Complex Scattering Potential-ionization Contribution Research Articles

Molecular processes for radiosensitizer compounds upon electron interactions

This work presents a theoretical analysis of electron impact elastic and inelastic processes for oxygen mimic and fluorinated radiosensitizer molecules over a wide energy range, spanning from ionization potential (IP) to 5 keV. The computation to determine elastic (Qel), inelastic cross sections (Qinel) and total cross sections (QT) is done through the Spherical Complex Optical Potential (SCOP) formalism and ionization cross sections (Qion) and summed excitation cross sections (∑Qexc) are deduced through the Complex Scattering Potential ionization contribution (CSP-ic) formalism. Additionally, a recently developed an alternative approach for complex and large molecules (55≤Z≤95), namely the Two Parameters Semiempirical Method (2p-SEM), for impact energy 50 eV to 5 keV is employed to estimate Qel and QT. These radiosensitizer molecules, imidazole, 2-nitroimidazole, 2-nitrofuran, 4(5)-nitroimidazole, pentafluorobenzoic acid, perfluorothiophenol are of particular interest due to their applications in cancer therapy treatment. Cross sections allow us to assess the probability of various molecular Processes occurring due to electron interaction. This work is the first report of the estimation of this electron driven molecular processes for these radiosensitizers except for imidazole and 2-Nitroimidazole where previous Qion results are available. Our Present results are in good accordance with available data from existing literature. The study incorporates various correlations to show size dependency of various cross sections and linear correlation of Qion vs. impact energy, Qel vs. impact energy, QT vs. impact energy and linear correlation of Qion (Max) vs. αI to confirm the credibility and consistency of the present results.

Theoretical investigation of electron interaction processes for furfural (C5H4O2) and p-benzoquinone (C6H4O2)

The present study aims to quantify the electron-induced inelastic and elastic processes for molecules of industrial relevance, furfural and p-benzoquinone. We have computed inelastic cross-sections (Qinel), elastic cross-sections (Qel) and total cross-sections (QT) through spherical complex optical potential (SCOP) formalism, from ionisation energy (IE) to 5000 eV. The continuum and discrete contributions of the Qinel have been calculated in terms of ionisation (Qion) and excitation (∑Qexc) cross-sections, respectively, by employing the complex scattering potential-ionisation contribution (CSP-iC) method. A novel 2-parameter semi-empirical method (2p-SEM), a useful approach applicable for the large molecules 55 < Z < 95 for calculating QT, has been proposed and validated. Computed results are compared with previous experimental and theoretical data. We have also estimated the dielectric constant (ε) using various methods and correlations with molecular ionisation for these applied molecules.

Electron- and positron-driven molecular processes for H2O, CO2, and NH3 in their gas and ice phases.

In this comprehensive study, we explored the molecular chemistry of H2O, CO2, and NH3 molecules in their gas and ice phases assisted by electron and positron interactions over a wide range of energy from threshold to 5000 eV. These simple molecules have immense applications in areas such as atmospheric sciences and astrochemistry. We employed the spherical complex optical potential (SCOP) model along with the complex scattering potential-ionization contribution (CSP-ic) model and modified them to quantify the probabilities of various charged particle-driven molecular processes through inelastic cross-sections (Qinel), total ionization cross-sections (Qion), direct ionization cross-sections (QD-ion), and positronium formation cross-sections (QPs) for these molecules in gas and ice phases. We propose a novel model that incorporates the band gap of a material for positron impact cross-sections with molecules in their condensed phase. This is the first study on electron interactions with NH3 (ice) and positron interactions with H2O, CO2, and NH3 in their condensed phase.

Positron scattering from structurally related biomolecules.

