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

Abstract

The fluorescence excitation spectra of the tetracene molecule and the van der Waals clusters tetracene·Ar itn with n=1,2,3, cooled in a supersonic free jet expansion have been obtained with a spectral hole-burning technique. The supersonic beam contained a mixture of clusters up to n=7. The influence on the intramolecular vibrations of tetracene up to vibrational excess energy of 1250 cm −1 was found to be very small. For the three smallest ( n=1–3) clusters a low-frequency vibration with a wavenumber of about 40 cm − was found and assigned to the motion of the Ar atom perpendicular to the molecular plane. A vibration with a wavenumber of 8 cm − corresponding to the motion parallel to the plane of the tetracene molecule was distincly observed only in the cluster containing a single Ar atom. It is shown that weak lines due to the minor species can be assigned unambiguously even if they are strongly overlapped by lines of another species.