The Light Absorption of Vitamin BFormula

H. Kuhn, K. H. Drexhage, H. Martin
1965 Proceedings of the Royal Society A  
A calculation based on the one dimensional free electron model of the light absorp tion of vitamin B12 and of similar compounds has been carried out. The model was applied in its simplest form and in three stages of refinement by using a standard procedure described in a recent paper (Kuhn 1964) and tested there on a great number of dyes. The calculation was thus straightforward and no adjustable para meters were introduced. The interaction of the chromophore with the axial ligands was
more » ... igands was neglected as well as any effect depending on the specific nature of the central atom or on the buckling of the resonating portion. Table 1 -9 -8 -7 -6 -5 -4 -3 ■2 A (nm) (1) simple model 830 (2) m odel 1-fhetero-atom 590 pertu rb atio n (3) model 2 + p ertu rb atio n due 550 to bond length differences (4) m odel 3 + coupling effect 510 of tt electrons experim ent Co Ni 500 to 560 440 / 0-3 0-3 0-3 0-3 0-3 0-3 A (nm) 450 420 360 370 400 to 410 / 0-5 0-5 0-5 0-01 A (nm) 390 340 340 300 0-02 346 to 368 302 / 0-5 0-5 0-5 10 0-5 0*5 The seven lowest energy levels of the n electron system are filled and the first absorption band corresponds to the transition 7 -> 8 from the highest occupied state number 7 to the next state number 8, the next bands to the transitions 6-^-8 and 7 -> 9. Table 1 shows the wavelengths A and the oscillator stre n g th s/o f these bands as obtained by the simple model (model 1; electrons in a constant potential of length L = 14 lextending along the conjugated chain, where l = bond length), and by the models including the perturbation by the heteroatoms [ 348 ]
doi:10.1098/rspa.1965.0226 fatcat:yj3osdrip5ektacujmavm2miya