Force field calculations and reassigments of Raman and IR frequencies of pyrazine-N,N′-dioxide

Force field calculations have been carried out for the planar and non-planar modes of pyrazine-N,N′-O2 using the observed vibrational frequencies obtained from the IR and Raman spectral studies on pyrazine-N,N′-O2-h4 and pyrazine-N,N′-O2-d4 reported in the literature [D.A. Thornton, P.F.M. Verhoeven, G.M. Watkins, Herman O. Desseyn, Benjamin J. Van der Veken, Spectrochim. Acta 46A (1990) 1439]. The purpose of the present work is to determine force fields for the pyrazine-N,N′-O2 molecule and to present vibrational assignments for the observed IR and Raman frequencies to the fundamental modes, combination bands and overtones. The planar force field determined in the present case is expected to be better than that reported earlier [S. Szöke, G. Varsanyi, E. Baitz, Acta Chim. 53 (1967) 345] because of the inclusion of the observed frequencies due to pyrazine-N,N′-O2-d4 isotopomer. In addition, the non-planar force field for this molecule is reported for the first time.