Low-energy positron collisions with water: elastic and rotationally inelastic scattering

Differential, integral and momentum transfer cross sections for the vibrationally elastic and rotationally inelastic scattering of positrons from water at low collision energy ( E <= 10 eV) are reported. Several models within the R-matrix method are used to compute the body-fixed T-matrices, while the scattering calculations are performed within the fixed-nuclei approximation corrected with the standard Born-closure formula. These calculations are compared with experimental results for elastic scattering, and the best model gives reasonable agreement with the most recent measurements (Zecca et al 2006 J. Phys. B: At. Mol. Opt. Phys. 39 1597) but not with some earlier studies. The relative contribution of the rotationally inelastic processes is investigated and comparisons are made with the equivalent electron scattering cross sections

R-matrix study for electron scattering of beryllium dihydride for fusion plasma

We report the integral elastic, differential, momentum transfer, dissociative electron attachment and electronic and rotational excitation cross sections for the lowenergy electron impact on beryllium dihydride (BeH2) computed using the QuantemolN interface for driving the UK molecular R-matrix code. The energy of the projectile electron is in the range 0.1-10 eV. The effect of multichannel coupling is investigated by calculating the cross sections with various target models by increasing the number of target states in the trial wavefunction of the entire scattering system. The cross sections converge for the calculation with more than 15-target states. The vertical excitation energies calculated with the present model give excellent agreement with the EOM-CCSD calculations. Collisional frequencies are determined using the momentum transfer cross section for a Maxwell-Boltzmann distribution. From the collisional frequency, the transport properties such as mean free path, diffusivity and mobility are calculated for the temperature range of 100 to 500000 K. The cross section data and transport properties reported in this article are important for fusion plasma

Studies of Elastic and Electronically Inelastic Electron-Molecule Collisions

Cross-sections for the scattering of low-energy electrons by molecules play an important role in the modeling of swarm and plasma etching systems, gas lasers, and planetary atmospheres. In contrast to the related atomic problem, the progress to date in both theoretical and experimental studies of electron-molecule scattering cross-sections has been limited [1]. On the theoretical side, this situation is primarily due to the additional complexities arising from the nonspherical potential fields of molecular targets. Most studies of electronic excitation of molecules by low-energy electrons have hence been carried out using low-order theories. These include plane-wave theories such as the Born Ochkur-Rudge approximations [2, 3], the impact-parameter method [4], and distorted-wave theories [5, 6]. Several studies of elastic scattering by molecules have also used local approximations to the nonlocal exchange potentials [7]. Although such theories and approximations can be computationally easy to apply, they do not contain enough of the collision physics to yield consistently reliable differential and integral cross sections, particularly at low and intermediate energies [8]. What is clearly needed are theoretical methods which can provide quantitatively reliable cross-sections for the elastic and inelastic scattering of low-energy electrons by molecules