GROUND-STATE MOLECULAR PAIR FORMATION IN AMORPHOUS ANTHRACENE DEPOSITED ONTO A METAL-SUBSTRATE AT INTERMEDIATE TEMPERATURES

Anthracene films deposited onto cold metal substrates in vacuum were studied by Raman spectroscopy. They were found to be amorphous but weakly indicated the formation of some molecular pairs with close contacts when the substrate temperature at deposition was set at around 120 K. Fluorescence measurements showed that these molecular pairs in the electronic ground state are the source of the previously reported excimer fluorescence. This local ordering in amorphous anthracene seems to inhibit the system from crystallization which starts at around 200 K if the sample is highly disordered.