Absolute cross section for C2+ (2s2p Po3 →2 p2 P3) electron-impact excitation

We have measured the absolute energy-averaged cross section for the electron impact excitation of C2+ (2s2p Po3 →2 p2 P3) from energies below threshold to 17 eV above, and present the measured absolute rate coefficients for this transition, for temperatures from 104 to 105 K. These rate coefficients are required for diagnostics of plasmas such as those found in astrophysical environments. The synchronous photon detection method with beams modulation and inclined electron and ion beams was used. Radiation at 117.6 nm from the decay of the excited ions back to the metastable state was detected using an absolutely calibrated optical system. The fractional population of metastable C2+ (2s2p Po3) in the incident ion beam was determined to be 0.42±0.03(1.65 σ). The rate coefficient for log10 T=4.8 was determined to be 1.01× 10-8 cm3 s-1 ±14% at a 90% confidence (1.65 σ) level. The measured cross section is in agreement within experimental uncertainty with 6-term close-coupling R -matrix calculations and 90-term R matrix with pseudostates calculations.