Bobby Antony

The Virtual Atomic and Molecular Data Centre (VAMDC) Consortium

The Virtual Atomic and Molecular Data Centre (VAMDC) Consortium is a worldwide consortium which federates atomic and molecular databases through an e-science infrastructure and an organisation to support this activity. About 90% of the inter-connected databases handle data that are used for the interpretation of astronomical spectra and for modelling in many fields of astrophysics. Recently the VAMDC Consortium has connected databases from the radiation damage and the plasma communities, as well as promoting the publication of data from Indian institutes. This paper describes how the VAMDC Consortium is organised for the optimal distribution of atomic and molecular data for scientific research. It is noted that the VAMDC Consortium strongly advocates that authors of research papers using data cite the original experimental and theoretical papers as well as the relevant databases.

Calculations of elastic, ionization and total cross sections for inert gases upon electron impact: threshold to 2 keV

In this paper we report comprehensive calculations of total elastic (Qel), total ionization (Qion) and total (complete) cross sections (QT) for the impact of electrons on inert gases (He, Ne, Ar, Kr and Xe) at energies from about threshold to 2000 eV. We have employed the spherical complex optical potential (SCOP) formalism to evaluate Qel and QT and used the complex spherical potential-ionization contribution (CSP-ic) method to derive Qion. The dependence of QT on polarizability and incident energy is presented for these targets through an analytical formula. Mutual comparison of various cross sections is provided to show their relative contribution to the total cross sections QT. Comparison of QT for all these targets is carried out to present a general theoretical picture of collision processes. The present calculations also provide information, hitherto sparse, on the excitation processes of these atomic targets. These results are compared with available experimental and other theoretical data and overall good agreement is observed.

Electron impact ionization cross-section of C2, C3, Si2, Si3, SiC, SiC2 and Si2C

Total ionization cross-sections for C2, C3, Si2, Si3, SiC, SiC2 and Si2C molecules have been calculated by electron impact. Spherical complex optical potential formalism has been employed for obtaining the inelastic cross-sections for these molecules. Then by applying complex scattering potential-ionization contribution method, total ionization cross-sections are derived. These cross-sections are calculated in the energy range from ionization threshold to 2 keV. There are no measurements available in the literature to the best of our knowledge with which our results can be compared. The results show a linear relationship between maximum ionization cross-section and square root of the ratio of polarizability to ionization potential, depending on its atomicity. This gives a confirmation for the consistency of the data reported here. Present work is a maiden attempt to find electron impact ionization cross-section for these molecules, except for C2 and C3.

Total and ionization cross sections of electron scattering by fluorocarbons

Electron impact total cross sections (50–2000 eV) and total ionization cross sections (threshold to 2000 eV) are calculated for typical plasma etching molecules CF4, C2F4, C2F6, C3F8 and CF3I and the CFx (x = 1–3) radicals. The total elastic and inelastic cross sections are determined in the spherical complex potential formalism. The sum of the two gives the total cross section and the total inelastic cross section is used to calculate the total ionization cross sections. The present total and ionization cross sections are found to be consistent with other theories and experimental measurements, where they exist. Our total cross section results for CFx (x = 1–3) radicals presented here are first estimates on these species.

Electron impact total ionization cross sections for atoms with Z = 49-54

Spherical complex optical potential formalism and complex scattering potential–ionization contribution are used to generate electron impact total inelastic and total ionization cross section, respectively, for the atoms In, Sn, Sb, Te, I and Xe. Roothaan–Hartree–Fock calculations are used to approximate the atomic orbital wavefunction and hence to model the target charge densities and static potentials for these atoms. The results for the above targets are presented for energies ranging from ionization threshold to 2000 eV. Graphs are plotted with other theories and measurements wherever available. We have obtained a systematic and uniform result with an overall agreement with other data for all the elements presented here.

