Table 1.

Percentage of total Fe assigned to observed species

Sample	[2Fe-2S]2+	[4Fe-4S]2+	Fe2+	Fe3+
As isolated	0	100	0	0
2 min	31 (3)	38 (3)	10 (2)	≈20
17 min	33 (2)	5*	4	≈60

Because the Fe³⁺ compounds exhibit broad and unresolved spectra at 4.2 K, the fractions of Fe associated with these compounds are difficult to determine. However, the relative percentages of the other three species can be determined reasonably well from the spectra in Fig. 1. Numbers in parentheses give the estimated uncertainties. 

^*The spectral features suggest, but do not prove, the presence of a small amount of [4Fe-4S]²⁺ cluster.