We report the integral elastic, momentum transfer, and inelastic (positronium formation and ionisation) cross sections for positron scattering from structurally related molecules. The molecules chosen for the current investigation are formamide, formylphosphine, formic acid, N-methylformamide, acetone, acetic acid, and formaldehyde. The cross sections were calculated using the optical potential approach and the complex scattering potential-ionisation contribution method for impact energies between 1 and 5 keV. A sizable repository of data is now available for positron scattering from various atoms and molecules; however, data on the impact of positrons on current targets is still scarce and fragmented. While most cross sections are the first of their kind, we analyze our total cross sections (TCSs) with the previous literature available, which has become attractive to researchers trying to model the tracks of charged particles in matter. TCSs have recently seen a resurgence in popularity thanks to their utility in specifying the mean-free path between the collisions of such simulations. We find good qualitative convergence between experimental and theoretical results below and above the positronium formation threshold. However, around the threshold region, a significant discrepancy is encountered, which can be accounted for due to the experiment's lack of forward angle scattering effect discrimination. This level of agreement evolves to become quantitative at intermediate and higher energies.

Theoretical investigations of positron collisions with phosphorus-containing compounds

A theoretical investigation of positron scattering from phosphorus-containing compounds (viz., PH3, P2H4, PCl3, PF3, PBr3, POF3, POCl3, and H2PO4) is reported in this article. The quantum mechanical potential scattering approach is utilized to calculate integral elastic, excitation, momentum transfer, direct ionization, positronium formation, total ionization, inelastic, differential, and total cross sections on a fine energy grid from 1 to 5000 eV. The ionization contribution in the inelastic scattering is estimated using the complex scattering potential-ionization contribution technique. Prior research on positron collisions with these targets is scarce; as a result, the purpose of this study is to make up, at least in part, for this deficiency in cross-section data. In addition to being pertinent to positron transport analyses, such as Monte Carlo methods, the current results should be useful to benchmark the accuracy and validity of positron molecule collision computations and, more significantly, to compare these calculations with related electron scattering outcomes. Furthermore, the calculated cross sections of PH3 are compared with NH3 and other phosphorus-containing compounds. The analysis makes it abundantly evident that the atoms on the periphery of a molecule have a substantially larger impact on the scattering process than the central atom. To analyze the scattering dynamics of positrons and their anti-particle electrons, a comparative study of cross sections of H2PO4 and H2SO4 is also presented. For most of these targets, positron calculations are carried out for the first time.

Electron driven molecular processes for nucleosides

In the present study we investigate electron interactions with important cell molecules, nucleosides viz. Adenosine, Guanosine, Cytidine, Thymidine and Uridine from ionisation energy to 5000 eV. While nucleobases are studied extensively, these nucleosides have not been investigated enough. We focus to quantify various molecular processes induced by electrons through inelastic (Qinel), ionisation (Qion), electronic excitations (Qexc), elastic (Qel) and total (Qtotal) cross-sections. We used the complex optical potential approach to compute inelastic and elastic probabilities and employed complex scattering potential-ionisation contribution method to perform the calculations to bifurcate inelastic processes in to discrete and continuum contribution. This work is the first report of all these quantities, except Qion, to investigate the electron induced local chemistry of these important DNA/RNA compounds.

Electron interactions with analogous of DNA/RNA nucleobases: 3-hydroxytetrahydroFuran and α-Tetrahydrofurfuryl alcohol

We report quantitative results for electron induced molecular processes for DNA/RNA nucleobase analogous bio-molecules, 3-hydroxytetrahydrofuran (C4H8O2, 3hTHF) and α-tetrahydrofurfuryl alcohol (C5H10O2, THFA), which are similar in structure and functional group to backbone of DNA and RNA. We have employed spherical complex optical potential (SCOP) formalism to compute total elastic (Qel) and inelastic (Qinel) cross sections and used Complex Scattering Potential-ionization contribution (CSP-ic) method to obtain total ionization (Qion) and summed total excitation (∑Qexc) cross sections. These results obtained for a wide energy range (10 eV - 5 keV) may serve as the input parameters in predicting damage in biomolecular systems induced by secondary electrons caused by primary ionization radiation. We have observed a correlation between maximum Qion and molecular polarizability volume (α), ionisation energy (IE) and number of valence electrons (Nv). This work includes an attempt to estimate ∑Qexc for these molecules in normal state.

