Knowledge Bank

Vibrational bands near the dissociation limit of the ICI $A3\pi (1)$ state have been examined using microwave-optical double resonance techniques. By using a single mode ring laser and a skinned molecular beam, hyperfine structure of the rotational lines is resolved at the MHz level. With Doppler linewidths of MHz. splittings in the optical transitions due to the chlorine nuclear quadrupole coupling are partially resolved. Analysis of these spectra results in values for the electric quadrupole and magnetic hyperfine constants which reveal changes in the electronic distribution of the molecule as it approaches dissociation. Applications of the method to the electronically excited states of polyatomic molecules will be discussed.