Coaxial pulsed jet submillimeter spectra are reported for Ar:(HBr)-Br-79 and Ar:(HBr)-Br-81 transition frequencies measured with sub-kHz precision. This is confirmed by comparing combination frequency differences associated with DeltaF=+/-1 hyperfine components in the rovibrational transitions of the low frequency Sigma bending mode with corresponding sum frequencies of the rotational transitions in the ground state precisely measured with a pulsed-nozzle FT microwave spectrometer (1.5 kHz resolution, 200 Hz accuracy). Ground state molecular parameters evaluated using the submillimeter-wave and microwave techniques are demonstrated to have comparable accuracy. Furthermore, excited Sigma state molecular constants for the isotopic band origins of Ar:(HBr)-Br-79 and Ar:(HBr)-Br-81 at 329611.4284(10) and 329225.6778(10) MHz are shown to be determined with equivalent accuracy. (C) 2003 American Institute of Physics.