Acc. zyxwvuts Chem. Res. zyxwvu 1992,25, 299-307 299 the primary step of zyxwvut eq 12. For the adsorbed phase, the secondary product C2H4along with CO is observed.77 Acetylene photochemistry by 185 nm produces the radicals H and C2H' in the gas phase and a number of secondary pr0du~t.s.~~ The adsorbed-phase reaction 13 is by contrast remarkably clean, with hydrogen ex- change among isotopomers the only evidence for chem- istryYs Finally, 185-nm gas-phase photochemistry of SO2 produces SO and 0 and secondary reactions gen- erate However no reaction for zyxwvu this system occurs in the adsorbed phaseY9 It is likely that the arrange- menta of the excited adsorbed species play a crucial role in the resulting photo~hemistry.'~ While the mecha- nisms of adsorbed-phase photochemistry on dielectric substrates have been explored for LiF(lOO):g* we view the understanding of simple adsorbed-phase reactions like those in eqs 12-14 to be essentially lacking. Finally, we turn our attention to the most poorly understood (but likely most important) energy pro- (76) zyxwvutsrqp Okabe, H. Photochemistry of Small Molecules; Wiley: New York, (77) Berg, 0.; Ewing, G. E. J. Phys. Chem. 1991,95, 2908. (78) Dunn, K. Private communication. (79) Berg, 0. Private communication. 1978. cesses at salt surfaces. Here the surfaces are on par- ticulates thrown into the atmosphere by the world's oceans. The salt particulates are freed of halides by reaction with sulfur and nitrogen oxides from anthro- pogenic and natural sources.w2 While these chemical exchange processes have been reproduced in the labo- ratory for gas-phase reactions with both liquidE2 and solid surfaces,83 the mechanisms for the reactions have not been established. We believe the spectroscopic techniques described in this Account may help elucidate these mechanisms. We gratefully acknowledge the thughtful research of members and former members of our group at Indiana University who have provided much of the science for this Account. We thank the National Science Foundation (CHE88-14717) and the donors of the Petroleum Research zyxw Fund, administered by the American Chemical Society, for their financial support. Regietry No. NaC1, 7647-14-5. (80) Hitchock, D. R.; Spiller, L. L.; Wilson, W. E. Atmos. Enuiron. (81) Junge, C. E. Tellw 1956,8,127. (82) Robbine, R.; Cadle, R.; Eckhardt, D. J. Meteorol. 1959,16, 53. (83) Finlayson-Pitta, B. J.; Livingston, F.; Besko, H. Nature 1990,343, 1980,14, 165. Cadle, R.; Robbim, R. Discuss. Faraday Soc. 1960,30,155. 622. Photochemical and Photophysical Studies of Organic Molecules Included within Zeolites? V. RAMAMURTHY,* D. F. EATON, and J. V CASPAR Central Research and Development, Experimental Station, The Du Pont Company, Wilmington, Delaware 19880-0328 Received February 10,1992 Introduction Being inspired by and having realized the complexity of natural systems, chemists have utilized a number of organized/confiied media to study the photochemical and photophysical behavior of guest molecules. Exam- ples of organized media in which the guest molecules' behavior has been investigated include molecular V. zyxwvutsrqponmlkj Rememuthy, after obtaining mhhg In zyxwvutsrqpo photochemistry under the d b tbn of R. S. H. UU (University of Hewall, W.D., 1974), P. de May0 (University of Western Ontarb, posMoctora1 rooO81ch. 1974-1975), and N. J. T m (Co- lunh Untverdty, postdoctag1 research, 1975-1978), joined the fatuity of the Dept" of chgank chmislJy, Inean InstlMe of science, Bangabre, India, where he remained untll 1987. In 1987 he Joined Du Pont Csniral Reecurrch and Devdopment, Wwmington, DE, as a n'mmbor of the research staff where he contlnucw hk interest In the area of orgenlc photochernMy. Dad F. Eaton Is Research Managsf, Materleb Science, wlthln Du Pont centre1 Research and Development wlth respondbl#ty for rower& prcgrame in 7, organicandinorganlc nonlmwrroptlcs, andWn film physics. Hk educatbn was obtehed at W a y a n Unhrerdty (A.B., 1968) and Caltsch (W.D., mnlc chernWy, 1972). He has wotked In several areas of phb chemMyandphotdmeginOdvkrghkceireerwlthDuPont. J. V Caspar received Ms B.S. (1978) degee from the Massachusetts In- stltute of Techdogy. After cunpktino hie W.D. (1982) at the University of North Caroyna at ape4 HYI under the diredon of 1. J. Meyer, tm qmnt a year as a Poadoctorel FeyOw wtth H. B. Qray at the Cayfomla Institute of T - . Hejolwdthe Centre1 Research and Devekpmnt- atDuPontasa~oftheresearchstaffin1983. Hlslnterestscontinw to rewoke around diverw areas of photochemistry, photophysks, and ape& troacopY. OOO1-4842/92/0125-0299$03.00/0 crystals, inclusion complexes (both in the solid and solution states), liquid crystals, micelles and related assemblies, monolayers, LB films, surfaces, and more recently natural systems such as DNA.' The studies carried out thus far come under the following categories: (a) influence of media on the photochemistry and photophysics of molecules; (b) photochemistry and photophysics as a tool to understand the media; (c) influence of photochemistry and photophysics on the media; and (d) studies directed toward applications- devices, solar energy, biological implications. In this Account an overview of the activities in our laboratory, Contribution No. 6177. (1) Fox, M. A., Ed. Organic Phototransformation in Non-homoge- neow Media; American Chemical Society: Waehington, D.C., 1985. Thomas, J. K. Chemistry of Excitation at the Interfaces; American Chemical Society: Washington, D.C., 1984. Ramamurthy, V., Scheffer, J. R., Turro, N. J., Eds. Organic Chemistry in Anisotropic Media. Tetrahedron Symposia in Print 29. Tetrahedron 1987,43,1197-1746. Kalyar~undaram, K. Photochemistry in Microhetwogeneow Systems; Academic Press: New York, 1987. Matsuura, T., Anpo, M., Ede. Pho- tochemistry on Solid Surfaces; &vier: Amsterdam, 1989. Balzani, V.; scandola, F. Supramokculur Photochemistry; Ellis Horwood: New York, 1991. Schneider, H. J., Durr, H., E&. Frontiers in Supramolecular Organic Chemistry and Photochemietry; VCH Weinheim, 1991. Honda, K., Ed. Photochemical Processes in Organized Molecular Systems; North-Holland Amsterdam, 1991. Ramamurthy, V., Ed. Photochem- zy istry in Organized and Constrained Media; VCH New York, 1991. 0 1992 American Chemical Society