An R-matrix study of singlet and triplet continuum states of N₂

Abstract

A systematic calculation of the positions and widths of the resonances converging on the first two excited states of N + 2 (A 2 u and B 2 + u ) is presented. A closely-spaced grid of geometries is used to give continuous resonance curves without the need for curve fitting. Three methods, fitting the eigenphase sum, the time-delay method and the R-matrix specific QB method, are tested. Fits to the longest three time-delays are found to give the most reliable and complete determination of the resonance parameters. The low excitation energies of the A and B ion states results in complex resonance features with many avoided crossings leading to pronounced structures in both the resonance curves and the associated widths. The resonance curves likely to be important for dissociative recombination are identified. Their positions generally agree well with the calculations of Guberman, although in some cases their widths are narrower. Full data on all curves is provided.

Rotational transitions induced by collisions ofHD+ions with low-energy electrons

“…A further step in the same direction will be the use of more accurate molecular data. This will be achieved by using the latest and ongoing progress in the R-matrix and MQDT techniques [47,54,55] in producing potential energy curves and electronic couplings, which can be used to produce realistic models (positions, amplitudes, and widths) for the Rydberg resonances dominating the shape of the cross sections. An alternative route to improved accuracy is the use of the global version of the MQDT [56], which has proved its efficiency in the spectroscopy of the neutral H 2 and its isotopes [57].…”

Dissociative recombination ofN2+: Anab initiostudy

“…The data to form the potential-energy curves are taken from an R-matrix study using the UKRmol code suite [25], henceforth referred to as I [19] and II [20], respectively. The R-matrix method is a sophisticated quantum mechanical scattering technique and can be used to calculate bound and resonant (quasibound) electronic states of a molecule.…”

“…For ionic targets the R-matrix method matches asymptotically to Coulomb functions; further details of the method can be found in the review by one of us [21]. Bound states were calculated by solving for negative scattering energies using the module BOUND [19,25,26] and resonant states we found using the time-delay method with an improved fitting technique for overlapping resonances [20,27,28]. The calculations of the bound and resonant states are described extensively in I and II, respectively.…”

“…Guberman [14][15][16][17][18] has performed a series of calculations on the DR of N + 2 using high-quality curves and couplings computed using standard quantum chemistry procedures and a multichannel quantum defect theory (MQDT) treatment of the actual DR process. Recently, two of us obtained comprehensive bound [19] and resonance [20] curves ab initio using the R-matrix method [21]. Previous studies using R-matrix curves for DR calculations [22][23][24] have obtained excellent results.…”

A parallel algorithm for Hamiltonian matrix construction in electron–molecule collision calculations: MPI-SCATCI

“…His algorithm, as implemented in module SCATCI and which is discussed in detail below, has formed the backbone of various implementations of the UK Molecular R-matrix codes [9][10][11][12][13]. The algorithm used by SCATCI is extremely efficient leading it to be used for extensive close-coupling calculations on electron collisions N + 2 [14], SiN [15], CH 3 CN [16], uracil [17,18] pyramidine [19] and many others systems, as well as for studies of positron-molecule collisions [20][21][22].…”