Microwave spectroscopic study of the BBr molecule

The reactive species BBr was produced by the glow discharge of the BBr 3 vapor in a free space cell. Rotational spectra of the four isotopic species were observed between 117 and 480 GHz. For lower rotational transitions the hyperfine structure owing to the bromine nucleus has been observed, and from its analysis the nuclear quadrupole interaction constant has been determined. The breakdown of the Born-Oppenheimer approximation for the rotational constant was recognized and the relevant parameters were determined.