No abstract

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

No abstract

SCF-Xα-SW calculations have been performed for H2S in the ground state, in ionic states resulting from the vertical removal of a valence electron, and in 36 singlet and triplet excited states resulting from the vertical excitation of an electron from the 2b1 or the 5a1 molecular orbitals to various virtual orbitals. Excellent agreement for the transition energies is found both with the experimental ultraviolet and photoelectron spectra and with recent large-scale configuration interaction calculations. The average absolute difference between the Xα-SW and CI results for the 26 cases where both exist is only 0.24 eV. The intrinsic advantages of the Xα-SW method over the traditional LCAO or one-center approaches for the treatment of Rydberg states are delineated. Contour plots of the excited orbitals have been generated and these are used to illustrate some of the conceptual problems related to the Rydberg-valence distinction. Finally, a brief speculative discussion of the possible photochemical implications of the character of the two excited orbitals involved in the first absorption band is given.

Photoelectron spectra of polynuclear aromatics. V. Correlations with ultraviolet absorption spectra in the catacondensed seriesThe HeI photoelectron and ultraviolet absorption spectra of the oximes and O-methyloximes of a series of conjugated Schiff bases have been determined. The importance of the low ionization potentials of these compounds is stressed, especially in connection with the chromophore of visual pigments. The location of the (1T ,1T.), (n ,1T-), and lowest Rydberg bands in the UV spectra is discussed. 256

Beweise für eine Disproportionierung von photolytisch aus Bis‐[trimethylsilyll‐Hg‐ Dampf erzeugten Trimethylsilyl‐Radikalen zu Tiimethylsilan und Me2Si=CH2 werden mitgeteilt.