Excitational dissociation of C2H2molecules by impact of He+and Ar+ions in the energy range 30-300 eV

Optical emission from electronically excited fragments, H, CH and CH + , was observed in collisions of He + and Ar + ions with C 2 H 2 molecules in the energy range 30-300 eV. Emission from excited acetylene molecules or ions was not observed. Of these excited fragments, CH(B 2 Sigma - ) formed in He + collisions and CH + (B 1 Delta ) in He + and Ar + collisions show a linear dependence on the target pressure, indicating that they are produced in primary collision processes. On the other hand, CH(B 2 Sigma - ) formed in Ar + collisions and CH(A 2 Delta ) in He + and Ar + collisions show a quadratic dependence superimposed on a linear dependence on the target pressure. The pressure dependence of CH + (A 1 Pi ) ions formed in He + collisions shows a linear decrease, suggesting that a quenching process participates in the ion formation. Some reaction schemes are assumed in order to understand the ion production, using the basic concept that charge transfer between the projectile ion and the target is an essential process in the reactions.