Ab Initio Calculation of 81Br Nuclear Quadrupole Resonance Transition Frequencies for Brominated Aromatics (Flame Retardants)

Abstract

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). Co...