Electron impact ionisation and other molecular processes for organoplatinum compounds

Electron interactions with platinum-based chemotherapeutic organoplatinum compounds, cisplatin (H6N2Cl2Pt), nedaplatin (C2H8N2O3Pt), carboplatin (C6H12N2O4Pt) and oxaliplatin (C8H14N2O4Pt), are studied for ionisation and other molecular processes from ionisation potential (IP) to 5 keV. Elastic cross sections Q el, inelastic cross sections Q inel and total cross sections Q T are computed using Spherical Complex Optical Potential (SCOP) formalism and ionisation cross-sections Q ion and summed excitation cross sections ∑Q exc are derived through Complex Scattering Potential – ionisation contribution (CSP-ic) method. Only theoretical data is available in the literature for these molecules and we find good accord with them. This is the first report of Q T, Q inel and Q exc for all these molecules and Q el for Nedaplatin.

Structural, spectroscopic and electron collisional studies of isoxazole (C3H3NO)

• Comprehensive structural, spectroscopic and electron collision data of Isoxazole. • DFT calculations of ground state geometry and vibrational frequencies. • Comparison with earlier data; confirmation/revision of vibronic assignments. • Vertical excitation energies for singlet and triplet states using TDDFT. • Low energy electron scattering data for Isoxazole from 0.1-20 eV. The structural, spectroscopic, and electron collision data of Isoxazole (C 3 H 3 NO) were subjected to extensive computational studies. Spectroscopic calculations were performed on ground and excited states using the density functional theory (DFT) and the time dependent density functional theory (TDDFT) respectively. Ground state geometry and vibrational frequencies agree well with earlier works and lead to re-assignment of a few vibrational bands. Theoretically predicted singlet and triplet excitation energies are in good agreement with earlier experimental data, while predicted oscillator strengths of singlet states correlate well with the observed relative spectral intensities. The electron collision data for isoxazole molecule were calculated using Quantemol-N, which employs the UK Molecular R-matrix codes. These calculations were performed for the total elastic cross-sections along with their symmetrical components, differential and momentum transfer cross-sections, inelastic scattering cross-sections comprising of discrete electronic excitation, ionization and dissociative electron attachment processes. We employed the two most popular theoretical approaches to calculate the electron impact ionization cross-sections viz. Complex scattering potential-ionization contribution (CSP-ic) and the Binary encounter Bethe (BEB) model. The rate coefficients for elastic and inelastic processes were estimated over a wide electron temperature range. In addition to scattering calculations, the other motivation was to obtain resonances which are signatures of many significant low energy phenomena. The first two peak correspond to π* shape resonances which are observed at 2.1 eV and 4.69 eV and are in accordance with the earlier reported data. The third peak is observed at 10.96 eV which may be attributed to the σ* shape resonance.

Electron induced elastic and inelastic processes for perfluoroketone (PFK) molecules

We report the results of calculations of elastic and inelastic (ionization and excitation) cross sections for electron scattering from perfluoroketone molecules, C x F2x O (x = 1–6) over a wide energy range, from ∼the ionization potential to 5 keV. These molecules have been determined to have extremely low global warming potentials and therefore may have applications in next generation gas discharges and plasma reactors. The results are derived using the complex scattering potential-ionization contribution method to investigate ionization cross sections Q ION and are found to be in good agreement with the available data. The spherical complex optical potential formalism is used to evaluate elastic (Q EL), inelastic (Q INEL) and total cross sections (Q T). This study is a maiden effort to report summed total excitation cross section (∑Q EXC), Q ION and Q INEL for CF2O and C2F4O, and Q EL and Q T for C x F2x O (x = 1–6). The study includes various correlation analyses and a prediction of the dipole polarizability.

