Z. Herman

Surface-induced reactions and decomposition of the benzene molecular ion C6H6+: Product ion intensities, angular and translational energy distributions

Abstract Surface-induced decomposition of benzene molecular ions (impact energy range 19–30 eV) and hydrogen atom abstraction from surface adsorbates leading to the production of a protonated benzene ion, were investigated using two different types of scattering apparatus. In addition to determining relative abundances of the product ions (mass spectra), we have measured the angular and translational energy distributions of the major product ions. All product ions show a strongly inelastic scattering behavior, with a maximum in translational energy distribution at 2–6 eV and a maximum in angular distribution at angles (70–75°) lower than the specular angle (90°). For the projectile ion, besides inelastic scattering reactions, we also observed an elastic scattering channel of substantial abundance exhibiting its maximum at scattering angles (55–60°) lower than that for the other scattered ions. Differences in the translational energy spectra for C 6 H 6 + and C 6 H 7 + were used to deduce the reaction sequences leading to the various fragment ions observed in the product ion mass spectra.

Dynamics of chemical reactions of doubly-charged ions. CF2D+ formation in collisions of CF22+ and D2

Abstract The dynamics of the formation of the chemical rearrangement product CF 2 D + and the charge transfer product CF 2 + in collisions of the dication CF 2 2+ with D 2 was investigated in a crossed-beam scattering experiment at a collision energy of 0.6 eV (c.m.). The scattering diagrams obtained show that both products are formed in impulsive processes in which Coulomb repulsion between two singly charged products, CF 2 D + + D + and CF 2 + + D 2 + , respectively, plays a dominant role. The energy partitioning of the total energy available in these highly exoergic processes is about half in the relative translation and about half in the internal energy (electronic and/or vibrational).

Dynamics of chemical and charge transfer reactions of molecular dications: beam scattering and total cross section data on CF2D+ (CF2H+), CF2+, and CF+ formations in CF22+ + D2(H2) collisions

Abstract Dynamics of formation of the chemical rearrangement product CF 2 D + , the charge transfer product CF 2 + , and the dissociative products CF + and CFD + in collisions of the molecular dication CF 2 ++ with D 2 was investigated in crossed beam scattering experiments over the collision energy range 0.3–1.0 eV (center of mass). The scattering data show that coulomb repulsion between two singly charged products, CF 2 + + D + and CF 2 + + D 2 + , plays a dominant role in the nondissociative processes. A large fraction of the energy available (about 6 eV in the chemical reaction, about 4 eV in the charge transfer) goes into relative translational energy of the products. Relative total cross sections for formation of the nondissociative and dissociative products in collision of CF 2 ++ with D 2 and H 2 were determined over the collision energy range of 0.2–3.6 eV. The shape of the relative velocity dependence of the cross section for CF 2 + formation can be described by a simple model based on the Landau-Zener formalism. The data suggest that the dissociative product CF + is formed prevailingly in a subsequent dissociation of the charge transfer product CF 2 + . A potential surface model is described which accounts for competition of various processes in dication–neutral collisions.

Surface-induced reactions of acetone cluster cations

The occurrence of two different chemical reactions initiated by the surface impact of acetone dimer, trimer, and tetramer cations (energy 20–70 eV) on a stainless-steel surface (covered with hydrocarbons) was observed. The reaction product is the protonated acetone ion, formed in (i) an intracluster ion–molecule reaction, and in (ii) a hydrogen pickup reaction of the cluster ion with the surface material. Only the monomer product ions (and small amounts of their dissociation products) could be observed; the spectra did not show any presence of clustered product ions. A simple model based on the Brauman double-well potential is suggested to explain the formation of the two product ions. In accordance with predictions from molecular dynamics simulations, this appears to be the first observation of competitive chemical reactions of a cluster ion driven by energy transfer in a surface collision.

