Electronic transition of C3H- in the vicinity of the lowest photodetachment threshold

The electronic spectrum of the C3H(D)(-) anion has been studied near the lowest electron detachment threshold associated with the chain isomer. On the basis of the vibrational and rotational analyses, the photodetachment spectrum is assigned to the (3)A " <--(X) over tilde (3)A " electronic transition of the cumulene-like C3H( D) anion. The spectrum is characterized by a rich vibrational structure leading to the determination of almost all fundamental frequencies. The vibrational progression involving the CCH (D) in plane bending mode (nu'(6))is fitted with a 1-dimensional potential energy curve along the CCH( D) angle. This rt and the rotational analysis enable the geometry of the upper state to be determined. Although this excited state is expected to have dipole bound character, its neutral counterpart has a significantly different structure. The observation of an excited triplet state near the electron detachment threshold and close to the the calculated transition state for the electron catalysed isomerization reaction leads to new insight into this process.