Dissociative electron attachment to CO and NO: the O− production threshold revisited

Dissociative electron attachment (DA) to CO and NO has been investigated with a new crossed beams apparatus using a hemispherical electron monochromator. The DA cross-section curve for CO shows a vertical onset at the threshold (9.63 eV) of the lowest possible DA channel O−(2P)+C(3P). It is also possible to see a distinct onset (and peak) at the thermochemical threshold for the first excited channel O−(2P)+C*(1D). The DA cross-section curve for NO previous exhibits a vertical onset at the threshold (7.47 eV) for the first excited DA channel O−(2P)+N*(2D) and below 7.47 eV no signal for the energetically lower ground-state channel O−(2P)+N(4S) with a thermochemical threshold of 5.07 eV. We observe above ∼8.5 eV the occurrence of anions associated with the second excited DA channel O−(2P)+N*(2P).