Elastic and inelastic. alpha. scattering on sup 36 Ar at E sub. alpha. =40, 48, and 54 MeV

Differential cross sections for elastic and inelastic {alpha}- scattering on {sup 36}Ar have been measured at 40, 48, and 54 MeV. The data have been analyzed in the coupled-channel approach using double-folded optical {alpha}-{sup 36}Ar potentials considering the model of the symmetric rotator and the harmonic vibrator. The octupole transition probability deduced in the harmonic-vibrator model is almost identical to the value obtained from electromagnetic probes. In the symmetric-rotator model only the choice of negative {beta}{sub 2} and {beta}{sub 4} deformation parameters results in consistent fits to the data at all incident energies. This unambiguously proves the oblate shape of {sup 36}Ar. The volume integrals and rms radii of the extracted optical potentials fit well into the systematics obtained for lighter {ital sd}-shell nuclei.