Hemal N. Varambhia

Quantemol-N: an expert system for performing electron molecule collision calculations using the R-matrix method

The R-matrix method has been widely employed to ab initio calculations on a large variety of problems related to electron molecule scattering. The UK Molecular R-matrix Code, which are a synthesis between codes designed for quantum chemistry and electron atom scattering calculations, has proved particularly popular for these studies but is difficult for the non-specialist to use. The Quantemol-N software environment is designed for scientists with a minimal knowledge of scattering theory or quantum chemistry to use without the need of a complex and dedicated training. Their use is illustrated for low energy electron collisions with silane.

Electron-impact rotational and hyperfine excitation of HCN, HNC, DCN and DNC

Rotational excitation of isotopologues of HCN and HNC by thermal electron-impact is studied using the molecular R-matrix method combined with the adiabatic-nuclei-rotation approximation. Rate coefficients are obtained for electron temperatures in the range 5–6000 K and for transitions among all levels up to J= 8 . Hyperfine rates are also derived using the infinite-order-sudden scaling method. It is shown that the dominant rotational transitions are dipole-allowed, that is, those for which ΔJ= 1 . The hyperfine propensity rule ΔJ=ΔF is found to be stronger than that in the case of He–HCN collisions. For dipole-allowed transitions, electron-impact rates are shown to exceed those for excitation of HCN by He atoms by six orders of magnitude. As a result, the present rates should be included in any detailed population model of isotopologues of HCN and HNC in sources where the electron fraction is larger than 10−6, for example, in interstellar shocks and comets.

Electron collision with the silicon monoxide (SiO) molecule using the R-matrix method

SiO is a molecule that is well known astrophysically. Electron scattering calculations are presented at the static-exchange and close-coupling approximations, one including 24 target states and another including 48 states. Our study predicts the existence of several low-lying narrow 2Π, 2Δ and 2Σ− Feshbach resonances and confirms the existence of a 2Π bound state. Results from the 48-state close-coupling calculation have been employed to calculate rotational (de)excitation rates and rate-fitting coefficients, which are useful in astrophysical modelling. Ionization cross sections, rotationally summed and resolved differential and integral cross sections are also presented.

Electron collision with the HCN and HNC molecules using the R-matrix method

The linear isomers HCN and HNC are both well known astrophysically. Electron collision calculations are presented using a 24 target state close-coupling expansion and a variety of models. All of these confirm the presence of the previously identified 2Π HCN anion shape resonance, although it is found that this resonance is somewhat narrower than suggested by previous calculations. HNC is also predicted to have 2Π anion shape resonance at a similar energy but somewhat narrower than its HCN− counterpart. Furthermore HNC also supports two narrow Feshbach resonances of 2Σ+ and 2Δ symmetry. Results are presented for the electron impact electronic excitation of both molecules.