Cr. Harwell et al., Ab initio calculation of Br-18 nuclear quadrupole resonance transition frequencies for brominated aromatics (flame retardants), J PHYS CH A, 103(40), 1999, pp. 8088-8092
Brominated aromatics, used extensively as flame retardants, have been studi
ed with Br-81 nuclear quadrupole resonance (NQR) spectroscopy. NQR requires
lengthy frequency searches because Br-81 NQR transition frequencies in bro
minated aromatics are spread over a wide (40 MHz) range. We investigate the
ability of ab initio calculations to narrow this search range by predictin
g Br-81 NQR transition frequencies for a series of brominated aromatics, us
ing restricted Hartree-Fock (RHF) and Becke's three-parameter Lee-Yang-Parr
density functional theory hybrid method (B3LYP). Basis sets used are of do
uble and triple-zeta quality with varying degrees of polarization included
on bromine. Geometries are the isolated molecules, with coordinates optimiz
ed for lowest energy. The results of calculations for nine simple brominate
d aromatics are fit against experimental frequencies and the fit is subsequ
ently used to predict frequencies of larger, two-ring brominated aromatics
(one is sold commercially as a flame retardant). Comparison to experiment s
hows the accuracy of this approach to be approximately 5 MHz, reflecting a
significant, 8-fold decrease in the spectral range to be searched by experi
ment.