UV–visible absorption bands and molar absorptivities

Literature wavelengths and ε for the solutions on the virtual spectrophotometer, beside the ε the site’s teaching fit gives at the same wavelength — the two agree within a few per cent.


$\ce{MnO4-}$	Potassium permanganate	526	2400	2450	band maximum	526, 547	purple
$\ce{MnO4-}$	Potassium permanganate	546	2380	2366	band maximum	526, 547	purple
$\ce{MnO4-}$	Potassium permanganate	440	95	90	flank or shoulder	526, 547	purple
$\ce{Cr2O7^2-}$	Potassium dichromate (dilute H₂SO₄)	350	3136	3136	band maximum	—	orange
$\ce{Cr2O7^2-}$	Potassium dichromate (dilute H₂SO₄)	430	468	469	flank or shoulder	—	orange
$\ce{Cr2O7^2-}$	Potassium dichromate (dilute H₂SO₄)	440	369	380	flank or shoulder	—	orange
$\ce{Cr2O7^2-}$	Potassium dichromate (dilute H₂SO₄)	545	11	11	flank or shoulder	—	orange
$\ce{[Cu(H2O)6]^2+}$	Copper(II) sulfate	800	12	12	band maximum	800	pale blue
$\ce{[Cu(NH3)4(H2O)2]^2+}$	Tetraamminecopper(II)	605	52	52	band maximum	605	deep blue
$\ce{FeSCN^2+}$	Thiocyanatoiron(III)	447	4700	4700	band maximum	447	blood red
$\ce{[Fe(phen)3]^2+}$	Tris(phenanthroline)iron(II)	510	11100	11119	flank or shoulder	501	orange-red

The fitted bands are Gaussians in wavenumber (a vibronic progression for KMnO₄) and are reliable only near the literature values; ε for K₂Cr₂O₇ is per mole of dichromate dissolved — in dilute solution Cr(VI) is mostly HCrO₄⁻.

Sources

D. C. Harris, Quantitative Chemical Analysis, 9th ed. (2016), ch. 18–19 (MnO₄⁻ ε ≈ 2.4 × 10³ at 525 nm).
D. A. Skoog, D. M. West, F. J. Holler, S. R. Crouch, Fundamentals of Analytical Chemistry, 9th ed. (2014), ch. 26 (MnO₄⁻ and Cr₂O₇²⁻ at 440 and 545 nm).
European Pharmacopoeia 2.2.25, control of absorbance with potassium dichromate (350, 257, 313 and 430 nm).
G. den Boef et al., Recl. Trav. Chim. Pays-Bas 77 (1958), doi:10.1002/recl.19580771110 (permanganate spectrum).
H. S. Frank, R. L. Oswalt, J. Am. Chem. Soc. 69, 1321 (1947) (FeSCN²⁺); W. B. Fortune, M. G. Mellon, Ind. Eng. Chem. Anal. Ed. 10, 60 (1938) ([Fe(phen)₃]²⁺).
C. E. Housecroft, A. G. Sharpe, Inorganic Chemistry (copper aqua and ammine bands).

Sources

Used in these lessons