Translational to Vibrational Energy Conversion during Surface-Induced Dissociation of N-Butylbenzene Molecular Ions Colliding at Self-Assembled Monolayer Surfaces

Abstract

Translational to vibrational (T-->V) energy conversion in the course of inelastic collisions of n-butylbenzene molecular ions with thiolate self-assembled monolayer (SAM) gold surfaces is studied to better understand internal energy uptake by the hyperthermal projectile ions. The projectile ion is selected by a mass spectrometer of BE configuration and product ions are analyzed using a quadrupole mass analyzer after kinetic energy selection with an electric sector. The branching ratio for formation of the fragment ions m/z 91 and m/z 92, measured over a range of collision energies, is used to estimate the average internal energy with the aid of calculations based on unimolecular dissociation kinetics [Rice-Ramsperger-Kassel-Marcus (RRKM) theory]. The measured T-->V conversion efficiencies (the fraction of the laboratory kinetic energy converted into internal energy) are 11 approximately 12% for dodecanethiolate SAM (H-SAM) and 19 approximately 20% for 2-perfluorooctylethanethiolate SAM (F-SAM), respectively, over ranges of a few 10s of eV. The values are similar to those reported earlier for other thermometer molecules undergoing surface collisions. Chemical sputtering leading to ionization of the surface is a prominent feature of the surface-induced dissociation (SID) spectra of n-butylbenzene acquired using the H-SAM surface but not the F-SAM surface because of the lower ionization energy of the former.

Ion/surface reactions and ion soft-landing

“…In most cases, hyperthermal energy collisions provide highly useful chemical information on the ions and surfaces (provided that the surfaces are not chemically inert); the information includes insights into structures and reactivities. Fundamental aspects of ion/surface collision processes include studies of energy partitioning during inelastic collisions, in particular the transfer of translational energy to vibrational energy (T -V), 32 the recently recognized non-statistical dissociation mechanisms (ion shattering) 33 and of course, comparisons of reactivity at interfaces with gas-phase and solution-phase analogs.…”

“…It is clear that the internal energy transferred increases with collision energy, that it increases roughly in proportion to the translational energy and that the energy transfer efficiency (% T-V) is greater for the fluorine terminated self-assembled monolayer (F-SAM) surface (20%) than the hydrogen-terminated self-assembled monolayer (H-SAM) (12%) surface. 32 b. Charge inversion Among the many phenomena associated with gas-phase collisions of keV energy ions are charge inversion, electron transfer and charge stripping processes in which incident positively charged ions are converted into negatively charged ions and vice versa.…”

Surface-Induced Dissociation: An Effective Method for Characterization of Protein Quaternary Structure

“…7,15 The use of these easy-to-prepare surfaces has persisted, although several other surface types have been utilized. 16–24 These SAMs provide a large effective mass for collision of projectile ions, the fluorocarbon chains are relatively rigid so that they don’t severely dampen the energy of the colliding projectile, and the fluorocarbon resists facile electron transfer to the incoming ions. Surface targets, in contrast to the typical gaseous targets such as Ar that are used for the more common activation method collision-induced dissociation (CID), have proven to be exceptionally useful for the characterization of protein complex quaternary structure.…”

Self-assembled monolayer-assisted mass spectrometry

“…The different results show that the E kin / E int > 20% for F-SAMs and around 15% for H-SAMs (as for stainless steel surfaces). 43,45,51,55,58,60,61 The influence of the alkyl chain orientation on the nature of the ions observed on the ion-surface collision mass spectra has been disclosed with the used of oddchain-length and even-chain-length films. 53 For the former, the last C-C bond is more parallel to the plane of the surface whereas the last film places the hydrogen atoms in more favorable position for reacting with the incident ion beam.…”