Cross Sections and Asymmetry Parameters for Formic Acid in the Vacuum-Ultraviolet Energy Range

Abstract

We present an experimental and theoretical investigation of the photon interaction with formic acid in the vacuumultraviolet energy range. The absolute absorption cross sections and ionization efficiencies were measured in the 11.2−21.4 and 13.5−21.4 eV ranges, respectively, using a double-ion chamber technique. Photoionization and neutral-decay cross sections were derived from these results. From the present ionization cross sections and previously reported ionic dissociative branching ratios, the partial cross sections for dissociating processes were obtained. Theoretically, the photoionization cross sections and the asymmetry parameters of the photoelectron angular distributions for ionization out of the six outermost valence orbitals (10a′, 2a″, 9a′, 1a″, 8a′, and 7a′) were obtained in the energy range from near-threshold to 35 eV. For that, the Padéapproximant technique along with the single-center partial-wave expansion method was applied to solve the Lippmann-Schwinger equation in the static-exchangepolarization level of approximation. This is the first theoretical investigation concerning the determination of the asymmetry parameters and photoionization cross sections of formic acid in the vacuum-ultraviolet energy range. Comparison is made between our results and the previous ones.

A polarization-consistent R-matrix model: application to the photoionization of molecules

“…Although the experimental data only covers the lower energy region i.e., below 23 eV, it appears as though both crosssections exhibit a plateau starting around 18 eV. This plateau is also observed in the experimental data of Fujimoto et al (2020) albeit with a slightly larger cross-section. The PC-CHF(N) model also shows a plateau-like structure at the same energy but with a significantly smaller cross-section.…”

“…Figure 10 compares the state-resolved R-matrix photoionization cross-sections and asymmetry parameters with the ePolyScat-D calculations of Fujimoto et al (2020). In general, for the first 6 ionic states, we can see close agreement between the SE calculation using the R-matrix method and the calculation from Fujimoto et al (2020). This is to be expected as both calculations contain only a single elastic channel.…”

“…The PC-CHF(N) model also shows a plateau-like structure at the same energy but with a significantly smaller cross-section. In the calculations of Fujimoto et al (2020) the plateau is not observed, instead the cross-section peaks around 17 eV and then falls off as the photon energy increases. The ePolyScat-D data of Fujimoto et al (2020) is based on a single-active electron model which omits state-coupling and hence models elastic collisions only.…”

“…This makes it an ideal candidate to study biomolecules such as amino acids and DNA base pairs (Tenorio et al 2019). In this work we will only focus on the monomer for which prior theoretical and experimental data are available (Leach et al 2002, Fujimoto et al 2020.…”

“…The smoothed (black solid) and raw (light grey) results of the PC-CHF(N) model are compared with SE (red dashed) calculations, the CC (blue dot-dash) calculations of Benda et al (2022) and the experimental data of Brion and Tan (1979) (red triangle), Carlson et al (1983) (orange circle) and Truesdale et al (1983) (green bar). obtained using the PC-CHF(N) and CC R-matrix models with the ePolyScat-D calculations of Fujimoto et al (2020) and experimental data of Fujimoto et al (2020), Leach et al (2002) and Schwell et al (2002). The photoionization cross-section data is a combination of the photoabsorption cross-section measured by Leach et al (2002) and the quantum efficiency measured by Schwell et al (2002).…”