Low frequency Raman spectra of K-(ET)&u(NCS)~ measured on a single crystal in a wide range of temperatures, above and below T,, allowed us to observe self-energy effects induced by the SC transition on the low-lying intermolecular phonons. Very low power density of the exciting laser field was used to avoid local heating of the irradiated volume. All the observed phonons lie above the BCS gap, and their frequencies increase below T,. The observed relative frequency shifts are consistent with those already reported for tc-(ET),Cu[N(CN),]Br [.5], but they are lower and, with the exception of the phonon at 65.8 cm, close to the experimental uncertainty. In general the intermolecular electron-phonon coupling appears weaker in K-(ET)&u(NCS)~ than in K- (ET)2Cu[N(CN),]Br. The low frequency Raman spectra of single crystals of K- (‘3C434Ss-ET)2C~(NCS)2 and K-(~H~-ET)~CU(NCS)~ measured at 10 and 2 K show significant isotopic shifts. Whereas for the 13Cj-Ss substituted compound the measured shifts can be explained as a normal mass effect, for the deuterated crystal the observed full isotopic shift is larger than that predicted by the product rule and justifies the suggested lattice softening induced by deuteration [16]. We thank P. Ingenito for useful discussion and technical help during the first part of this work and G. Marcolongo for technical help in the second part. Financial support by the Italian Ministry of University and the National Research Council is acknowledged. Work at Argonne Nat. Lab. is sponsored by the U.S. Department of Energy, Office of Basic Energy, Division of Materials Sciences,u nder contract W-31-109-ENG-38;