Hyperfine structure of the A 3Π1 state of IBr

We have recorded saturated absorption spectra of the A 3-PI-1 (nu = 13) <-- X 1-SIGMA+ (nu' = 3) transition in (IBr)-I-125-Br-79. The hyperfine structures of the Q(50) and Q(60) lines at 776.4 and 777.8 nm have been measured and fitted. The theoretical intensities of the hyperfine components have been calculated and synthetic spectra generated, in good agreement with the experimental ones. The magnetic dipole and electric quadrupole hyperfine constants in the upper state 3-PI-1 (A') have been deduced: C(I) = 544.5 (17.6) MHz, C(Br) = 129.3 (14.4) MHz, eQq(I) = - 1470.4 (4.4) MHz and eQq(Br)= 570.1 (2.7) MHz.