where 𝒙 and 𝒚 are sets of MS 2 mass spectra collected at 𝐸 > 0 different collision energies, 𝒙 ' and 𝒚 ' are the specific mass spectra collected at the same 𝑖th collision energy, 𝜖 ($ = 0.005 is the m/z tolerance with a high resolution mass spectrometer, and the pairwise spectral similarity function 𝜃 is the same as employed with EI-MS mass spectra. If Δ %&! ≤ 𝜖 ($ = 0.005, and the compared compounds do not share any MS 2 spectra at the same collision energy, then 𝜙 ) (𝒙, 𝒚) = 1.