Continuum and bound states of the e--CH+system using the R-matrix method

Molecular R-matrix calculations are performed on the astrophysically important e - -CH + system for internuclear separations in the range 1.5-4.0 a 0 . The calculations are performed for both 2 Pi and 2 Sigma total symmetries. Several approximations, the most sophisticated being a polarised three-state close-coupling expansion, are employed. Many resonances below the CH + (a 3 Pi ) threshold are resolved and classified using complex multichannel quantum defect theory. Scattering calculations with negative energy are used to obtain CH bound states. These yield a vertical ionisation energy in good agreement with experiment and estimates of the excitation energy to several excited states of 2 Pi and 2 Sigma symmetry, including some that have not previously been considered.