The 4f, v = 0 manifolds of levels of ArH, ArD, and KrD observed by Dabrowski et al. [J. Mol. Spectrosc. 189, 110 (1998)] and Dabrowski and Sadovskii [J. Chem. Phys. 107, 8874 (1997)] have been reanalyzed using multichannel quantum defect theory. The nondiagonal (l-mixing) quantum defect matrices are partially extracted from the experimental data and are found to be in reasonable agreement with the quantum defects calculated theoretically by Jungen et al. [Phil. Trans. R. Soc. Lond. A 355, 1481 (1997)]. The quantum defect calculations reproduce the observed level fine structure in great detail including nonadiabatic rotational l-uncoupling and electronic l-mixing perturbations.