A Multicoincidence Study of Fragmentation Dynamics in Collision of γ‐Aminobutyric Acid with Low‐Energy Ions

Abstract

Fragmentation of the γ-aminobutyric acid molecule (GABA, NH(2)(CH(2))(3)COOH) following collisions with slow O(6+) ions (v≈0.3 a.u.) was studied in the gas phase by a combined experimental and theoretical approach. In the experiments, a multicoincidence detection method was used to deduce the charge state of the GABA molecule before fragmentation. This is essential to unambiguously unravel the different fragmentation pathways. It was found that the molecular cations resulting from the collisions hardly survive the interaction and that the main dissociation channels correspond to formation of NH(2)CH(2)(+), HCNH(+), CH(2)CH(2)(+), and COOH(+) fragments. State-of-the-art quantum chemistry calculations allow different fragmentation mechanisms to be proposed from analysis of the relevant minima and transition states on the computed potential-energy surface. For example, the weak contribution at [M-18](+), where M is the mass of the parent ion, can be interpreted as resulting from H(2)O loss that follows molecular folding of the long carbon chain of the amino acid.

Determination of Energy-Transfer Distributions in Ionizing Ion-Molecule Collisions

“…Therefore, a detailed knowledge of the response of complex molecular systems to ionization or excitation and its influence on chemical reactivity is still a relevant topic today [9,10]. In this context, recent combined experimental and theoretical works have been very valuable in providing pictures of the ion-induced ionization or fragmentation of complex molecular systems [7,8,11,12]. However, a meaningful comparison between experimental and theoretical results requires knowledge of the energy transferred in the collision, which is in fact represented by a wide energy distribution due to interactions at different impact parameters.…”

Fragmentation Dynamics of Doubly Charged Methionine in the Gas Phase

“…However, C−S breaks always appear to occur associated with complex processes where other C−C bonds are also broken. Table 1 lists two possibilities for the m/z pair (27,28). On the PIPICO map of Figure 2, this pattern is quite close to the diagonal and is not well-defined, most probably because the heavy and/or numerous neutral fragments all but destroy the momentum correlation.…”

“…m/z pair(28,47) can originate from the deferred charge separation following the departure of a neutral carboxyl group(Figure 3c):…”

Multiple electron capture, excitation, and fragmentation inC6+−C60collisions

“…The next START signal (i.e., the next switch of the extraction pulse voltage) defines the end of the previous event. With the event-by-event list obtained, we can build spectra as a function of the multiplicity [60]. Thus, considering the high transmission and detection efficiency of the setup and its operation under single-collision conditions, the 1-STOP spectrum contains stable C q+ 60 (at the μs timescale) intact fullerenes and C q+ n fragments resulting from C 2 emission of C q+ 60 [7].…”

“…This was unambiguously shown by the authors of Refs. [22,23], where the excitation energies of the fragmenting fullerenes in keV H + + C 60 → H − + C 2+ 60 and F 2+ + C 60 → F − + C 3+ 60 collisions were measured to be 50 eV. These results are important benchmark data for the validation of statistical models and molecular dynamics simulations, which have been commonly used to guide interpretations of experimental results [36,39,[43][44][45].…”