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Abstract
The 4K absorption spectrum and 4K magnetic circular dichroism (MCD) spectrum at 4·75 T are reported for MnO4 - in tetragonal KIO4 in the region of the first allowed charge-transfer transition (17 000–21 000 cm-1). Resolved vibronic structure is assigned to a major progression in the a 1(v 1) Mn-O stretching mode, overlapping a short progression in the b 2(D 2d ) component of the t 2(Td, v 4) Mn-O stretching mode. Relative dipole strengths and MCD A and B terms are obtained by moments analysis of each individual member of the vibrational progression. The values of A/D are all much smaller than expected in the absence of vibronic interaction, and those of B/D change sign along the progression. Both these effects are explained by the interaction of the 1 E(D 2d ) component of 1 T 2 with the b 2(D 2d ) component of the t 2(Td ) vibrational mode. Calculated and observed values of A/D and B/D are in good agreement for a value of the Jahn-Teller stabilization energy equal to about half the zero-point vibrational energy.