The R-matrix method is used to perform high-level calculations of electron collisions with beryllium mono-hydride at its equilibrium geometry with a particular emphasis on electron impact electronic excitation. Several target and scattering models are considered. The calculations were performed using (1) the UKRMol suite which relies on the use of Gaussian type orbitals (GTOs) to represent the continuum and (2) using the new UKRMol+ suite which allows the inclusion of B-spline type orbitals in the basis for the continuum. The final closecoupling scattering models used the UKRMol+ code and a frozen core, valence full configuration interaction, method based on a diffuse GTO atomic basis set. The calculated electronic properties of the molecule are in very good agreement with state-of-the-art electronic structure calculations. The use of the UKRMol+ suite proved critical since it allowed the use of a large R-matrix sphere (35Bohr), necessary to contain the diffuse electronic states of the molecule. The corresponding calculations using UKRMol are not possible due to numerical problems associated with the combination of GTO-only continuum and a large R-matrix sphere. This work provides the first demonstration of the utility and numerical stability of the new UKRMol+ code. The inelastic cross sections obtained here present a significant improvement over the results of earlier studies on BeH.

No abstract

A theoretical model for isotopologues of beryllium monohydride, BeH, BeD and BeT, A P 2 to X S + 2 visible and X S + 2 to X S + 2 infrared rovibronic spectra is presented. The MARVEL procedure is used to compute empirical rovibronic energy levels for BeH, BeD and BeT, using experimental transition data for the X S + 2 , A P 2 , and C S + 2 states. The energy levels from these calculations are then used in the program Duo to produce a potential energy curve for the ground state, X S 2 , and to fit an improved potential energy curve for the first excited state, A P 2 , including a spin-orbit coupling term, a Λ-doubling state to state (A-X states) coupling term, and Born-Oppenheimer breakdown terms for both curves. These, along with a previously computed ab initio dipole curve for the X and A states are used to generate vibrational-rotational wavefunctions, transition energies and A-values. From the transition energies and Einstein coefficients, accurate assigned synthetic spectra for BeH and its isotopologues are obtained at given rotational and vibrational temperatures. The BeH spectrum is compared with a high resolution hollow-cathode lamp spectrum and the BeD spectrum with high resolution spectra from JET giving effective vibrational and rotational temperatures. Full A-X and X-X line lists are given for BeH, BeD and BeT and provided as supplementary data on the ExoMol website.

Beryllium is being adopted for plasma facing walls in fusion reactors. This has led to the observation of emissions from the A 2 Π state of beryllium hydride. Use of these emissions to monitor Be erosion requires electron impact excitation rates. Cross sections for electron impact vibrational excitation within the X 2 Σ + state and vibrationally resolved electronic excitation to the A 2 Π state are reported for BeH, BeD and BeT. Electron collisions are studied at a range of internuclear separations using the UK molecular R-matrix (UKRmol+) codes. Electronic excitation is studied both within the Franck-Condon approximation and by explicit averaging of the T-matrix elements. It is found that (a) inclusion of the effect of higher partial waves using the Born approximation leads to significant increases in the cross sections and (b) the Franck-Condon approximation underestimates the importance of collisions for which the vibrational state changes during electronic excitation.

The UK molecular R-matrix codes are used to study electron collisions with the + He 2 molecular ion. Full configuration interaction calculations are performed to obtain the potential energy curves of the ground X S + u g u 3 3 3 3and D u 3 states, which are relevant for the study of the reactive collision of + He 2 with low-energy electrons. In addition, bound states are also calculated for each symmetry of He 2 at several geometries.