The lowest frequency Sigma bending vibration of Ar:HBr has been recorded using frequency and phase stabilized Fast Scan Submillimeter Spectroscopic Technique (FASSST) coaxially with a supersonic jet. The fitted band origin was nu(0) = 329611.4482(16) MHz, the excited stated rotational constant was B = 1236.41359(22) MHz, the distortion constants were D-J = 0.0124740(36) MHz and H-J = -2.503(17) x 10(-6) MHz and the quadrupole constants were chi(aa) = 260.9552(79) MHz and D-chi = -0.03174(35) MHz for Ar:(HBr)-Br-79. Corresponding values have also been determined for the Ar:(HBr)-Br-81 isotopomer. chi(aa) and D-chi are compared with values predicted from a recently determined morphed potential of Ar:HBr. (C) 2003 Elsevier Science B.V. All rights reserved.