Storage ring measurements of the dissociative recombination and excitationof the cyanogen ion CN+(X-1 Sigma(+) and a (3)Pi, nu=0)

Absolute cross sections and rate coefficients were measured for the dissoci ative recombination of CN+(X (1)Sigma(+) and a (3)Pi, nu=0) with electrons using the heavy ion storage-ring CRYRING ht Stockholm University. The a (3) Pi State that lies only 0.08 eV above the X (1)Sigma(+) ion groundstate is most certainly populated in the ion beam injected into CRYRING, as this is a long-lived excited state. Over the 1 meV-3 eV energy range that was inves tigated, two energy dependencies were found for the cross sections, namely E-105 below 0.1 eV and E-1.41 above 0.4 eV. The energy domain 0.1-0.3 eV ex hibits a resonant structure. Branching fractions over the final atomic prod uct states were determined using a position sensitive imaging detector. The rmal rate coefficients are deduced from the measurements and the efficiency displayed by the dissociative recombination mechanism is typical of that o f a diatomic ion (3.4 x 10(-7) cm(3) s(-1) at room temperature). Cross sect ions for the dissociative excitation process are also reported and their ma gnitude at the plateau are unusually large. This may be explained by the nu mber of potential curves which can be populated at moderate collision energ y (<10 eV) for the CN+ ion. (C) 1999 American Institute of Physics. [S0021- 9606(99)00201-9].