Probing the coupling of a dipole-bound electron with a molecular core

A dipolar molecule can weakly bind an electron in a diffuse orbital. However, the spin–orbit coupling between this weakly bound electron and the electrons in the molecular core is not known. Here we probe this coupling using the linear C(2)P(–) anion with the (3)Σ(+) ground state, which possesses dipole-bound excited states because neutral C(2)P ((2)Π) has a sufficiently large dipole moment. Photodetachment spectroscopy and resonant photoelectron spectroscopy are used to probe the nature of the dipole-bound states. Two dipole-bound excited states are observed with a binding energy of 37 cm(–1), corresponding to the two spin–orbit states of neutral C(2)P ((2)Π(1/2) and (2)Π(3/2)). The current study demonstrates that the weakly bound electron in the dipole-bound excited states of C(2)P(–) is not spin-coupled to the electrons in the C(2)P core and can be considered as a quasi-free electron.