Theoretical investigations of structural, spectroscopic and electron collision data of acetone

ABSTRACT Comprehensive computational studies are carried out for the structural, spectroscopic and electron collision data of acetone. The time-dependent density functional theory (TDDFT) is employed to compute singlet and triplet vertical excitation energies and to determine their valence/Rydberg character. Excellent correlation is obtained between the predicted spectral features with the available experimentally observed spectral features. We also report a detailed study on the e-acetone interactions for the comprehensive energy range starting from 0.1 to 5000 eV. We found a smooth matching of R-matrix and SCOP data for total cross sections at 17 eV and hence are able to estimate the total cross sections over such a wide energy range. Moreover, the study is augmented with additional data on Eigenphase sum, differential cross sections (DCS), momentum transfer cross sections (MTCS), electronic excitation cross-sections, symmetry decomposition of elastic cross sections, inelastic cross sections, etc. Ionisation cross-sections are computed using Complex scattering Potential-ionisation contribution (CSP-ic) and Binary Encounter Bethe (BEB) formalisms. Transport coefficients such as mean free path, diffusion and mobility coefficients are calculated from the effective collision frequency and the rate coefficients are estimated over a wide electron temperature range for elastic and inelastic processes. Importantly, we have been able to identify new resonances (; and ) from the present study. The theoretical data obtained here will be of great use in varieties of applications involving acetone.

Mean Free Paths and Cross Sections for Electron Scattering from Liquid Water.

Electron collision with liquid water is theoretically investigated and reported in this article. The range of projectile energy considered is 10-5000 eV, covering all major channels, viz., ionization, inelastic, elastic, and total scattering. The liquid phase electron charge density and static potential are generated and used in the calculation under a spherical complex optical potential formalism to achieve the goals. For the ionization channel, the complex scattering potential-ionization contribution method is used. The agreement with available theoretical data is satisfactory. The study on the total electron scattering from liquid water, using a common method for elastic and inelastic cross sections, is new and requires further attempts to support the reported data.

Double differential distributions of e-emission in ionization of N2 by 3, 4 and 5 keV electron impact

We report the measurement of the absolute double differential cross sections (DDCS) of secondary electrons emitted due to the ionization of N2 molecule in collisions with fast electrons having energies between 3 and 5 keV. The emitted electrons with energies from 1–500 eV have been measured for different forward and backward emission angles. The measured DDCS have been compared with the state-of-the-art first Born approximation with correct boundary condition (CB1) model calculations as well as with the classical trajectory Monte Carlo (CTMC) method. From the measured DDCS, the single differential cross sections (SDCS) as a function of the emission energies have been computed and eventually the total ionization cross sections (TCS) have been derived. The TCS values are also compared with a semi-empirical calculation, namely, the CSP-ic (complex scattering potential-ionization contribution) model.

Electron induced scattering cross section for pyrrole and its isomers

Elastic, ionization and total cross section for electron scattering from pyrrole and its isomers, viz. 2H-pyrrole, 3H-pyrrole, cycloprapanecarbonitrile, E-2 butenenitrile and Z-2 butenenitrile are reported in this article. These cross sections are calculated using the spherical complex optical potential formalism and the complex scattering potential-ionization contribution method in the energy range from the ionization threshold of the molecule to 5 keV. The geometric screening correction is used to reduce the overestimation of cross section due to overlap in charge distribution among atoms or group of atoms in the molecule. The isomeric effect through cross section values are also investigated in this work. The cross section data reported in this paper are key input for modeling Titan’s atmosphere due to the presence of pyrroles and abundant electrons in its medium.

Ionization cross sections for plasma relevant molecules

We have chosen five complex molecules (C3F6O, C4F8O, C5F10O, C6F12O and C4F7N) for the present investigation, which are considered as potential substitutes for SF6 in plasma applications. There are some theoretical data available for ionization cross sections with contradicting values, especially at the peak. To the best of our knowledge, no experimental data are found in the literature to validate previous calculations. In this work, we have efficiently included nuclear charge distribution and the corresponding electrostatic potential in the spherical complex optical potential formalism for the first time. Thus, the nuclear static effect is included in the calculation of inelastic cross section of these plasma relevant molecules by electron scattering. A complex scattering potential-ionization contribution method is used to derive the ionization cross section. We have done a test run of the adopted changes on targets for which experimental measurements are available. Excellent agreement can be found for the entire energy range. For present plasma relevant molecules, a notable difference is seen in the lower energy region of investigation, which is a major improvement in our calculation. However, beyond the peak, the values are consistent with previous methods. For C6F12O this is the first report of ionization cross section.

