COLLISIONAL EXCITATION OF CH4 AND CCL4 - WAVE-FUNCTION OVERLAP EFFECTS

The collisional excitation of neutral ground state CH4 and CCl4 molecu les is studied in 1.8 keV collisions with H-2(+), N-2(+), O-2(+) and C O2+ ions using ion high-resolution energy loss spectrometry. Excitatio n of CCl4 occurs in the case of collisions with projectile ions of Sig ma symmetry (H-2(+) and N-2(+)). No energy loss structure is observed when the projectile ions have II symmetry (O-2(+) and CO2+). In the ca se of CH4 molecules, energy loss structure is weakly observed only in the case of collisions with H-2(+) ions. No energy loss is observed wi th any of the other projectile ions. The results are understood as man ifestations of wavefunction overlap effects.