Basic molecular processes for hydrocarbon spectroscopy in fusion edge plasmas: vibrationally state-selective excitation of A2Delta, B2Sigma- and C2Sigma+ states of CH by electron impact

Quantification of chemical erosion in fusion edge plasmas is often based upon CH (Ger¨o-band) spectroscopy. Systematic, vibrationally resolved rate coefficients for the electron impact excitation of A2Delta, B2Sigma- and C2Sigma+ electronic states of the CH molecule are presented in the temperature range 0.2-1500 eV. The rate coefficients for 0-0 vibrational transitions are based on the R-matrix cross sections for energies below 10 eV, Born-Bethe cross sections for energies above ~25-30 eV and a smooth interpolation in the 10-20 eV energy range. The rate coefficients for the v-v transitions are determined by using a scaling relationship. The implications of these results for the fusion edge/divertor plasma diagnostics, based on the A(v) -> X(v) transitions, are discussed. The rate coefficients for the 0-0 transitions are presented by convenient analytic fit expressions.