A quantum mechanical potential energy curve (IPA potential) of the iodine B 3Π+ou state was determined. The analysis of the outer branch of this potential (which encompasses 99.96 % of the depth well from υ = 0 to υ = 80) was carried out by means of the multipole expansion of the interaction energies truncated up to the C10/R10 v term ; the exchange energies Vex(R) being neglected and hyperfine effects ignored. In the analysed region (from 7 to 12 A) the estimated Vex(R) are small and may even be cancelled by the contribution of the neglected term C12 /R12υ; moreover, the dissociation limit energy De and the Cn coefficients are not depending of the number of turning points considered. The values of De and Cn are respectively found to be equal to De = 4 381.2492 ± 0.001 cm-1 C5 = 3.161 (33) × 105cm-1 Å 5 C6 = 1.506(43) × 106 cm-1 Å6 C8 = 0.248(14) × 108 cm-1 Å8 C10 ≤ 0.042(3) × 1010 cm-1 Å10, the quoted uncertainties being those resulting from fits using the calculated IPA potential