Kinetics and mechanism of the collision-activated dissociation of the acetone cation

Abstract

For center-of-mass collision energies Ecm = 1-60 eV, the major fragment ions for the collision-activated dissociation (CAD) of the acetone cation are the acetyl cation (m / z 43; absolute branching ratios of 0.96-0.60) and the methyl cation (m/ z 15; absolute branching ratios of 0.02-0.26); the absolute total cross-sections were 24-35) Å(2). The breakdown curves (viz, plots of the absolute branching ratios versus Ecm) show complex, complementary energy dependences for production of MeCO(+) and Me(+), indicating apparent closure of the Me(+) channel for Ecm > 30 eV. Our observations are consistent with a competition between three fast, primary (direct) reactions, each of which opens sequentially at its respective threshold energy (viz, reactions 8, 10, and 8'). [Formula: see text] [Formula: see text] [Formula: see text] That is, the breakdown curves for MeCO(+) and Me(+) (and other CAD fragments) are consistent with the interpretation by other authors that the collisional activation of the acetone cation involves electronic transitions, so that CAD occurs primarily from isolated electronic states (i.e., non-quasi-equilibrium theory (QET) behavior). For acetone we found a correspondence between the photoelectron-photoion-coincidence and CAD breakdown curves. This may indicate that collisional activation in non-QET systems corresponds to scattering angles that emphasize optically allowed transitions accessed by photoionization.

A multiphoton ionization study of acetone using time-of-flight mass spectrometry

“…where the ∆H is the reaction enthalpy, which is 0.83 eV for reaction (6) [17,19,40] and 3.3 eV for reaction (7) [16]. At 336.93 nm (3p x 1 A 2 origin), the available energy for reaction (6) is 2.85 eV and 0.38 eV for reaction (7).…”

Cryogenic micro-calorimeters for mass spectrometric identification of neutral molecules and molecular fragments

“…Many studies exist on CID and ETD of the acetone radical [77][78][79][80][81] . However, the vast majority of the techniques used collected only charged reaction products.…”

Determination of apparent decomposition threshold energies of lithium adducts of acylglycerols using tandem mass spectrometry and a novel derived effective reaction path length approach

“…Typically, collision energy and collision cell gas pressure are chosen to achieve 20–70% attenuation of the precursor ion abundance, and the products from the collision‐induced fragmentation are thereby formed under multiple collision conditions. However, in energy‐resolved mass spectrometry studies29–36 where the specific kinetics of the fragmentation pathways are of interest, single collision conditions (∼10% attenuation of precursor beam) are employed in the QhQ mass spectrometer, and a series of spectra are obtained at increasing activation energies controlled by the energy offset of the central hexapole. During energy‐resolved mass spectrometry studies, a wealth of information is being collected which can be used to qualitatively describe the unimolecular fragmentation pathways through the use of breakdown graphs, where the percentage of the total abundance for each product ion is plotted versus collision energy.…”