Spectral hole-burning of tetracene and tetracene-argon complexes in a supersonic jet

Abstract

The fluorescence excitation spectra of the tetracene mol. and the van der Waals clusters tetracene.Arn with n = 1, 2, 3 cooled in a supersonic free jet expansion were obtained with a spectral hole-burning technique. The supersonic beam contained a mixt. of clusters up to n = 7. The influence of clustering on the intramol. vibrations of tetracene up to a vibrational excess energy of 1250 cm-1 was very small. For the three smallest (n = 1 - 3) clusters a low-frequency vibration with a wavenumber of about 40 cm-1 was found and assigned to the motion of the Ar atom perpendicular to the mol. plane. A vibration with a wavenumber of 8 cm-1 corresponding to the motion parallel to the plane of the tetracene mol. was distinctly obsd. only in the cluster contg. a single Ar atom. Weak lines due to the minor species can be assigned unambiguously even if they are strongly overlapped by lines of another species.