Electron impact ionization of cycloalkanes, aldehydes, and ketones

The theoretical calculations of electron impact total ionization cross section for cycloalkane, aldehyde, and ketone group molecules are undertaken from ionization threshold to 2 keV. The present calculations are based on the spherical complex optical potential formalism and complex scattering potential ionization contribution method. The results of most of the targets studied compare fairly well with the recent measurements, wherever available and the cross sections for many targets are predicted for the first time. The correlation between the peak of ionization cross sections with number of target electrons and target parameters is also reported. It was found that the cross sections at their maximum depend linearly with the number of target electrons and with other target parameters, confirming the consistency of the values reported here.

Electron impact total cross section for acetylene over an extensive range of impact energies (1 eV-5000 eV)

Comprehensive study on electron impact for acetylene molecule is performed in terms of eigenphase diagram, electronic excitation cross sections as well as total cross section calculations from 1 eV to 5000 eV in this article. Computation of cross section over such a wide range of energy is reported for the first time. We have employed two distinct formalisms to derive cross sections in these impact energies. From 1 eV to ionization threshold of the target we have used the ab initio R-matrix method and then spherical complex optical potential method beyond that. At the crossing point of energy, both theories matched quite well and hence prove that they are consistent with each other. The results presented here expectedly give excellent agreement with other experimental values and theories available. The techniques employed here are well established and can be used to predict cross sections for other targets where data are scarce or not available. Also, this methodology may be integrated to online database such as Virtual Atomic and Molecular Data Centre to provide cross section data required by any user.

Screening-corrected electron impact total and ionization cross sections for boron trifluoride (BF3) and boron trichloride (BCl3)

In this paper, we report modified calculations for total elastic, total ionization and total (complete) cross sections for boron trifluoride (BF3) and boron trichloride (BCl3) upon electron impact at energies from around threshold to 2000 eV. We have proposed a model which allows screening correction due to the overlapping of atoms as seen by incident electrons in a complex molecule. We have employed the well-known spherical complex optical potential (SCOP) formalism to evaluate total elastic and total inelastic cross sections and hence total (complete) cross sections. The ionization cross sections were derived using the complex optical potential–ionization contribution (CSP-ic) method developed by us. The present results are compared with available experimental and other theoretical data wherever available and overall good agreement is observed. The present screening-corrected model shows improvement over the previous method especially at low energies. We also predict total elastic cross sections for these targets using this method.

Calculation of total and ionization cross sections for electron scattering by primary benzene compounds

The total and ionization cross sections for electron scattering by benzene, halobenzenes, toluene, aniline, and phenol are reported over a wide energy domain. The multi-scattering centre spherical complex optical potential method has been employed to find the total elastic and inelastic cross sections. The total ionization cross section is estimated from total inelastic cross section using the complex scattering potential-ionization contribution method. In the present article, the first theoretical calculations for electron impact total and ionization cross section have been performed for most of the targets having numerous practical applications. A reasonable agreement is obtained compared to existing experimental observations for all the targets reported here, especially for the total cross section.

Theoretical Formalism To Estimate the Positron Scattering Cross Section

A theoretical formalism is introduced in this article to calculate the total cross sections for positron scattering. This method incorporates positron-target interaction in the spherical complex optical potential formalism. The study of positron collision has been quite subtle until now. However, recently, it has emerged as an interesting area due to its role in atomic and molecular structure physics, astrophysics, and medicine. With the present method, the total cross sections for simple atoms C, N, and O and their diatomic molecules C2, N2, and O2 are obtained and compared with existing data. The total cross section obtained in the present work gives a more consistent shape and magnitude than existing theories. The characteristic dip below 10 eV is identified due to the positronium formation. The deviation of the present cross section with measurements at energies below 10 eV is attributed to the neglect of forward angle-discrimination effects in experiments, the inefficiency of additivity rule for molecules, empirical treatment of positronium formation, and the neglect of annihilation reactions. In spite of these deficiencies, the present results show consistent behavior and reasonable agreement with previous data, wherever available. Besides, this is the first computational model to report positron scattering cross sections over the energy range from 1 to 5000 eV.