# BIG ORBITS IN SMALL MOLECULES.

Please use this identifier to cite or link to this item: http://hdl.handle.net/1811/15231

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 Title: BIG ORBITS IN SMALL MOLECULES. Creators: Robin, M. B.; Basch, Harold; Kuebler, N. A. Issue Date: 1967 Publisher: Ohio State University Abstract: There is in the spectra of olefins, a weak absorption band preceding the $N\rightarrow V$ transition, the assignment of which has been the topic of recent debate. Though most agree that the olefin mystery band'' must involve sigma orbitals, it has not been made clear whether the assignment is $\pi \rightarrow \sigma^{\ast}$ or $\sigma \rightarrow \pi^{\ast}$, nor is it clear just what $\sigma^{\ast}$ really is. Recent spectroscopic experiments on selected olefins in high pressure $N_{2}$ gas and as solutes in rare gas matrices demonstrate that the question as to whether the mystery band is assigned as $\pi \rightarrow \sigma^{\ast}$ or $\sigma \rightarrow \pi^{\ast}$ is meaningless. This follows from the fact that olefins really have several low lying mystery bands, some $\pi \rightarrow \sigma^{\ast}$ and some $\sigma \rightarrow \pi^{\ast}$. All electron, indirect SCF calculations show that in ethylene, the four lowest $\pi \rightarrow \sigma^{\ast}$ states are big orbit, Rydberg-like, whereas the $\sigma \rightarrow \pi^{\ast}$ states are strictly valence shell. A similar situation has developed in the spectra of amides, where a mystery band has been found between the $n \rightarrow \pi^{\ast}$ and lowest $\pi \rightarrow\pi^{\ast}$ excitations. Calculations and experiments together suggest that the amide mystery band is a big orbit $n \rightarrow \sigma^{\ast}$ excitation. Description: Author Institution: Bell Telephone Laboratories Incorporated URI: http://hdl.handle.net/1811/15231 Other Identifiers: 1967-H-3