The high resolution FTIR spectrum of 1 3 CF 3 Br enriched by IR laser multiphoton dissociation, has been analysed in the region of the degenerate C F stretching mode. The Q branch maxima corresponding to the r Q K and p Q K sub-bands have been identified and assigned in the observed spectrum. The data have been fitted along with the ground state microwave measurements in a weighted least squares analysis to obtain molecular parameters for the ν 4 state. The ξ 4 value is estimated to be 0.77. The ν 4 band appears to be perturbed by l-type resonance, and it has been possible to determine the sign and also obtain an estimate for the l-type resonance parameter from band contour simulation.