Adsorption dynamics of bifunctional molecules: Allyl methyl ether on Si(001)

Abstract

The reaction dynamics of allyl methyl ether (AME) on Si(001) was studied by means of molecular beam techniques. The reaction of this bifunctional molecule comprising an ether and an alkene group was found to proceed via an intermediate state as deduced from the temperature dependence of the initial sticking probability s0. At constant surface temperature Ts, s0 decreases continuously with increasing kinetic energy Ekin, indicating a non-activated adsorption channel. Qualitatively and quantitatively, the energy dependence is almost identical to the adsorption dynamics of diethyl ether on Si(001). We attribute this to a similar nature of the intermediate state, which largely determines the adsorption dynamics. In consequence, this indicates a predominant role of the ether group and a minor influence of the C=C double bond on the adsorption dynamics of AME on Si(001).

Tip-Induced Dissociation of Diethyl Ether on Si(001)─Influence of Molecular Structure on Final Reaction Products

“…Indeed, in the picture of transient electron attachment to the antibonding σ* orbital, interaction with the positively charged D down orbital seems to be favorable. Note that this reaction thus clearly differs from commonly observed pathways of thermally activated reactions on Si(001) which often involve a silicon atom with filled dangling bond state and a nucleophilic attack at the organic molecule − as it is also the case for thermally induced ether cleavage. − …”

“…Ether molecules such as Et 2 O and tetrahydrofuran (THF) adsorb on Si(001) via a datively bound intermediate − (Figures and c). Thermal activation at surface temperatures T s > 150 K induces C–O cleavage in an S N 2-like fashion, leading to covalently bound final states. − Tip-induced excitation of surface-adsorbed THF on Si(001) was shown to lead to additional reaction products when compared to thermal activation: whereas thermal activation leads to one single final configuration, electronic excitation was found to lead to two additional final states (Figure ). For tip-induced ether cleavage of Et 2 O on Si(001), we observe a comparable excitation scheme as for THF but the final states of Et 2 O and THF after electronic excitation show distinct differences despite the similar excitation mechanism.…”

Chemoselective Adsorption of Allyl Ethers on Si(001): How the Interaction between Two Functional Groups Controls the Reactivity and Final Products of a Surface Reaction

“…Experiments on the adsorption dynamics of AME on Si(001) have shown a dominant influence of the datively bound intermediate of the ether group already in the initial adsorption step . At 90 K and below, we furthermore find the molecules to be bound via this datively bound intermediate state.…”

“…However, for AME on Si(001), molecular beam experiments have shown unambiguously that the reaction proceeds via an intermediate state . Thus, the situation is qualitatively different from the cyclooctyne systems.…”

“…The change in reactivity is therefore directly coupled to the additional C=C double bond in the allyl group, which increases the reactivity of the ether group with respect to ether cleavage on Si(001). Indeed, in earlier investigations on the adsorption dynamics and kinetics of AME on Si(001), it was found that the difference between binding energy and conversion barrier from the intermediate into the final state, E b – E a , is larger for AME/Si(001) when compared to DEE/Si(001). Assuming a similar binding energy for both molecules in the datively bound intermediate, this would indeed imply a lower conversion barrier and thus higher reactivity for AME/Si(001).…”