Knowledge Bank

Fluorescence excitation spectra of the $A,3\Pi (1)\leftarrow X,1\Sigma \ast$ electronic transition of $I35Cl$ has been obtained by using a single frequency dye laser and a well collimated molecular beam. Data was collected for 11 vibrational levels in the range $V+=11$ to 34 ($Vmax+=35$). Of these 11 levels, 10 were sufficiently resolved to fit the splitting due to the nuclear spins of both nuclei in the molecule. The nuclear hyperfine constants obtained from our fit were found to be unique in that the signs of the magnetic (a) and scalar electric quadrupole ($eQqo$) constants are opposite for the two nuclei. This result is not compatible with that obtained using a LCAO/MO basis for the formation of the molecular wave function. Since the Internuclear separation is large, on average, for the high vibrational levels \AA for $V1=34$) a separated atom basis was employed to analyze the measured hyperfine constants. Based on this analysis it was determined that the vacant orbital on the Cl atom has 55% P, character for \AA, while that of the I atom has only 15% $px$ character. The meaning of this result and the effect, on the valence electronic charge distribution, of changing the average vibrational Internuclear separation will be discussed.