THRESHOLD PHOTOELECTRON-SPECTROSCOPY OF I-2

The threshold photoelectron spectrum of molecular iodine has been measured at a resolution of 6-8 meV using synchrotron radiation in the region 9-14 eV and a penetrating-field electron spectrometer. The spectrum reveals resolved vibrational structure in each spin-orbit component of the X ((2) Pi(g,i)) state of I-2(+), which arises as a result of both direct photoionization and autoionization processes. In addition, extensive resolved vibrational structure has been observed in the A ((2) Pi(u,i)) state of I-2(+) for the first time in any electron spectroscopic study. The average vibrational spacings were as follows: 220(8) cm(-1) in X ((2) Pi(g,3/2)), 214(8) cm(-1) in X ((2) Pi(g,1/2)), and 120(8) cm(-1) averaged over both spin-orbit components in A ((2) Pi(u,i)).