WAVE-FUNCTION OVERLAP EFFECTS IN THE COLLISIONAL EXCITATION OF NH3 BYSLOW MOLECULAR-IONS

Collisional excitation of ammonia from the ground 1A1 electronic state to various optically-allowed and dipole-forbidden states has been stu died in 1.8 keV collisions with H-2+, N2+ O2+ and CO2+ projectiles by energy loss spectrometry using a high-resolution ion translational ene rgy spectrometer. The collisional excitation cross section is found to be sensitively dependent on whether the projectile ion is of SIGMA or PI symmetry. This dependence is interpreted as a manifestation of wav efunction overlap effects involving the highest occupied molecular orb itals of the target and projectile ions. Results of concomitant theore tical calculations of overlap integrals for different orientations of each projectile-target system provide support for the wavefunction ove rlap picture,