The third point to make is that the relative intensities of the peaks in the cryo-SEVI spectra differ markedly from those in the PE spectrum. Moreover, the relative intensities in the overview and high resolution cryo-SEVI spectra are very different. For example, the relative intensity of the vibrational origin, peak A, clearly drops relatively to that of peak B, the 4 0 1 transition, as we progress from the PE spectrum to the overview spectrum and then to the high-resolution composite spectrum. These spectra are taken at progressively lower photon energies, so the eKEs of the two peaks are dropping in this progression of spectra. According to the Wigner threshold law, Eq. ( ), the photodetachment cross section drops with decreasing eKE, but it drops more abruptly at higher values of l. Hence, peak A appears to undergo photodetachment at a higher value of l than peak B.