A band system of the (\mathrm{MnF}) molecule at (832 \mathrm{~nm}) representing the (b^{5} \Pi_{i}-a^{5} \Sigma^{+})transition has been studied at low temperature by laser-induced fluorescence in a supersonic jet and at high temperature in a hollow cathode discharge by Fourier transform spectroscopy. Most of the 46 assigned branches and other features in the low-temperature recording are shown to arise from satellite transitions. A set of molecular parameters has been derived for the (b^{5} \Pi), state. The locations of the origins of the individual components of the (b^{s} \Pi_{i}) state show anomalous behavior which is interpreted as arising from an interaction with the lower lying, hitherto unidentified ({ }^{5} \Delta_{i}) state derived from the ({ }^{5} D) term of the (3 d^{6}) configuration of the (\mathrm{Mn}^{+})ion. The magnitude and sign of the first-order spin-orbit constant indicates that the (b^{5} \Pi_{i}) state is derived from the ({ }^{5} D) term of the (3 d^{6}) configuration of the (\mathrm{Mn}^{+})ion. Observed linewidths are interpreted in terms of different hyperfine widths of the different spin components of (a^{5} \Sigma^{+})and (b^{5} \Pi_{i}). (C) 1994 Academic Press, Inc.