The polar tensor of allene was calculated from the infrared fundamental band intensities of C3H4 and C3D4. The ambiguities in the signs of the dipole moment derivatives with respect to their normal coordinates were resolved by comparison of tensor elements with ab initio calculations at the B3LYP, MP2(FC) and CCD(FC) levels with a 6/311 + + G(3d,3p) basis set. The results are similar to those previously obtained by Koga and co-workers except for the choice of an average of two sign combinations for the E symmetry elements. The values of the mean dipole moment derivatives for the sp and sp2 carbon atoms obtained in this work, 0.032 and -0.133 e, respectively, are in good agreement with the CCD(FC)/6-311 + + G(3d,3p), 0.061 and -0.128 e, and MP2(FC)/6-311 + + G(3d,3p), 0.072 and -0.153 e, theoretical results. The mean dipole moment derivatives are shown to be consistent with potential models relating 1s electron ionization energies and atomic charges.571369-75