Products and Reaction Sequences in Tetrahydrofuran Exposed to Low-Energy Electrons

Absolute cross sections for electronic excitation of condensed tetrahydrofuran (THF) by 11-16 eV electrons

Absolute cross section (CS) data on the interaction of low energy electrons with DNA and its molecular constituents are required as input parameters in Monte-Carlo type simulations, for several radiobiological applications. Previously [V. Lemelin et al., J. Chem. Phys. 144, 074701 (2016)], we measured absolute vibrational CSs for low-energy electron scattering from condensed tetrahydrofuran, a convenient surrogate for the deoxyribose. Here we report absolute electronic CSs for energy losses of between 6 and 11.5 eV, by electrons with energies between 11 and 16 eV. The variation of these CSs with incident electron energy shows no evidence of transient anion states, consistent with theoretical and other experimental results, indicating that initial electron capture leading to DNA strand breaks occurs primarily on DNA bases or the phosphate group.

Absolute vibrational cross sections for 1-19 eV electron scattering from condensed tetrahydrofuran (THF)

Absolute cross sections (CSs) for vibrational excitation by 1-19 eV electrons impacting on condensed tetrahydrofuran (THF) were measured with a high-resolution electron energy loss spectrometer. Experiments were performed under ultra-high vacuum (3 × 10(-11) Torr) at a temperature of about 20 K. The magnitudes of the vibrational CSs lie within the 10(-17) cm(2) range. Features observed near 4.5, 9.5, and 12.5 eV in the incident energy dependence of the CSs were compared to the results of theoretical calculations and other experiments on gas and solid-phase THF. These three resonances are attributed to the formation of shape or core-excited shape resonances. Another maximum observed around 2.5 eV is not found in the calculations but has been observed in gas-phase studies; it is attributed to the formation of a shape resonance.

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

Dissociative electron attachment (DEA) to diethyl ether yielded primarily the C(2)H(5)O(-) 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(-) 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(-) and C(4)H(7)O(-) 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(-) 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(-) ion cool enough to be observed. The CH(2)(CH(2))(3)O(-) 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.