Energy partitioning in collisions of slow polyatomic ions with carbon surfaces

Abstract Energy transfer in collisions of slow polyatomic ions with carbon surfaces (Tore Supra carbon tile and highly oriented pyrolytic graphite) was investigated over the incident energy range 10–23 eV. Mass spectra and translational energy and angular distributions of product ions were used to determine the partitioning of the incident energy of the projectile ion into internal excitation of the projectile, product translational energy, and fraction absorbed by the surface. The ethanol molecular ion was used as a model polyatomic ion. For the incident angle of 60° (with respect to the surface normal) the peak values of the respective energy fractions were 6% for excitation of the projectile, 24%–28% for product ion translational energy, and 70%–66% absorbed by the surface. Similar values for energy transfer were found earlier for energy transfer at stainless steel surfaces covered by hydrocarbons and surfaces covered by a self-assembled monolayer (SAM) of C 12 alkane chains. The occurrence of chemical reaction products (protonated ethanol and its fragment ions) formed by H-atom transfer from the surface material for all the above mentioned surfaces (the carbon surfaces, stainless steel with a hydrocarbon layer, alkane SAM) indicated that the carbon surfaces were covered with a layer of hydrocarbons, too, and thus the present results provide information of interest for energy transfer on carbon tiles covered with hydrocarbon films used in fusion research.

Surface-induced dissociation of singly and multiply charged fullerene ions

Collisions of singly and multiply charged ions C60z+ (z=1,2,3,4,5) with a hydrocarbon-covered stainless steel surface have been investigated; product ions of fragmentation and pickup reactions were determined as a function of the collision energy (100–500 eV) and the projectile charge z. All ions scattered off the surface are singly charged. The extent of fragmentation increases with the collision energy and the projectile charge. However, the increase of fragmentation with the charge of the projectile is less pronounced than expected from a full conversion of electronic energy, gained in the neutralization process, into internal energy of the ion.

Low energy reactive and dissociative collisions of the acetone cation CH3COCH3+ and its fragment ion CH3CO+ with a surface

Abstract The interaction of the parent acetone cation CH3COCH3+ and its ionic fragment CH3CO+ with a stainless steel surface covered with hydrocarbons has been studied as a function of the collision energy from about 0 up to 50 eV. In the case of CH3COCH3+ as projectile ion, the collisional interaction with the surface leads to the formation of protonated acetone and with increasing collision energies to fragment ions originating from both the protonated acetone ion (in particular, the production of CH2OH+) as well as the parent ion. These results have been confirmed using deuterated acetone ions. In the case of collisions of CH3CO+ with the surface only simple dissociative reactions of the projectile ion are observed.

Surface-induced dissociations and reactions of acetonitrile monomer, dimer and trimer ions

Dissociations and reactions induced by impact of acetonitrile monomer ions (CH3CN+, CD3CN+), dimer ions [(CH3CN)2+, (CD3CN)2+] and trimer ions [(CD3CN)3+] on a hydrocarbon-covered stainless-steel surface were investigated over the projectile energy range of 3–70 eV. Both simple dissociations of the projectile ion and chemical reactions of H-atom transfer from the surface material (followed by dissociations of the protonated projectile ion formed) were observed for the monomer ions. Results obtained for the dimer ions (CD3CN)2+ indicate the formation of the protonated acetonitrile ions via surface-induced reactions in two ways: (i) an intracluster ion–molecule reaction followed by dissociation to form CD3CND+, and (b) a hydrogen pick-up reaction from the surface material during the interaction of the dimer ion with the surface leading to CD3CNH+. A simple model based on the Brauman double-well potential—suggested earlier to explain the occurrence of analogous reactions in acetone cluster ion/surface intera...

Surface-induced chemical reactions of cluster ions: competitive processes of protonated acetone formation in acetone dimer–surface collisions

Abstract In low energy collisions (10–50 eV) of acetone dimer ions with a stainless steel surface (covered with hydrocarbons) we have been able to observe the occurrence of two different chemical reactions initiated by the surface impact and leading to the protonated acetone ion, namely (1) an intracluster ion–molecule reaction, and (2) a hydrogen pick-up reaction of the cluster ion with the surface material. In accordance with predictions from molecular dynamics simulations, this appears to be the first observation of competitive chemical reactions of a cluster ion driven by energy transfer in a surface collision.

The role of internal energy of polyatomic projectile ions in surface-induced dissociation

Abstract The effect of initial internal energy on the extent of surface-induced fragmentation was investigated in a tandem mass spectrometer for CH 3 + and CH 4 + ions prepared in different ion sources. The different initial internal energy content had a considerable effect on the extent of fragmentation of the surface-excited projectile ions: ions from a Nier source with a large amount of initial internal energy fragmented at much lower collision energies than internally relaxed projectile ions from a Colutron source. A quantitative estimation of this effect showed that the initial internal energy content of the projectile ions was entirely preserved in the projectile ion during the ion/surface collision.