Theory of the Optical Absorption of β-Carotene

The optical absorptions of all -trans and 15- cis β-carotene with non-planar configuration are calculated by means of our previous LCAO-ASMO-SCF-CI formulation for π-electrons, taking account of the screening of two-center Coulomb repulsion integrals for all the pairs of atoms except bonded ones. It is thus shown that the cis -peak of 15- cis β-carotene is caused both by the loss of center of symmetry in the cis configuration and by the twisting around C 14 –C 15 and C 15' –C 14' single bonds. It is also shown for 15- cis β-carotene that the angle between transition moments of the first peak and the cis -peak is 90° or not so much different from 90°.