EQUILIBRIUM NUCLEAR-QUADRUPOLE COUPLING-CONSTANTS FROM THE ROTATIONALSPECTRUM OF BRCL - A SOURCE OF THE ELECTRIC QUADRUPOLE-MOMENT RATIOS Q(BR-79) Q(BR-81) AND Q(CL-35)/Q(CL-37)/

The nuclear hyperfine structure in the J=1<--0 transitions of the four isotopomers (BrCl)-Br-79-Cl-35, (BrCl)-Br-79-Cl-37, (BrCl)-Br-81-Cl-3 5 and (BrCl)-Br-81-Cl-37 has been observed in the vibrational states n u=0 and nu=1 by pulsed-nozzle, Fourier-transform microwave spectroscop y. Accurate values of the nuclear quadrupole coupling constants X(aa)( nu) (X), where X=Br or Cl, and the spin-rotation coupling constants M( bb)(nu) (X) are determined from the spectra. Equilibrium values X(aa)( e)(X) and M(bb)(e)(Br) are derived from the vibrationally averaged qua ntities and the former lead to precise isotopic ratios, Q(Br-79)/Q(Br- 81)=1.197048(3) and Q(Cl-35)/Q(Cl-37)=1.26889(3) for the nuclear elect ric quadrupole moments.