Fourier analysis was performed for the oscillatory yield curves obtained in experiments of low energy ion scattering spectroscopy (ISS) to facilitate the understanding of the underlying mechanism of the processes. Major components that appeared in the yield spectral density functions by the Fourier transform were responsible for oscillatory structures arising from the quantum mechanical interaction of the vacant 1 s state of incident He⁺ ions with the spin-orbit split 4f_7/2 and 4f_5/2 orbitals of Ta and W target atoms. Two major components at the frequencies of 1.6×10⁶ and 2.8×10⁶ cycles-m/s in the spectral density functions for the Ta target and one major component at the frequency of 1.5×10⁶ cycles-m/s for the W target were respectively assigned as attributable to the ISS quantum interferences.