Nature of the Visible Charge-Transfer Bands of K3Fe(CN)6

Abstract

The temperature dependence of the 20–28 kK optical absorption in K3Fe(CN)6 crystal is negligible below room temperature. The inference is made that this charge-transfer absorption is electronically allowed (u←g). An alternate interpretation of Naiman that the band is of (g←g) type and thus activated by vibrations is not disproven, but it is restricted such that very stiff modes—i.e., those involving CN stretching— would have to be the only effective vibrational promoters. Arguments are made against this possibility.