Dissociation Kinetics of Lithium Acetate and Lithium Formate Ion Clusters from Molecular Dynamics Simulation
Poster Number
3A
Introduction/Abstract
Electrospray ionization mass spectrometry (ESI MS) is an important analytical technique used to obtain structural and molecular information about large analyte molecules. In an ESI mass spectrum, only the charged species are observed. Computationally, the abundances of the neutral species may be observed in addition to the charged species, giving more data for analysis and interpretation.
Purpose
By simulating ESI mass spectral data over various temperatures, more insight on the ion decay kinetics can be gained.
Method
The two lithium ion clusters investigated are lithium acetate, Li+(CH3COOLi)n, and lithium formate, Li+(HCOOLi)n, with cluster sizes n=13 and n=12. Through simulation, abundance data was obtained for each fragment and its corresponding neutral product at temperatures ranging from 1100 K to 1300 K for each ion cluster size. The first-order kinetics was then investigated through the Arrhenius equation. First-order kinetics are assumed at the beginning of the reaction as initially all the fragments are products of the parent cluster and there are no other fragments to undergo secondary fragmentation near t=0.
Results
Magic number cluster ion n=3 and major neutral product n=2 are observed for lithium acetate and lithium formate clusters at both sizes. For lithium formate, the kinetics for the dissociation are similar across all temperatures for n=13 and n=12. The activation energies for the lithium formate ion clusters were calculated to have a difference of less than 100 J, which is in agreement with that is observed. For lithium acetate, the kinetics are only similar at lower temperatures (1100 K to 1200 K). As the temperature increases, the larger cluster at n=12 dissociates at a higher rate than n=13. The activation energies differed by more than 500 J for the lithium acetate cluster ion, implying that the n=12 cluster is less stable than the n=13 cluster despite having similar fragmentation patterns.
Significance
A lot more data can be obtained through simulations which can give more information about occurrences than cannot be observed, such as the abundances of neutral products in ESI MS. The simulated data agrees with experimental data, so the simulations can be used to confidently predict systems that have not been observed before.
Location
William Knox Holt Memorial Library and Learning Center, University of the Pacific, 3601 Pacific Ave., Stockton, CA 95211
Format
Poster Presentation
Poster Session
Afternoon
Dissociation Kinetics of Lithium Acetate and Lithium Formate Ion Clusters from Molecular Dynamics Simulation
William Knox Holt Memorial Library and Learning Center, University of the Pacific, 3601 Pacific Ave., Stockton, CA 95211
Electrospray ionization mass spectrometry (ESI MS) is an important analytical technique used to obtain structural and molecular information about large analyte molecules. In an ESI mass spectrum, only the charged species are observed. Computationally, the abundances of the neutral species may be observed in addition to the charged species, giving more data for analysis and interpretation.
