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 CP anion with the Σ ground state, which possesses dipole-bound excited states because neutral CP (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, corresponding to the two spin-orbit states of neutral CP (Π and Π). The current study demonstrates that the weakly bound electron in the dipole-bound excited states of CP is not spin-coupled to the electrons in the CP core and can be considered as a quasi-free electron.