Normal Mode Analysis of Vibrations of Jet-Cooled Acridine Dimer

I. Deperasińska and J. Prochorow Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warsaw, Poland

Received: November 19, 1999

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The analysis of normal modes of vibrations was performed for acridine dimer, which has been recently observed and identified by laser-induced emission spectroscopy under conditions of jet-cooling in a supersonic helium expansion. The frequencies and the forms of normal vibrations, computed with the use of the semi-empirical PM3 method are classifying all vibrations of acridine dimer into two distinct categories of inter- and intramolecular vibrations. There are six low-frequency intermolecular normal vibrations which are characterizing relative movements of two acridine moieties in the dimer and at least two of them have vibrational frequencies which are close to the frequencies of vibronic bands observed in the fluorescence excitation spectrum of the dimer. The intramolecular normal vibrations of the dimer very strictly correspond to the normal vibrations of acridine molecule (with a minor modification of the vibrational frequencies due to the splitting in the dimer). Furthermore, the intramolecular vibrations of acridine dimer, as well as the vibrations of acridine molecule are in good agreement with available experimental data (either IR and Raman spectra of acridine or fluorescence excitation spectrum of acridine dimer in supersonic jet). The results of the present analysis are very clearly supporting the previous conclusions concerning the ground-state equilibrium structure of acridine dimer formed under jet-cooling conditions.

DOI: 10.12693/APhysPolA.97.285 PACS numbers: 33.20.Tp