Impact induced vibrational excitation in surface scattering of hyperthermal neutral C-60 molecule

A mass-spectrometry based method for measuring the average vibrational energy (vibrational thermometry) of large and hot polyatomic molecules is presented. The method is applied to C-60 inelastically scattered off nickel with impact energies of 10-50 eV. Both the vibrational cooling effect on the supersonically expanded C-60 and the collisional excitation upon surface impact are measured within an experimental accuracy of +/-0.25 eV. Under nearly normal beam incidence conditions and impact energy of 33.0 eV (out of which 30.6 eV are in the normal energy component), vibrational excitation was found to be below similar to 2% of the impact energy, showing that the recoiled C-60 is nearly nondeformed at these collision energies. This value is much lower than estimated before for higher energies C-60(+) ion surface scattering. The implication of this result in relation with the low energy scattering dynamics of C-60 is discussed. (C) 1997 American Institute of Physics.