Journal of Chemical Physics, Vol.110, No.11, 5159-5173, 1999
Solvation of cyclopentadienyl and substituted cyclopentadienyl radicals in small clusters. I. Nonpolar solvents
Cyclopentadienyl (cpd), methylcpd (mcpd), fluorocpd (Fcpd), and cyanocpd (CNcpd) are generated photolytically, cooled in a supersonic expansion, and clustered with nonpolar solvents. The solvents employed are Ar, N-2,CH4,CF4, and C2F6. These radicals and their clusters are studied by a number of laser spectroscopic techniques: Fluorescence excitation (FE), hole burning (HB), and mass resolved excitation (MRE) spectroscopies, and excited state lifetime studies. The radical D-1 <-- D-0 transition is observed for these systems: The radical to cluster spectroscopic shifts for the clusters are quite large, typically 4 to 5 times those found for stable aromatic species and other radicals. Calculations of cluster structure are carried out for these systems using parameterized potential energy functions. Cluster geometries are similar for all clusters with the solvent placed over the cpd ring and the center-of-mass of the solvent displaced toward the substituent. The calculated cluster spectroscopic shifts are in reasonable agreement with the observed ones for N-2 and CF4 with all radicals, but not for C-2 F-6 with the radicals. The Xcpd/Ar data are sacrificed to generate excited state potential parameters for these systems. CH4 is suggested to react with all but the CNcpd radical and may begin to react even with CNcpd. van der Waals vibrations are calculated for these clusters in the harmonic approximation for both D-1 and D-0 electronic states; calculated van der Waals vibrational energies are employed to assign major cluster vibronic features in the observed spectra.
Keywords:DER-WAALS COMPLEXES;LASER-INDUCED FLUORESCENCE;RESOLVEDELECTRONIC-SPECTRUM;2P3S RYDBERG STATE;VANDERWAALS COMPLEXES;RARE-GASES;VIBRATIONAL DYNAMICS;NONADIABATIC PREDISSOCIATION;MOLECULAR CLUSTERS;VIBRONIC STRUCTURE