Electron collisions with methylidyne (CH) radical using the R-matrix method

The R-matrix method is used to calculate the elastic and the excitation cross sections from the ground state X(2)Pi to the four low-lying electronically excited states a(4)Sigma (-), A(2)Delta, B(2)Sigma (-) and C(2)Sigma (+) of methylidyne (CH) radical. Configuration interaction (Cl) wavefunctions are used to represent the target states. In our CI model we keep the 1 sigma orbital doubly occupied and the remaining electrons are free to occupy the 2 sigma, 3 sigma, 4 sigma, 1 pi, 2 pi, 3 pi and 1 delta orbitals. This model gives an equilibrium bond length, R-e, of X(2)Pi state equal to 2.113 a(0) which is in excellent agreement with the experimental value of 2.116 a(0) and a CH equilibrium dipole moment of 1.53 D which is close to the experimental value of 1.46 +/- 0.06D. Scattering calculations are performed in the static-exchange, static-exchange plus polarization, 5-state and 6-state models. Our best 6-state model also includes the D(2)Pi state. The vertical excitation energies lie in the range 0.32-7.29 eV and agree within three per cent of the, symmetry with experimental values. We find a bound state of CH- of (3)Sigma (-) electron affinity of 0.61 eV at R-e. Below 1 eV there are shape resonances in (1)Sigma (+) and (1)Delta symmetries. Both of these resonances have the configuration 3 sigma (2)1 pi (2). Born correction is applied for dipole-allowed transitions to account for higher partial waves excluded in the R-matrix calculation. Cross sections are given for scattering energies up to 10 eV.