Electronic spectra of conjugated dye and test of free electron model
A. N.S. Bayliss, A "Metallic" model for the spectra of conjugated polyenes, J. Chem. Phys, 16, 287 (1948).
B. H. Kuhn, Free electron model for absorption spectra of organic dyes, J. Chem. Phys, 16, 840 (1948).