A distorted-wave theory based on a hard-corrugated-wall potential with a time-dependent modulation (dynamic corrugation) and accurately calculated surface-projected phonon densities is used to calculate the relative amplitudes of time-of-flight spectra. The calculated spectra are compared with measured spectra over a wide range of angles. In general, good agreement is obtained under conditions where final-state resonances with bound states of the atom-surface potential are not expected. When these resonance processes occur, anomalies are found in the measured spectra. The results indicate that single-phonon processes dominate the measured spectra and that under certain conditions bulk modes can affect the spectra. Resonance processes may be useful in enhancing otherwise weak interactions.