Photodetachment spectroscopy of the C[sub 2n]H[sup -] (n=2–4) anions in the vicinity of their electron detachment threshold.

The electronic spectra of the C[sub 2n]H(D)[sup -], n = 2-4, anions have been observed in the gas phase using photodetachment spectroscopy. These are assigned to ¹Π ← X¹Σ[sup +] electronic transitions. The ¹Π excited states possess a dipole bound character indicated by the energetic proximity between the origin of the transitions and electron affinities. The dipole bound states are related to the X²Π ground states of C[sub 6]H and C[sub 8]H whereas for C[sub 4]H, which has an X²Σ[sup +] ground state, the ²Π is an excited state. Vibronic coupling through a bending motion of the carbon skeleton is inferred to be the reason of the stabilization of this state. [ABSTRACT FROM AUTHOR]