# Role of $\sigma-\pi$ interactions on linear and nonlinear susceptibilities in polyenes

Albert, IDL and Ramasesha, S (1991) Role of $\sigma-\pi$ interactions on linear and nonlinear susceptibilities in polyenes. In: Chemical Physics Letters, 182 (3-4). pp. 351-356.

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Official URL: http://dx.doi.org/10.1016/0009-2614(91)80228-P

## Abstract

The validity of the $\sigma-\pi$ separability approximation has been well established for some properties of the low-lying states in long polyenes. However, properties such as polarizabilities and hyperpolarizabilitles apparently depend upon the entire excitation spectrum of the molecule and a detailed study of the $\sigma-\pi$ separability approximation is warranted. We find from model calculations of the exact dynamic and static polarizability, $\alpha$, and third-harmonic-generation (THG) coefficient,$\tau$, in butadiene that the contribution of $\sigma$-electrons to the total polarizability is $\approx30\%$ while their contribution to THG coefficients is $\approx10\%$. The $\sigma$ electrons make a positive contribution to $\alpha$ while their contribution to $\tau$ is small and negative. It is, therefore, likely that the excited states contributing to $\alpha$ are not the same as those contributmg to $\tau$. The $\sigma-\pi$ separability approximation improves with increase in conjugation length and our calculations, being restricted to butadiene, provide an upper limit on the contribution of the $\sigma$-electrons.

Item Type: Journal Article Copyright of this article belongs to Elsevier Science. Division of Chemical Sciences > Solid State & Structural Chemistry Unit Dipti Chaurasia 15 Jul 2007 30 Jan 2012 05:11 http://eprints.iisc.ac.in/id/eprint/11565