Reaction of CN–with F, Cl, O, andS Atoms: Attachment or Associative Detachment?

Highly correlated ab initio wavefunctions within the UCCSD(T)-F12approach have been used to map the potential energy surfaces (PESs)describing the reactivity of the CN–(X1Σ+) anion with neutral atoms presentin interstellar media (F, Cl, O, and S). With the H atom, for comparison,the reaction [CN–(1Σ+) + H(2S)] evolves along the PES of the X2Σ+electronic ground state of HCN–(or HNC–) until the crossing withthe X1Σ+electronic groundstate of HCN (or HNC), where electron detachment occurs. The processis rather similar to the two halogen atoms F and Cl, with some differencesdue to the larger electron affinity of the halogens, making possiblethe existence of ClCN–in a 2Σ+state. The reaction of CN–with O and Satoms proceeds via a multistep mechanism. The lowest electronic stateat long distance, the 3Π state arising from the [CN–(1Σ+) + O/S(3P)] reaction channel, does not correlate with the X1Σ+ground state of the XCN–anion (X = O or S). This 3Π state and its bentcomponents cross at medium RXC(RXN) distances the X1Σ+ground state of XCN–or XNC–, and at shorter distances the X2Π state of the neutral XCN or XNC where the extra electroncan detach. With both O and S atoms, it is shown that the spin–orbitcouplings can efficiently lead the [CN–(1Σ+) + O/S(3P)] reaction toward the stable X1Σ+ground state of XCN–and XNC–. [ABSTRACT FROM AUTHOR]