Positron and electron collisions with formaldehyde (Vol. 42, No. 6)

New interest in electron and positron scattering from atoms and molecules has grown in the last few years. Understanding the fundamental forces, like the Coulomb and the dipole interaction, driving the collisional processes between the incident particle and the target, both experimentally and in the development of scattering theory, is a crucial topics in physics.

Formaldehyde (CH₂O) is a relatively small and simple fundamental organic species, from which many chemical compounds are derived. In addition, this molecule is characterised by a strong dipolar nature, a property which is expected to play a significant role in affecting the probability of very low-energy scattering. Despite these interesting properties, it had attracted only very little attention so far. The very first absolute cross sections for low energy positron and electron scattering from formaldehyde are reported here, hereby filling in a gap in the available knowledge on this key species.

Experimental total cross sections and calculated elastic integral cross sections for positrons in the energy range ~0.25-50 eV, together with theoretical results of electron total cross sections are presented. As can be seen from the results shown in the figure, the very large slope and magnitude of the low-energy cross sections reflect well the largely polar nature of formaldehyde. As a result of this work, formaldehyde can be used as an excellent candidate species against which further advances in scattering theory might be benchmarked.