Far- and mid-infrared photoacoustic spectra of tetracene, pentacene, perylene and pyrene

Far- and mid-infrared photoacoustic (PA) spectra of tetracene, pentacene, perylene and pyrene were acquired in this study. Far-infrared data were obtained at wavenumbers down to ∼80 cm−1 using large-amplitude phase modulation in a step-scan spectrometer; many previously unreported bands were observed in these spectra. For each compound, the fingerprint region of the mid-infrared spectrum (approximately 400–2000 cm−1) contained a large number of bands correlated with vibrations that are predicted to be either infrared or Raman active. In addition, numerous combination and overtone bands appeared in the mid-infrared spectra. This PA investigation provides the most detailed spectral data known for these four aromatic compounds.