PARAMETRIC METHOD IN THE THEORY OF THE VIBRONIC SPECTRA OF COMPLEX-MOLECULES - ABSORPTION-SPECTRUM OF DECAPENTAENE

The absorption spectra of decapentaene are analyzed and calculated usi ng the available efficient methods of calculating the matrix elements of the vibronic problem, a new parametric method for determining the p otential surfaces of excited molecules, and a fragmentation approach t o the design of molecular models. Good agreement for the fine vibratio nal structure of the calculated and experimental spectra (differences between the main band frequencies and intensities less than 20 cm(-1) and 10%, respectively) is obtained without correcting the parameters o f the method. The mechanisms of excitation-induced structural changes in linear polyenes and the effect of bond angle changes on the vibrati onal structure of the spectrum are revealed. A new interpretation of t he absorption spectrum of decapentaene in an argon matrix is proposed [J. Mel. Spectrosc, 114, 54-59 (1985)]. It is shown that the parametri c method allows quantitative prediction of fine structure for the vibr onic spectra of complex molecules.