The high resolution FTIR spectrum of 13CF3Br enriched by IR laser mult
iphoton dissociation, has been analysed in the region of the degenerat
e 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 obser
ved spectrum. The data have been fitted along with the ground state mi
crowave measurements in a weighted least squares analysis to obtain mo
lecular parameters for the nu4 state. The zeta4 value is estimated to
be 0.77. The nu4 band appears to be perturbed by l-type resonance, and
it has been possible to determine the sign and also obtain an estimat
e for the l-type resonance parameter from band contour simulation.