Brominated aromatics, used extensively as flame retardants, have been studied with 81Br nuclear quadrupole
resonance (NQR) spectroscopy. NQR requires lengthy frequency searches because 81Br NQR transition
frequencies in brominated aromatics are spread over a wide (40 MHz) range. We investigate the ability of ab
initio calculations to narrow this search range by predicting 81Br NQR transition frequencies for a series of
brominated aromatics, using restricted Hartree−Fock (RHF) and Becke's three-parameter Lee−Yang−Parr
density functional theory hybrid method (B3LYP). Basis sets used are of double and triple-ζ quality with
varying degrees of polarization included on bromine. Geometries are the isolated molecules, with coordinates
optimized for lowest energy. The results of calculations for nine simple brominated aromatics are fit against
experimental frequencies and the fit is subsequently used to predict frequencies of larger, two-ring brominated
aromatics (one is sold commercially as a flame retardant). Comparison to experiment shows the accuracy of
this approach to be approximately 5 MHz, reflecting a significant, 8-fold decrease in the spectral range to be
searched by experiment.
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