Electron collisions with ammonia and formamide in the low- and intermediate-energy ranges

Abstract

We report an investigation on electron collisions with two nitrogen-containing compounds, namely ammonia (${\mathrm{NH}}_{3}$) and formamide (${\mathrm{NH}}_{2}\mathrm{CHO}$). For ammonia, both theoretical and experimental differential, integral, and momentum-transfer cross sections, as well as calculated grand-total and total absorption cross sections, are reported in the 50--500 eV incident energy range. Calculated results of various cross sections are also reported for energies below 50 eV. Experimentally, angular distributions of the scattered electrons were measured using a crossed electron beam-molecular beam geometry and then converted to absolute differential cross sections using the relative flow technique. Absolute integral and momentum-transfer cross sections for elastic ${e}^{\ensuremath{-}}$-ammonia scattering were also derived from the measured differential cross sections. For formamide, only theoretical cross sections are presented in the 1--500 eV incident energy range. A single-center-expansion technique combined with the method of Pad\'e was used in our calculations. For both targets, our calculated cross sections are compared with the present measured data and with the theoretical and experimental data available in the literature and show generally good agreement. Moreover, for formamide, two shape resonances located at 3.5 eV and 15 eV which correspond to the continuum ${}^{2}{A}^{\ensuremath{'}\ensuremath{'}}$ and ${}^{2}{A}^{\ensuremath{'}}$ scattering symmetries, respectively, are identified. The former can be associated to the ${}^{2}{B}_{1}$ shape resonance in formaldehyde located at around 2.5 eV, whereas the latter can be related to the ${}^{2}E$ resonance in ammonia at about 10 eV. Such correspondence is very interesting and so supports the investigation on electron interaction with small building blocks, instead of with larger biomolecules.