The cross section for photodetachment of C2 is investigated in the photon energy range 14 000–20 000 cm−1 (1.75–2.5 eV). Sharp resonances due to autodetachment are observed at photon energies corresponding to transitions between high vibrational levels of the C2X2Σg+ state and high vibrational levels of the C2B2Σu+ states. The resonances are narrower than 6 GHz, and those arising from the v=5 level of the B state are about 1/10 as strong as those arising from the v=6 and higher levels. In addition, the signal from the allowed direct photodetachment of C2X state, which would produce a smooth background cross section, is not observed, indicating that it is less than the 103 peak to background contrast ratio. A rotational analysis of the nine bands of the C2BX transition observed in this study, coupled with previous measurements provides a new, more precise set of spectroscopic constants for these states. These constants are then used to generate RKR potential curves for the B and X states of C2. Based on all C2 data, the only consistent interpretation of the observations is that the electron affinity of C2 is bounded by 3.374 eV ?EA(C2)?3.408 eV. The autodetachment rate into (C2a3Πu+e) is deduced to be much faster than the rate into (C2X1Σg++e), probably as a result of strongly R dependent configuration interaction in the C2B state. The weakness in the direct photodetachment process is attributed to poor vibrational overlap between the initial and final states.

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