Averaged electron collision cross sections for thermal mixtures of $\alpha$-Alanine conformers in the gas phase

TL;DR

This study calculates electron collision cross sections for nine conformers of gas-phase $ ext{α}$-alanine, considering their populations and resonance features, providing averaged data relevant for understanding electron interactions with this amino acid.

Contribution

It presents the first detailed theoretical calculation of electron collision cross sections for individual conformers of $ ext{α}$-alanine and their thermal averages, including resonance features and population effects.

Findings

Resonance positions vary from 2.6 eV to 3.1 eV.

Thermally-averaged cross sections agree with experimental data.

Conformers IIA and IIB significantly influence the average due to large dipole moments.

Abstract

A theoretical study of elastic electron collisions with 9 conformers of the gas-phase amino acid $\alpha$-alanine (CH$_3$CH(NH$_2$)COOH) is performed. The eigenphase sums, resonance features, differential and integral cross sections are computed for each individual conformer. Resonance positions for the low-energy $\pi^*$ shape resonance are found to vary from 2.6 eV to 3.1 eV and the resonance widths from 0.3 eV to 0.5 eV. Averaged cross sections for thermal mixtures of the 9 conformers are presented. Both theoretical and experimental population ratios are considered. Thermally-averaged cross sections obtained using the best theoretical estimates give reasonable agreement with the observed thermal cross sections. Excited conformers IIA and IIB make a large contribution to this average due to their large permanent dipole moments.