Distribution of S/N obtained in the selected K_p – V_rest interval by shuffling 250 times the time order of the observed spectra, for each of the four selected chemical species. The vertical dashed (dash-dotted) lines represent the borders of the intervals enclosing the 95% (99.73%) of the S/N values, corresponding to the 2.5% − 97.5% (0.135% − 99.865%) quantiles of the distributions. These intervals are reported in Table 4.