Normal‐coordinate analysis of β‐carotene isomers and assignments of the Raman and infrared bands

Normal‐coordinate calculations were performed for the all‐ trans , 7‐ cis , 9‐ cis , 13‐ cis , 15‐ cis , 9, 13‐di‐ cis , 9,13′‐di‐ cis , 9,15‐di‐ cis and 13,15‐di‐ cis isomers of β‐carotene. The Raman and infrared bands of the all‐ trans and 15‐ cis isomers in the solid state were assigned on the basis of the results of the normal‐coordinate calculations. The Raman excitation profiles of the main Raman bands of the above two isomers in cyclohexane solution reported previously were satisfactorily correlated with the calculated vibrational modes and the molecular structures in the excited electronic states. The Raman bands of the 7‐ cis , 9‐ cis , 13‐ cis , 9,13‐di‐ cis , 9,13′‐di‐ cis , 9,15‐di‐ cis and 13,15‐di‐ cis isomers were assigned. The vibrational modes assigned to the Raman bands characteristic of the cis isomers were analysed in detail.