Relative integral cross sections for rotational excitation of CO in collisions with He were measured at energies of 72 and 89 meV. The cross sections are sensitive to anisotropy in the repulsive wall of the He-CO interaction. The experiments were done in crossed molecular beams with resonance enhanced multiphoton ionization detection. The observed cross sections display interference structure at low ⌬ j, despite the average over the initial CO rotational distribution. At higher ⌬ j, the cross

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... ctions decrease smoothly. The results are compared with cross sections calculated from two high quality potential energy surfaces for the He-CO interaction. The ab initio SAPT surface of Heijmen et al. ͓J. Chem. Phys. 107, 9921 ͑1997͔͒ agrees with the data better than the XC͑fit͒ surface of Le Roy et al. ͓Farad. Disc. 97, 81 ͑1994͔͒.