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The well-known spherical complex optical potential (SCOP) and complex scattering potential-ionization contribution (CSP-ic) methods with appropriate modifications are applied to the CHX (X = F, Cl, Br, and I) molecules to compute positron scattering cross sections, which rather is the first theoretical attempt to report the same. Besides, various inelastic cross sections are also predicted for the first time in this Article. We have utilized the multiscattering spherical complex optical potential (MSCOP) approach to derive these cross sections. In general, a reasonable accordance has been found between the present total cross sections and the experimental measurements. Apart from the inconsistency between the present theoretical and previous experimental cross sections in the low energy region, the present theory is found to produce consistent and reliable results at all other energies.

Two independent methods, namely, Binary-encounter Bethe (BEB) and complex scattering potential-ionization contribution (CSP-ic) methods, are employed to calculate the total ionization cross section (Qion) for cyclic organic molecules from ionization threshold to 5 keV for which there is a paucity of data in the literature. The Qion calculated with the (BEB/ωB97X) combination is found to give good agreement with the experimental results, the CSP-ic method, and the Qion calculated from Irikura orbital energies. The Qion for most of the targets are calculated for the first time over such a wide energy range. Hence, to check the consistency and reliability of the present data, we have also computed the static polarizability for all the targets and the variation of maximum ionization cross section (Qion,max) with polarizability is studied. A linear relationship is observed between these quantities indicating the consistency and reliability of the present Qion data. The targets studied are important for industrial applications, radiation biology, and astrophysics.

Investigation of the valence state photoionization of water using vacuum ultraviolet and soft x-rays gives important information for spectroscopic analysis and studies of radiation loss and cell biology. In this article, the total and valence-shell photoionization cross sections of H2O and D2O, generating the states 2B1, 2A1 and 2B2, and their isotopic consequences are studied. The effect of bonding on valence state photoionization is also reported. The calculations were made using R-matrix theory for photon energies up to 40 eV. Electronic transitions below 20 eV were considered to account for the autoionizing Rydberg transitions. This is the first report to demonstrate the effect of bonding on valence state photoionization. For the isotopic partner (D2O), we observed a quantitative change in cross section. Comparisons are made with the previously available results and a reasonable agreement is found. The present study gives a comprehensive understanding of the photoionization of water, thus providing deep insight into different non-dissociative processes of the molecule in various environments.

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