COLLISION-INDUCED ELECTRONIC EXCITATION OF CH-GAS ATOMS AND SOME DIATOMIC-MOLECULES( IONS BY IMPACT ON RARE)

Efficient excitation of the A (II)-I-1: and B (1) Delta electronic sta tes of CH+ ions was observed in collisions of CH+(X(1+)) with noble ga s atoms or diatomics (H-2, D-2, N-2, O-2, NO, CO) at kinetic energies up to 1 keV(lab). This process and the competing charge transfer formi ng CH(A(2) Delta) were investigated by spectral analysis of the subseq uent optical emission. In the energy range available, the excitation f unctions increase steadily with the collision energy. For systems wher e charge transfer excitation is negligible, the cross-section depends only moderately on the target gas species. Population of the CH+(B) st ate, which requires simultaneous excitation of two electrons in the co llision, proceeds with unexpectedly high efficiency. The energy depend ence here is somewhat different for rare gases and for diatomics. The total cross-sections for collisional formation of the electronically e xcited A and B states of CH+ are of the order of several Angstrom(2). From the ground singlet state only radiating singlet states of CH+ are collisionally populated, even when target gases are used for which th e spin-conservation rule would permit population of the CH+(b(3-)) sta te; the collisional transfer to this state does, however, occur from t he CH+(a(3)II) metastable state present in the projectile ion beam. Th e population of rotational states of CH+(A) corresponds to temperature s of 4000 K at 100 eV(lab) and 3000 K at 1000 eV(lab), independent of the target gas.