Triplet to singlet excitation of C v ions in high-temperature plasmas

Measurements of the relative intensities of C V 2 1 S-2 1 P (3541 Angstrom), C V 2 3 S-2 3 P 2 (2271 Angstrom) and C IV 4 2 D-5 2 F (2524.4 Angstrom) lines from relatively low-energy (similar, equals 12.5 kJ) theta-pinch discharges in methane (electron density similar, equals 4 × 10 17 cm -3 , electron temperature kT e similar, equals 40 eV) are reported. From these experimental data, the total triplet to singlet excitation rate coefficient amongst the n = 2 levels of the C V ion is estimated to be about 4 × 10 -9 cm 3 s -1 at kT e = 37 eV with an overall uncertainty of about a factor of 2. This observed value is substantially in agreement with the predicted maximum theoretical value for s-wave electrons.