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Abstract No.: TuP-108
Session: Gas Phase Ion Chemistry
Presentation date: Tue, Aug 29, 2006
Presentation time: 14:30 – 16:00

Threshold Collision-induced Dissociation: Hydrogen-bonded Complexes of Carboxylic Acids

Kent M. Ervin1, Beike Jia1, Laurence A. Angel1

1 University of Nevada, Reno, United States

Correspondence address: Kent M. Ervin, University of Nevada, Reno, Department of Chemistry, 1664 N. Virginia St., MS 216, Reno, NV, 89557 United States.

Web site: http://www.chem.unr.edu/faculty/kme/

Keywords: Acids, Carboxylic; Bonding, Hydrogen; Cluster, Proton Bound; Collision-Induced Dissociation (CID).

Novel aspect: Threshold collision-induced dissociation on species with bidentate hydrogen bonding.

 

Guided ion beam tandem mass spectrometry methods are used to study the hydrogen-bonded complexes of some simple carboxylic acids including formic acid, acetic acid, and benzoic acid. Proton-bound heterodimer anions composed of the carboxylic acid and a basic reference anion are synthesized using a microwave discharge in a flow tube reactor (flowing afterglow). In energy-resolved threshold collision-induced dissociation experiments, the mass-selected heterodimer anions are collided with an inert target gas under well-controlled conditions in a radio-frequency octopole ion beam guide. The dissociation cross sections and product branching ratios as a function of the available energy are modeled using statistical rate theory, either RRKM or phase space theory. These experiments yield the gas-phase acidity of the carboxylic acid relative to the reference species. Bidentate hydrogen bonding between two carboxylic acid functional groups is considered experimentally and theoretically via calculations of the potential energy surfaces. A local thermochemical network is constructed to determine the absolute gas-phase acidities, and the negative ion thermochemical cycle is used to derive neutral RCOO-H bond dissociation energies.