Differential and integral cross sections for elastic electron collisions with uracil, cytosine, guanine, adenine and thymine have been calculated using the independent atom method with a static-polarization model potential for incident energies ranging from 50 to 4000 eV. Total cross sections for single electron-impact ionization of selected DNA and RNA bases have also been calculated with the binary-encounter-Bethe model from the ionization threshold up to 5000 eV. Cross sections within the investigated energy range, can be related to the molecular symmetry, the number of target electrons and molecular size; elastic and ionization processes are most efficient for guanine and adenine molecules, while the lowest cross sections were obtained for the uracil molecule. The ionization cross sections for cytosine, thymine, adenine and guanine are compared with those recently obtained with a semi-classical and binary-encounter-Bethe formalisms. No theoretical and experimental data for elastic electron scattering from DNA and RNA bases are available, but comparisons with calculations for molecules of similar size and geometry allows the validity of the theoretical approach to be verified.

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The absolute total cross section ͑TCS͒ for electron collisions with tetrahydrofuran C 4 H 8 O in the gas phase has been measured using the linear transmission technique within 1 -370 eV energy range. The total cross section function for e − -C 4 H 8 O collisions is characterized by the relatively high magnitude and the broad enhancement spanned between 4 and 12 eV, with some resonantlike structures. This enhancement can be explained as a result of overlapping core-excited resonances. At higher collision energies the magnitude of the measured total cross section monotonically decreases with the energy increase. At low impact energies some additional weak resonant features are visible near 1.9 and 3.5 eV. The reported TCS results are higher by 30% than recently published by Zecca et al. ͓J. Phys. B 38, 2079 ͑1995͔͒. They are also distinctly different from the recent R-matrix calculations. At intermediate energy range the present data agree well with the sum of calculated elastic and ionization cross sections.

Total dissociative electron attachment cross sections are presented for the amino acids, glycine, alanine, proline, phenylalanine, and tryptophan, at energies below the first ionization energy. Cross section magnitudes were determined by observation of positive ion production and normalization to ionization cross sections calculated using the binary-encounter-Bethe method. The prominent 1.2 eV feature in the cross sections of the amino acids and the closely related HCOOH molecule is widely attributed to the attachment into the -COOH * orbital. The authors discuss evidence that direct attachment to the lowest * orbital may instead be responsible. A close correlation between the energies of the core-excited anion states of glycine, alanine, and proline and the ionization energies of the neutral molecules is found. A prominent feature in the total dissociative electron attachment cross section of these compounds is absent in previous studies using mass analysis, suggesting that the missing fragment is energetic H − .

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We report cross-section results from experimental and theoretical studies on electron collisions with 1-butyne (HC≡C-CH 2 CH 3 ) and acetylene (HC≡CH) molecules and from computations for a propyne (HC≡C-CH 3 ) molecule. Absolute grand -total electron-scattering cross sections (TCSs) were measured at impact energies ranging from about 0.5 to 300 eV using the linear electron-transmission method. The TCS energy curve for 1-butyne has a very broad enhancement on which some distinct features are superimposed, namely a resonant-like maximum (located near 3.2 eV), a broad hump (centered around 7.5 eV), and a shoulder (spanned between 12 and 26 eV). The shape of our experimental TCS curve for acetylene closely resembles that reported earlier, while its magnitude is usually larger. As no previous calculations for electron collisions with 1-butyne and propyne are disclosed in the literature, we computed the elastic (ECS) and ionization (ICS) cross sections for these molecules. Similar calculations were also performed for acetylene molecules. The additivity rule was employed to calculate the ECSs from 50 to 3000 eV, while the binary-encounter-Bethe approach was used for computation of the ICSs, from the threshold up to 3000 eV. The sum (ECS + ICS) of these two computed cross sections reasonably reproduces the TCS measurements above 50 eV. Furthermore, the experimental TCS curves, obtained in our laboratory, for a series of acetylenic compounds-acetylene (HC≡CH), propyne (HC≡C-CH 3 ), and 1-butyne (HC≡C-CH 2 CH 3 )-are compared to study the substitutional effect. Finally, the influence of the structural differences on the electron-scattering TCS for isomers of the C 4 H 6 molecule (1-butyne, 2-butyne, and 1,3-butadiene) is indicated and discussed.

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