now can be readily transferred to gas phase, and a new area in gas-phase chemistry of biomolecules was opened. The traditional method of studying ion energetics is to deposit a known amount of energy into an ion by using photons of a given frequency or transferring a specific amount of collisional energy. These approaches, however, are inefficient for large molecules because of the kinetic shift effect resulting from their many degrees of freedom.; The most accurate and versatile method for probing gas-phase energetics for large ions is blackbody infrared radiative dissociation (BIRD). Nevertheless, BIRD cannot be operated in pulsed format making it difficult to couple with other ion characterization techniques. In addition, the temperature range of BIRD is limited based on how hot the magnet bore and vacuum chamber components can be heated. Chemical systems which dissociate quicker than internal energy equilibration or those dissociate too slow at the highest accessible temperature cannot be accurately measured by BIRD.; Several dissociation techniques are developed here for energetic studies. A thermal jacket which encloses the FT-ICR ion cell is built. It can be cooled by liquid nitrogen, therefore extending the range of BIRD to colder temperatures to study fragile ions, such as highly hydrated magnesium and calcium ions. In developing a broadband pulsed dissociation technique, six tungsten filaments which can be resistively heated are attached to an ion cell. Photons emitted from filaments promote dissociation of molecular ions of acetophenone and n-butylbenzene, protonated leucine enkephalin and doubly protonated bradykinin. The visible photons emitted from the heated filaments play an active role in the dissociation process of n-butylbenzene as they promote the formation of m/z 91 ions, an ion not observed using just infrared radiation either generated thermally or with a CO2 laser. SO42-(H 2O)n; n = 3--17, are examined using three dissociation techniques: BIRD, infrared laser, and collisional-induced dissociation. Experimental results indicate that the elimination of water molecule is entropically favorable but energetically unfavorable compared to the charge separation dissociation via proton transfer. Moreover, the BIRD kinetics show unusual stability for the clusters n = 6 and 12, which suggests changes in structural conformation for these clusters. The new techniques described here open up new possibilities for studying chemical systems which are difficult to examine by other methods, and studying chemical reactions using these new techniques shed new light to the reaction mechanism. |
