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Abstract— Model studies including quantum chemical calculations and the measurement of infrared and ultraviolet spectra are presented as contributions to the elucidation of the nature of the photochemical step of vision. The importance of the hydrogen bond in which the protonated nitrogen of the retinal Schiff base is involved is stressed as well as that of the perturbation of the β‐ionone ring by negative groups. It is suggested that by combining these two perturbations the low excitation energy of rhodopsin can be obtained without actual protonation of the Schiff‐base prior to photon absorption. The variation of rhodopsin's color from one species to another could also be related to this. Protonation could be a consequence of photonabsorption and the higher basicity of the excited state. This, in turn, leads to the suggestion that the protonated species is actually bathorhodopsin, not rhodopsin. Comments are made on the identity of the (ππ*) state which is involved.

The HeI photoelectron and vacuum uv absorption spectra of a number of methyl, ethyl, methylfluoro, and ethylfluoro derivatives of silane are presented. The spectra can be interpreted on the basis of their similarity to those of the related methane or ethane derivatives. The lowest lying excited states are related to transitions to 4s, 4p, and 3d orbitals having mixed Rydberg–valence shell character. The spectra can be divided into two categories: methane (’’round field’’) or ethane (’’long field’’) types. Fluorine substitution influences these spectra in a characteristic way.

A final point of interest is an increase at long irradiation times (> 12 h) of the yield of Me3COSiMe3 and a concomitant decrease in the yield of Me3SiSiMe3. Trapping experiments with labeled alcohol indicate that photolysis of hexamethyldisilane is another route to 2-methyl-2-silapropene. This has also been observed by Boudjouk and Koob in the gas phase.12 Me3SiSiMe3 + hv-* Me3SiH + CH2=SiMe2Acknowledgments. We thank Professor Thomas J. Barton for stimulating discussions of this problem and for helpful suggestions; we also thank Mr. Daniel Graham for mass spectrometric analyses. Financial support from the Department of Energy is gratefully acknowledged. This is technical report COO-1718-78. References and Notes

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