Study of C6− and C6 with threshold photodetachment spectroscopy and autodetachment spectroscopy

Abstract

The C6− anion and C6 neutral have been studied using both threshold photodetachment (zero electron kinetic energy) spectroscopy and autodetachment spectroscopy of C6−. The threshold photodetachment spectrum yields the electron affinity of linear C6 to high accuracy, along with the three symmetric stretch frequencies for linear C6 and the spin–orbit splitting in the ground 2Πu state of the anion. Two of the symmetric stretch frequencies are significantly lower than previous ab initio predictions. A simple model force field is used to calculate stretching force constants and estimate bond length changes between the anion and neutral. In addition, using autodetachment spectroscopy, we have located an excited electronic state of C6− that lies 43 cm−1 below the detachment threshold. This state is very similar in geometry to neutral C6. Excited vibrational levels of this state autodetach with rates that depend strongly on the available autodetachment channels. The excited state is tentatively assigned to a valence state, rather than an electrostatically bound state.