Knowledge Bank

In 1962, Rao and Venkateswarlu showed that a discharge through chlorine emitted a resonance fluorescence spectrum consisting of a long progression of close doublets. They showed that the fluorescence resulted from the excitation of $\mathrm{<mrow\; data-mjx-texclass="ORD">35</mrow>}Cl2$ a strong line of the spectrum of the chlorine atom and that the lower states of the fluorescence are the vibrational levels of the ground electronic state of $Cl2$. Unfortunately their resolution was insufficient to obtain the correct rotational and vibrational assignments. We have photographed the spectrum in the higher orders of a 10.6M spectrograph and have obtained an unambiguous assignment of the spectrum. We have also found that additional resonance progressions can be excited by placing the discharge in a magnetic field. The new spectra yield data on the J = 19 and J = 21 rotational levels of the ground electronic state almost up to the dissociation limit. These data have allowed us to calculate an RKR potential for the ground state of $\mathrm{<mrow\; data-mjx-texclass="ORD">35</mrow>}Cl2$ and in particular have allowed us to investigate the long-range Interactions between chlorine atoms.