Dissociative electron attachment to NO molecules and NO clusters

Dissociative electron attachment (DA) to single NO molecules and NO clusters is studied in two independent crossed electron--molecular-beam experiments with high-energy resolution including a kinetic-energy analysis of the O^- fragment ions. It is shown that the DA cross section exhibits a vertical onset near 7.45 eV that corresponds to the energetic threshold of the DA channel O^-(²P)+N*(²D). No indication of the ground-state channel O^-(²P)+N(⁴S) [O. J. Orient and A. Chutjian, Phys. Rev. Lett. 74, 501 (1995)] and no indication of long-lived N^- [H. Hiraoka, R. K. Nesbet, and L. W. Welsh, Jr., Phys. Rev. Lett. 29, 130 (1977)], as recently proposed, could be found. O^- formation from NO clusters shows the same features as from single NO molecules, indicating the same reaction mechanism, thus also excluding coupling to the ground-state DA channel clusters.