Electronic Spectra of Aliphatic Carbonyls and Electron-phonon Couplings.

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Rigid matrices of aliphatic mono-carbonyls, such as acetone and acetoal-dehyde, generally give rise to very diffuse emission and absorption bands even at 4.2 k. No well-developped spectra have so far been reported except for the T-S absorption and emission spectra of hexachloroacetone in the crystal (M.KoyanGII et al., Chem.Phys., 5,107 (1974)). The main reason for this difficulty may greatly be attributed to inhomogeneous broadening whose origins are due to many geometrically different sites in one part and impurities produced during light irradiation in another part. The present work started with a plan that the latter problem was diminished as best as possible. For this purpose, crystal samples of mono-carbonyls at 4.2 k were lifted up at a speed of about 5 mm per minute using a synchronous motor during the optical measurements. This worked in part for acetone crystals : a band with a spacing of 300-400cm^<-1> was clearly observed. Technical difficulties coming from using such a large sample cell(50mm phi x 100mum), fluctuation of the sample cell, helium bubbling, etc. prevented us from ob-serving good S/N signals. Apart from this partial success, a well-developed S_1*S_0 absorption spectrum of hexachloroacetone was observed similarly. Asystematic series of research on the benzyl radical in the rigid matrices were very useful for us to take into account the role of impurities produced upon light irradiation in the host system.