High-resolution (\left(0.003 \mathrm{~cm}^{-1}\right)) FTIR spectra of monoisotopic (\mathrm{H}{3} \mathrm{Si}^{79} \mathrm{Br}) have been studied in the (v{3}) and (v_{6}) regions near 430 and (630 \mathrm{~cm}^{-1}). We have fitted 2016 transitions for (v_{3}, 631) for (2 v_{3}) (\nu_{3}, 1987) for (\left(\nu_{3}+\nu_{6}\right)-\nu_{3}), and 3251 for (\nu_{6}), with standard deviations of the residuals of (0.206 \times) (10^{-3}, 0.378 \times 10^{-3}, 0.370 \times 10^{-3}), and (0.113 \times 10^{-3} \mathrm{~cm}^{-1}), respectively, taking into account the (l(2,2)) resonance within both the (v_{3}=v_{6}=1) and the (v_{6}=1) levels. In order to deduce precise ground state and excited state constants, we have also studied the (v=0) and (v_{6}=1) pure rotational transitions up to (J=53). Improved ground state parameters (B_{0}, D_{J}^{0}, D_{j K}^{0}, H_{J .}^{0}, H_{j K}^{0}). and (H_{K J}^{0}) were determined. The hot bands (2 \nu_{6}^{0}-\nu_{6}^{ \pm 1}) (only ({ }^{P} Q_{1}) and ({ }^{R} Q_{2}) series) and (2 \nu_{0}^{ \pm 2}-\nu_{6}^{ \pm 1}) have been assigned. Using high-resolution spectra of the fundamental band (v_{6}). of the overtone band (2 v_{6}^{72}) previously studied, and of the hot band (2 \nu_{6}^{ \pm 2}-v_{6}^{ \pm 1}), the ground state constants (A_{0}) and (D_{K}^{0}) for the (\mathrm{H}{3} \mathrm{Si}^{79} \mathrm{Br}) molecule have been determined. Ground state differences (\Delta(K, J)=F(K, J)-) (F(K-3, J)) were calculated for seven (K) values: (K=3,4,5,6,7,8), and 9 . By a least-squares fit of 370 such differences the following results ( in (\mathrm{cm}^{-1}) ) were obtained: (A{0}=(2.843016 \pm 0.000014)) and (D_{K}^{0}=(2.6665 \pm 0.0069) \times 10^{-5}). 1995 Academic Press. Inc