INVESTIGATION OF THE PURE ROTATIONAL SPECTRUM OF MAGNESIUM MONOBROMIDE BY FOURIER-TRANSFORM MICROWAVE SPECTROSCOPY

The pure rotational spectrum of the free radical MgBr has been measure d in its (2) Sigma(+) ground electronic state by Fourier transform mic rowave spectroscopy. Transitions have been observed for both (MgBr)-Mg -24-Br-79 and (MgBr)-Mg-24-Br-81 in the v = 0 and v = 1 vibrational st ates. Rotational and centrifugal distortion constants have been determ ined for each isotopomer in each vibrational state. Equilibrium rotati onal constants have been calculated and an accurate equilibrium bond l ength has been determined. Spin-rotation constants, for both the unpai red electron and the bromine nuclei, have been calculated along with m agnetic and nuclear quadrupole hyperfine constants for the bromine nuc lei. From these constants, the electronic structure of MgBr has been i nvestigated and comparisons have been made to similar compounds. The u npaired electron spin density on the bromine nucleus has been found to be very small, suggesting that this is a very ionic compound. However , the Mg-Br bond has been found to have more covalent character than t he bond in other alkaline earth monobromides. (C) 1997 American Instit ute of Physics. [S0021-9606(97)02046-1].