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

The collisional excitation of neutral ground state CH4 and CCl4 molecules is studied in 1.8 keV collisions with H-2(+), N-2(+), O-2(+) and CO2+ ions using ion high-resolution energy loss spectrometry. Excitation of CCl4 occurs in the case of collisions with projectile ions of Sigma 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 case of CH4 molecules, energy loss structure is weakly observed only in the case of collisions with H-2(+) ions. No energy loss is observed with any of the other projectile ions. The results are understood as manifestations of wavefunction overlap effects.