Absolute cross sections for elastic electron scattering from methylformamide

Elastic electron scattering from gaseous methylformamide ($N$-methylformamide, C${}_2$H${}_5$NO) has been investigated. Absolute elastic differential cross sections (DCSs) were determined both experimentally and theoretically for the incident energies from 50 to 300 eV. The measurements were performed using a cross-beam technique, for scattering angles from 20° to 110°. Relative elastic DCSs were measured as a function of both the angle and the incident energy and the absolute DCSs were determined using the relative flow method. The calculations of electron interaction cross sections are based on a corrected form of the independent-atom method, known as the SCAR (screen corrected additivity rule) procedure and using an improved quasifree absorption model. Calculated integral cross sections have been presented, as well, both for methylformamide and formamide, in the energy range 10–1000 eV, and discussed. The results are compared with and discussed regarding existing data for other small molecules representing building blocks of large biomolecules.

Figure 1

Schematic drawing of formamide (CH${}_3$NO), trans-$N$-methylformamide (C${}_2$H${}_5$NO) and peptide bond linking two amino acids.

Figure 2

Angular dependence of absolute differential cross sections for elastic electron scattering from $N$-methylformamide at different incident energies. Circles represent the final absolute experimental differential cross sections, stars represent absolute values obtained by relative flow measurements; the calculations are presented by the solid line.

Figure 3

Angular dependence of absolute differential cross sections for elastic electron scattering from formamide and $N$-methylformamide (NMF) at the incident energies of 100 and 300 eV. The experimental results are presented by circles (NMF) and pentagons (formamide, [15]). The theoretical results are presented by solid line (NMF) and dashed line (formamide, [15]). The inset shows a comparison of the difference between absolute DCSs for NMF and formamide (squares, DCS${}_{\mathrm{NMF}}$–DCS${}_{\mathrm{formamide}}$) with the most recent experimental results for methane (triangles, CH${}_4$) published by Cho et al. [29] (100 eV) and Iga et al. [30] (300 eV).

Figure 4

Energy dependence of absolute differential cross sections for elastic electron scattering from $N$-methylformamide (NMF) and formamide at the scattering angle of 40°. (Stars) experimental points for NMF extracted from the present tabulated absolute DCSs; (circles) direct independent measurement for NMF as a function of the incident energy, normalized at 150 eV; (pentagons) experimental points for formamide extracted from published tabulated absolute DCSs [15]; (solid line) theory for NMF; (dashed line) theory for formamide.

Figure 5

Calculated total cross section (dash-dot), integral electronically inelastic cross section (dash-dot-dot), and integral elastic cross section (solid line) for electron scattering from NMF molecule. The integral elastic cross section for electron scattering from formamide molecule calculated by the present method (long dash) and previously calculated in the static-exchange-polarization approximation by Bettega [16] (short dash) are presented as well.