Laser photoelectron spectrometry of C5H−5: A determination of the electron affinity and Jahn–Teller coupling in cyclopentadienyl

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Abstract
The photodetachment electron spectrum of cyclopentadienide (C5H−5) yields a value for the cyclopentadienyl electron affinity of 1.786±0.020 eV. Additionally, the spectrum shows structure corresponding to vibrations in the neutral radical. From this an upper bound is placed on the linear Jahn–Teller coupling constant k2Dn or Cn groups when n is not divisible by three. The magnitude of this Jahn–Teller distortion is sufficient to induce nontotally symmetric Jahn–Teller modes in the spectrum, but is insufficient to suppress the symmetric modes and, in particular, a strong 0–0 transition is observed. Thus, the geometries of the ion and the neutral, apart from the Jahn–Teller distortion, are not radically different.