Positron Scattering from Pyridine and Pyrimidine.

Positron impact scattering cross-sections for pyridine and pyrimidine are reported here. Spherical complex optical potential formalism is used to calculate the positronium formation, elastic, total, and differential cross-sections. The ionization cross-sections calculated here are obtained employing the complex scattering potential-ionization contribution method. To account for the complex molecular structure of the target, an effective potential method is employed in our formalism for the first time. The contribution from rotational excitation is also included, which shows a reasonable comparison with the experimental data. The results obtained using the modified approach are encouraging and show very good agreement with the measurements. The differential cross-section for pyridine is reported for the first time.

Electron impact ionisation cross-sections for complex molecules

The main goal of this work is to compute the total ionisation cross-section for electron scattering from various complex molecules. The targets chosen are pyridazine, alanine, glycine, benzoic acid, phenylacetylene, ethylbenzene and n-propylbenzene. There is no previous literature available for these molecules except for pyridazine, alanine and glycine, and hence we present the first report of their ionisation cross-section. We apply the complex scattering potential-ionisation contribution (CSP-ic) method to compute the cross-sections from the respective ionisation threshold to 5000 eV. The result for the pyridazine molecule shows an excellent agreement with the available experimental data and binary encounter-Bethe (BEB) cross-sections. In the absence of any experimental comparison for other molecules, we have also calculated their BEB ionisation cross-sections. These two methods are well known for giving reasonable estimates of the ionisation cross-sections. The CSP-ic method is based on the molecular structure and properties, while the BEB method deals with molecular orbitals. Thus, comparing the two results will check the accuracy of these theoretical models and further increase the credibility of the reported cross-section. In general, fairly good agreement is observed between the two results. However, any inconsistencies observed are backed by valid reasons.

Electron impact total ionization cross sections of diboranes - B2H4 and B2H6

We report calculated total ionization cross sections of diborane molecules (B2H4 and B2H6) from threshold to ∼2 keV by two methods viz., Complex Scattering Potential-ionization contribution (CSP-ic) and Binary Encounter Bethe (BEB) formulations. In the CSP-ic method, total ionization cross sections Qion are extracted from total inelastic cross sections denoted by Qinel. In BEB, the Qion are obtained as the sum of molecular orbital cross sections. The results obtained through both methods are compared and are found to be in good mutual accord (except the atomic-sum estimate on B2H6), but both the theoretical results differ considerably from only available measurement on B2H6. There are no previous data for B2H4. Comparisons with corresponding hydrocarbon molecules are also afforded. Our work suggests fresh measurements on B2H6 and new experiments on B2H4.

Total ionization cross section of cyclic organic molecules.

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.

Electron interactions with astro chemical compounds

In present work electron induced processes with important astro-compounds found in the tholins of Titan are investigated. We report calculated total elastic cross sections Qel, total inelastic cross sections Qinel, total ionization cross sections Qion, total excitation cross sections ∑Qexc and total cross sections QT for hydrogen cyanide (HCN), cyanoacetylene (HCCCN), vinyl cyanide (CH2CHCN), methanimine (CH2NH) and ethanimine (CH3CHNH) on electron impact for energies from ionization threshold to 5 keV. We have employed the Spherical Complex Optical Potential (SCOP) formalism to investigate elastic as well as inelastic processes and used Complex Scattering Potential – ionization contribution (CSP-ic) method to derive ionization cross sections. In absence of any theoretical or experimental data of ionization cross sections except for HCN and HCCCN, we have computed Qion using the Binary- Encounter- Bethe (BEB) method for all these molecules and have found reasonable agreement. This is the maiden attempt to report various total cross sections for all these astro-molecules except HCN and HCCCN.