(b) The first photoelectron band system of Oz (i.e ionisation to the ground electronic state of O2 ") shows a limited vibrational progression, peaking at v* = 1. The second photoelectron band system (i.e. ionisation to the first excited electronic state of O2 ") shows an extensive vibrational progression peaking at v = 8. What do these facts indicate about the nature of the two highest- occupied valence molecular orbitals of Oz