Raman spectra and calculated vibrational frequencies of size-selected C-16, C-18, and C-20 clusters

The surface plasmon polariton-enhanced Raman spectra of size-selected C-16, C-18 and C-20 clusters isolated in nitrogen matrices are presented along w ith the calculated vibrational frequencies for the ring and linear chain is omers. The Raman spectra, recorded at a range of excitation wavelengths fro m 457.9 to 670 nm, show strong resonance enhancement for the three clusters . The calculated vibrational frequencies for ring and linear chain isomers and the cage and bowl structures for C-20 are compared to the experimental frequencies. Systematic shifts in the series of peaks in the 200 cm(-1) reg ion for C-16, C-18, and C-20 suggest that the observed isomers have the sam e geometry, thereby ruling out the bowl and cage isomers for C-20 The measu red spectra appear to be most consistent with the linear chain isomer. This high-energy isomer may be produced during neutralization of the deposited cluster ions. (C) 1998 American Institute: of Physics. [S0021-9606(98)02346 -0].