Hyperfine measurements in the X and B electronic states of I35,37Cl: Probing the ionic character of the chemical bond

The laser induced fluorescence spectra of the B 3Π(0+)←X 1Σ+ electronic transition of I35Cl and I37Cl have been recorded with a linewidth of ∼5 MHz. This resolution allows the hyperfine splittings due to both nuclei to be measured. We report values for eQq0(I) and eQq0(Cl), for both I35Cl and I37Cl, for v′=0–2 and v″=0–2. This provides new data for both the ground and excited states. Information on the ionic character of the chemical bond of ICl in the X and B electronic states was deduced using a single electronic configuration [linear combination of atomic orbitals/molecular orbital (LCAO/MO)] model. The ionic character (fractional charge transfer) of the X state is −0.24 for v″=2, 1% less than for v″=0. Since the π and π* orbitals are completely filled for the X state, this ionic character is due entirely to the σ bonding orbital. For the B electronic state, the total ionic character was estimated from the dipole moment, and the hyperfine data were used to separately determine the ionic character of the σ type and π type molecular orbitals (−0.13 and −0.14, respectively). This is qualitatively consistent with the predictions given by the LCAO/MO model. However, the ionic character of the π type orbitals is observed to change rapidly with vibrational excitation, with the magnitude tending to zero at v′=2.