High-resolution inelastic He atom:scattering experiments have been used to measure the transverse optical mode on an in situ cleaved NaCl(100) crystal surface at a crystal temperature of 100 K in the (110) direction. The bound states of NaCl(001) lead to many resonance features in the time-of-flight spectra which act to obscure the desired surface phonon information. However, since the bound state energies are known, the resonance features are identified and removed. A slab calculation using the breathing shell model and surface perturbations which fulfill translational and rotational invariance conditions are used to interpret the measured surface phonons.