THE ALTERNATION WITH J OF ABSORPTION LINEWIDTHS IN THE $B^{3}II_{0_{u}}^{+}-X{^{1}}\Sigma_{g}^{+}$ BAND SYSTEM OF THE IODINE MOLECULE.

Author Institution: State University of New YorkWe have begun an experimental study of the shapes of absorption lines in molecular electronic spectra. The instrument being used in this study is an ``Hypeac'' pressure scanning Fabry-Perot interferometer spectrometer whose resolving power has been demonstrated to be at least 750,000 (corresponding to a line-width of $0.024 cm^{-1}$) at $5500\AA$. The first absorption spectrum we have studied is the $B {^{2}}II_{0+}-X{^{1}}\Sigma_{g}^{+}$ transition of iodine vapor at about $5600\AA$. The smallest measured linewidths in this spectrum are about $0.030 cm^{-1}$ at total pressures of $100 \mu$ Hg. The linewidth alternates with the rotational quantum number J. being about $0.030 cm^{-1}$ for even $J^{\prime\prime}$ and $0.035 cm^{-1}$ for odd $J^{\prime\prime}$. We have attempted to explain the observed width and its alternation in terms of the interaction of the nuclear quadrupole moment of the iodine nuclei with the molecular electric field