Catastrophic dechannelling resonance (CDR) occurs when the half wavelength ( lambda /2) of a planar channelled ion beam matches the path length per layer, s, of a strained layer superlattice (SLS). CDR has been used for probing important properties of SLS. The dependence of CDR on various parameters, like incident angle, minimum impact parameter for channelling and superlattice strain in strained layer superlattices, are studied using a shell structure potential, which is based on the atomic shell structure of the target (SLS) atom. We have taken a GaAs_0.09P_0.91/GaP (s=48.2 nm) superlattice as our target and a ⁴He ion beam as the incident probe beam. Comparison with other frequently used Thomas-Fermi-type potentials and good agreement with experimental results shows the usefulness and accuracy of this shell model potential.