Collisional excitation of CH₄ and CCl₄: wavefunction overlap effects

Abstract

The collisional excitation of neutral ground state CH₄ and CCl₄ molecules is studied in 1.8 keV collisions with H₂⁺, N₂⁺, O₂⁺ and CO₂⁺ ions using ion high-resolution energy loss spectrometry. Excitation of CCl₄ occurs in the case of collisions with projectile ions of Σ symmetry (HH₂⁺ and NH₂⁺). No energy loss structure is observed when the projectile ions have ∏ symmetry (OH₂⁺ and COH₂⁺). In the case of CH₄ molecules, energy loss structure is weakly observed only in the case of collisions with H₂⁺ ions. No energy loss is observed with any of the other projectile ions. The results are understood as manifestations of wavefunction overlap effects.