Control of chemical reactions and synthesis by low-energy electrons

Abstract

Controlling the outcome of reactions is a central issue of chemical research. Physical tools can achieve this if they are able to precisely dissociate specific bonds of a molecule. However, to control synthesis, such tools must induce the formation of new bonds between two reactants to yield a more complex product. In the ideal case of an atom efficient synthesis, this product would contain all or at least most of the initial material. An electron beam is a physical tool that is capable of preparing molecules in reactive states or, at low electron energies, of initiating highly selective bond dissociation. The resulting fragments in turn can react with other molecules to yield stable products. This tutorial review focuses in particular on such low-energy electron-initiated molecular syntheses and their applications in the modification of surfaces. It thus emphasizes strategies towards the controlled and predictable formation of more complex products from small reactants initiated by interaction with low-energy electrons either through selective bond dissociation or formation of specific reactive molecular species. However, selective bond dissociation is not always desirable. This is briefly illustrated by the case of electron beam induced deposition where additional strategies may be required to control product formation.

Electron‐Induced Hydration of an Alkene: Alternative Reaction Pathways

“…[3,4] However,i nc ondensed phase where polarization forces stabilize the charge,the radical anion may also survive. [3,4] As neutral excitation processes are absent below roughly 4eVinboth C 2 H 4 and H 2 O, [11] such anionic processes must be responsible for the ethanol yield at low E 0 values. DEA processes for H 2 Oi nt he gas phase occur around 7eV, 9eV, and 11 eV [12] and thus above the range of E 0 values concerned here.Noproduction of OHC radicals occurs below 5eV.…”

In situgrowth of Ag nanoparticles onα-Ag2WO4under electron irradiation: probing the physical principles

“…It has been shown that these electron beam induced processes can be performed on almost any kind of substrate [28]. Recently, Bohler et al [29] reviewed low-energy, electron-initiated molecular syntheses and their applications in the modification of surfaces. In summary, irradiation of materials with an electron beam in a TEM can be used to fabricate nanomaterials and to investigate their morphology, structure, and chemical transformations.…”

Low energy electron induced reactions in fluorinated acetamide – probing negative ions and neutral stable counterparts*

“…In the condensed phase experiments, a multilayer film of TFAA is deposited on a cryogenic metal substrate and then irradiated by an electron beam at a particular energy. Reactions in the condensed material are then probed by thermal desorption spectrometry (TDS) [2][3][4]. The gas phase experiments are carried out under single collision conditions, i.e., the recorded fragment ion is the result of a single collision between an electron and the molecule resulting in resonant electron attachment and the subsequent unimolecular decomposition of the transient negative ion.…”

“…a e-mail: kopyra@uph.edu.pl electrons [4][5][6], the condensed environment may also retain immediate products of the dissociative electronmolecule encounter. DEA reactions have so far been studied on many compounds and, in particular, on halogenated molecules because of their well-documented electron scavenging properties [1,7].…”