Vibrational Excitation of H₂, D₂, N₂ and O₂ by Li⁺ Impact in the Energy Range from 100 eV to 1200 eV

Cross sections for vibrational excitation of H 2 , D 2 , N 2 and O 2 by Li + impact are measured with an ion energy-loss spectrometer. The cross sections are obtained from relative height of the loss peaks in a spectrum. The absolute cross sections are obtained above a few hundred eV. The maximum values of the measured cross sections for v =0→1 excitation of H 2 , D 2 , N 2 and O 2 are 7.5×10 -18 cm 2 , 1.0×10 -17 cm 2 , 3.3×10 -18 cm 2 and 1.6×10 -17 cm 2 , respectively. For H 2 and D 2 , v =0→2 excitation is observed, while, it does not appear for N 2 and O 2 . The measured cross sections are compared with the first Born approximation assuming that the exctiation occurs only through polarization force. The contribution of the polarization force to the vibtational excitation of infrared active molecules is estimated.