High Resolution IR Spectroscopy of the C–H Stretch Bands of Benzene Monomer and Dimer in Helium Nanodroplets

Abstract

Abstract The IR spectrum of benzene and benzene dimer embedded in superfluid helium droplets in the region of the C–H stretch vibration (3000–3110 cm-1) was observed. By analyzing the pressure dependence of the spectra it was possible to assign these spectra to benzene monomer and dimer. Based on a comparison of the observed position of the dimer bands to experimental bands recorded in the gas phase and to theoretical frequency predictions the authors assign these to the tilted T-shaped benzene dimer structure. None of the other two possible structures (PD or PTS) were found. The above assignment is firm. For the monomer, we find in helium nanodroplets a splitting of the ν 8+ν 19 combination band observed in the gas phase. We assign this to an additional Fermi resonance which is caused by the matrix shift in helium nanodroplets.