Hyperfine analysis of the mixed A 3Π1 v=28 and X 1Σ+ v=69 states of I35Cl

The A 3Π1 v=28 state of I35Cl is known from previous studies to be strongly mixed with v=69 of the X 1Σ+ state. Spectra of both these mixed states are taken at high resolution to allow accurate measurement of the hyperfine splittings due to the iodine nucleus. The hyperfine structure in both parity components of the A state is found to be perturbed, though the common rotational-electronic induced mixing should only affect the e components. Detailed analysis shows that hyperfine terms in the Hamiltonian also contribute significantly to the rovibronic state mixing. A Hamiltonian for these states is described that accounts for the hyperfine structure in both the A and X states to within the observed linewidth. The hyperfine parameters of this Hamiltonian, including the perturbation parameters, can be accounted for semi-quantitatively in terms of a separated atom model.