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In situ, interference-enhanced Raman scattering of ultrathin, solid solution films of Rb x C60 (0o alkali fullerides is the microscopic origin of superconductivity at moderately high temperatures [1-3]. A number of mechanisms have been discussed, including electronic effects, as well as different electron-phonon coupling theories [4,5]. The latter differ regarding the specific importance of low-and high-frequency intramolecular phonons. While variations in the transition temperature with lattice constant [6] are broadly consistent with the role of the electronic density of states and possible electronphonon coupling, direct support for strong phonon coupling or details of the modes involved have not been presented to date. Two recent theories of phononmediated superconductivity in A x C(>o have emphasized that the intramolecular modes coupling C6o-derived n states at the Fermi energy are those with Raman activity [4,5]. This study presents detailed measurements obtained on ultrathin films of Rb x C6o that directly address such electron-phonon coupling.Ultrathin films of pure C6o, Rb x C6o, and K x C6o were deposited on low-reflectance multilayer structures that yield interference-enhanced Raman scattering (IERS). Such multilayers have allowed IERS studies of ultrathin films and clusters of average thickness less than one monolayer (ML) [7]. An -80-A-thick polycrystallineBi film was employed as the top layer, since weak interactions between C6o and Bi were noted for the Raman spectra of 1 ML of C6o. In situ, UHV Raman scattering at 300 K, for unanalyzed scattered light, employed 514.5nm Ar excitation and a Spex Industries Triplemate with an ITT Mepsicron multichannel detector. In order to minimize laser beam heating effects, focusing with a cylindrical lens and low laser power density of ~0.5 W/cm 2 were employed.Depositions of C6o, Rb, and K were performed on ^300-K substrates in a load lock of a UHV system at a pressure of ~~10 -8 Torr. Transfer into the UHV system at a base pressure of 2xl0~1 0 Torr was made immediately after sublimation of Rb or K from well baked out SAES Getter sources. The thickness of C60 utilized for most studies of 4 ML was calibrated with a crystal thickness monitor. Utilization of this ultrathin layer of C6o allowed the use of the same samples for both Raman scattering an He I ultraviolet photoemission (UPS) for

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Laser-excited states in films of pristine C 60 and photopolymerized C 60 (pp-C 60 ) prepared in ultrahigh vacuum have been characterized in situ with pump-probe photoelectron spectroscopy using both synchrotron radiation and picosecond laser sources. Photoelectron spectra of singlet (S 1 ) and triplet (T 1 ) excitons overlap because of vibrational broadening in the photoemission final state. The spectra have been individually isolated in pp-C 60 with time-resolved methods and are split by 0.33 eV. Signals from pristine C 60 are weaker but are spectroscopically similar. The origin for exciton transitions for both C 60 and pp-C 60 is found to be properly located near the maximum of the highest occupied molecular orbital. Increasing excitation density favors T 1 production over S 1 such that, at high exciton concentrations, T 1 states predominate, even at times much shorter than the unimolecular intersystem crossing time, measured to be ϳ2.5 ns for pp-C 60 at 81 K. A weaker photoemission band located ϳ0.5 eV above S 1 is also observed and is attributed to charge carriers and/or charge-transfer excitons.