Cleavage of the ether bond by electron impact: differences between linear ethers and tetrahydrofuran

Abstract

Dissociative electron attachment (DEA) to diethyl ether yielded primarily the C 2 H 5 O À ion, with a strong Feshbach resonance band at 9.1 eV and a weaker shape resonance band at 3.89 eV. Very similar spectra were obtained for dibutyl ether, with C 4 H 9 O À bands at 8.0 and 3.6 eV. Some of these primary ions subsequently lost H 2 and yielded weaker signals of the C 2 H 3 O À and C 4 H 7 O À ions. In contrast, DEA to the cyclic ether tetrahydrofuran (THF) yielded mainly a fragment of mass 41, presumably deprotonated ketene, at 7.65 eV. The low-energy band was missing in THF. H À with two bands at 6.88 and 8.61 eV, and an ion of mass 43 (presumably deprotonated acetaldehyde) with two bands at 6.7 and 8.50 eV were also observed. We propose that in the primary DEA step the C-O bond is cleaved in both the open-chain and the cyclic ethers. In the open-chain ethers the excess energy is partitioned between the (internal and kinetic) energies of two fragments, resulting in an RO À ion cool enough to be observed. The CH 2 (CH 2 ) 3 O À ion resulting from cleavage of the C-O bond in THF contains the entire excess energy (more than 6 eV at an electron energy of 7.65 eV) and is too short-lived with respect to further dissociation and thermal autodetachment to be detected in a mass spectrometer. These findings imply that there could be a substantial difference between the fragmentation in the gas phase described here and fragmentation in the condensed phase where the initially formed fragments can be rapidly cooled by the environment.

Partial cross sections for dissociative electron attachment to tetrahydrofuran reveal a dynamics-driven rich fragmentation pattern

“…The strongest heavy fragment with the mass 41 has been reported both by Sulzer et al [8] and by Ibanescu et al [31]. The shape and position of the band agrees very well with present results.…”

“…Comparison of the two mass spectra also shows that the peak with the mass 41 shifts to mass 46 upon deuteration of the precursor molecule. Thus its chemical composition is C 3 H 5 − , the allyl anion, instead of C 2 OH − , deprotonated ketene, as it was assigned in both previous mass-resolved studies [8,31]. The reason for their assignment was probably the fact that the formation of C 2 OH − is energetically more favorable.…”

“…The dissociative electron attachment channels in THF have also been the subject of several studies, Sulzer et al [8] and Ibanescu et al [31] reported yields of individual DEA fragments as a function of the electron energy and Aflattoni et al [32] measured total DEA cross section using a total ion collection instrument. Surprisingly, the first two studies only partially agree with each other: they agree on the occurrence of the (strongest) fragment with atomic mass 41, which was assigned by both groups to be the C 2 HO − anion.…”

Ion formation upon electron collisions with valine embedded in helium nanodroplets

“…In recent years interest in collisions of leptons, photons or heavier species with biomolecules has increased substantially [1][2][3][4][5][6] as the description of radiation damage of biological tissue remains incomplete at the molecular level. Apparently secondary species formed by high-energy radiation, such as electrons, radicals and ions, are responsible for the chemical transformation of biomolecules that accompanies severe radiation damage in cells, viz.…”

Low-energy electron scattering by tetrahydrofuran

“…In particular, low-energy electron interactions with tetrahydrofuran (THF), the simplest model of the furanose ring that links the phosphate groups in the DNA backbone, have been studied intensively by both experimental and computational [21,[24][25][26][27][28] methods. These studies have provided valuable information about processes relevant to understanding electron transport and reactivity in biological media, including vibrational [4,8,11,15,18] and electronic excitation [3,8,11,20,22,23], dissociative attachment [5,6,10,14,19], electron trapping and reactivity in condensed THF [7,11,13], and the elastic [8,[15][16][17]20] and total scattering [9,12,21] cross sections. Although the reported measurements of the elastic electron cross section are generally consistent, there are some disagreements at higher energies; more importantly, data below 6 eV collision energy are scant, with the only reported measurements being those of Allan [15].…”