[en] The azimuthal-angle distribution of Ni⁺ ions ejected from Ni(111) by bombardment with 2.0-keV Ar⁺ has been measured as a function of temperature in the range 263--500 K. The results show that the anisotropy of the Ni⁺ azimuthal-angle distribution is nearly independent of temperature up to 300 K, but decreases rapidly as the temperature increases from 320 to 380 K. The Ni⁺ azimuthal anisotropy appears to be nearly independent of temperature above ∼390 K. The experimental results are well described by molecular-dynamics simulations that account for thermal vibrations in the top atomic Ni layer. Comparison of the experimental results with the results of molecular-dynamics simulations is used in combination with the Debye model, to reveal information about the magnitude of vibrational displacements in the top atomic layer