Neutralization of methyl cation via chemical reactions in low-energy ion-surface collisions with fluorocarbon and hydrocarbon self-assembled monolayer films

Abstract

Low-energy ion-surface collisions of methyl cation at hydrocarbon and fluorocarbon self-assembled monolayer (SAM) surfaces produce extensive neutralization of CH3+. These experimental observations are reported together with the results obtained for ion-surface collisions with the molecular ions of benzene, styrene, 3-fluorobenzonitrile, 1,3,5-triazine, and ammonia on the same surfaces. For comparison, low-energy gas-phase collisions of CD3+ and 3-fluorobenzonitrile molecular ions with neutral n-butane reagent gas were conducted in a triple quadrupole (QQQ) instrument. Relevant MP2 6-31G*//MP2 6-31G* ab initio and thermochemical calculations provide further insight in the neutralization mechanisms of methyl cation. The data suggest that neutralization of methyl cation with hydrocarbon and fluorocarbon SAMs occurs by concerted chemical reactions, i.e., that neutralization of the projectile occurs not only by a direct electron transfer from the surface but also by formation of a neutral molecule. The calculations indicate that the following products can be formed by exothermic processes and without appreciable activation energy: CH4 (formal hydride ion addition) and C2H6 (formal methyl anion addition) from a hydrocarbon surface and CH3F (formal fluoride addition) from a fluorocarbon surface. The results also demonstrate that, in some cases, simple thermochemical calculations cannot be used to predict the energy profiles because relatively large activation energies can be associated with exothermic reactions, as was found for the formation of CH3CF3 (formal addition of trifluoromethyl anion).

Collisions of Slow Ions C3Hn+ and C3Dn+ (n = 2–8) with Room Temperature Carbon Surfaces: Mass Spectra of Product Ions and the Ion Survival Probability

“…An analogous correlation to that in figure 5(a) was made earlier 26 with six ion projectiles of IE between 8.5 eV and 10.2 eV on self-assembled monolayer (SAM) films. the results for alkyl-terminated SAM are in very good agreement with the more abundant data in figure 5(a) for the carbon surface covered with background hydrocarbons.…”

“…the results for alkyl-terminated SAM are in very good agreement with the more abundant data in figure 5(a) for the carbon surface covered with background hydrocarbons. for cf 3 terminated SAM, 26 the survival probabilities were larger and the drop to low S a values seemed to occur at higher ionization energies of the projectile ions. increasing incident energy.…”

Differentiation of isomeric oxygenated adsorbates using low-energy ion/surface collisions

“…The relative fragment ion abundance in the SID spectra of C 5 H 5 N •+ ions occurs in the order HO-SAM < CH 3 O-SAM ∼ CH 3 CH 2 O-SAM and these two factors might be inter-related. The increased availability of H atoms at the CH 3 CH 2 O-terminated monolayer surface as compared to the HO-terminated monolayer surface is an alternative explanation which is also consistent with previous results for other systems [38,49].…”

Soft-landing preparative mass spectrometry

“…7 In 2002 Wysocki and coworkers investigated methyl cation neutralization on SAMs. 123 Here, the authors were able to combine experimental results with computational methodology to map out a two-dimensional energy map of CH 3 + as a function of distance from the surface. They reported that CH 3 + neutralization could occur by either direct electron transfer from the SAM or the formation neutral methane or ethane.…”

“…They reported that CH 3 + neutralization could occur by either direct electron transfer from the SAM or the formation neutral methane or ethane. 123 MD simulations, in particular Car-Parrinello MD, were used by Zeng and coworkers to investigate the transition from two-dimensional to three-dimensional structures of Au 10 . 124 Further, these transitions were applied to the catalytic oxidation of CO. A recent report by Kemper and Sinnott used classical atomistic MD to look at the deposition of terthiophene on hydrogen-terminated diamond.…”