Excitation of the four fundamental vibrations of CH₄by electron impact near threshold

Absolute differential elastic and vibrational excitation cross sections have been measured for CH 4 at 90° and from 0.1 to 1.5 eV, with the resolution of all four vibrational modes. Threshold peaks were observed in the excitation of the ν 1 , ν 3 and ν 4 modes, but not in the ν 2 mode. These results are in good agreement with the recent calculation of Nishimura and Gianturco ( 2002 J. Phys. B: At. Mol. Opt. Phys. 35 2873 ). No near-threshold structures were observed.