Knowledge Bank

A Stark effect is observed in the rotational fine structure of the 0--0 band of the lowest-lying singlet $\Pi ^ * \leftarrow \Pi $ state of indole. The field applied is 26 kv/cm, with $SF6$ in the cell to prevent breaking down. Splittings are found in the Q branch, this enables us to find $\mid \Delta \mu \mid =0.14D$ from the ground state. The rather small change in dipole moment on excitation is in agreement with results for other $\Pi \ast \leftarrow \Pi$ transitions.