Collisional excitation of CH<SUB>4</SUB> and CCl<SUB>4</SUB>: wavefunction overlap effects

The collisional excitation of neutral ground state CH<SUB>4</SUB> and CCl<SUB>4</SUB> molecules is studied in 1.8 keV collisions with H<SUB>2</SUB><SUP>+</SUP>, N<SUB>2</SUB><SUP>+</SUP>, O<SUB>2</SUB><SUP>+</SUP> and CO<SUB>2</SUB><SUP>+</SUP> ions using ion high-resolution energy loss spectrometry. Excitation of CCl<SUB>4</SUB> occurs in the case of collisions with projectile ions of Σ symmetry (HH<SUB>2</SUB><SUP>+</SUP> and NH<SUB>2</SUB><SUP>+</SUP>). No energy loss structure is observed when the projectile ions have ∏ symmetry (OH<SUB>2</SUB><SUP>+</SUP> and COH<SUB>2</SUB><SUP>+</SUP>). In the case of CH<SUB>4</SUB> molecules, energy loss structure is weakly observed only in the case of collisions with H<SUB>2</SUB><SUP>+</SUP> ions. No energy loss is observed with any of the other projectile ions. The results are understood as manifestations of wavefunction overlap effects