Spin-forbidden F ϩ transfer between 2 NF ϩ and CO: a computational study on the detailed mechanistic aspects

Abstract The detailed mechanistic aspects of the ion-molecule reaction between 2 NF ϩ and CO with formation of 1 FCO ϩ and 4 N have been investigated by using density functional theory and ab initio calculations. We have first located on the ground doublet and quartet B3LYP/6-311ϩG(d) (N,F,C,O) ϩ potential energy surfaces the various energy minima and transition structures involved in this process, and subsequently located the minimum energy points lying on the B3LYP/6-311ϩG(d) line of intersection between the two surfaces by using a recently described steepest descent-based method [Theor. Chem. Acc. 99 (1998) 95]. The obtained results indicate that this "spin-forbidden" reaction is a viable process in the gas phase, and could occur by two alternative mechanisms. The first one consists of the formation of the ( 2 NF ϩ /CO) adduct 1 on the doublet (N,F,C,O) ϩ surface, which subsequently undergoes the spin-forbidden isomerization into the loosely bound adduct ( 4 N/FCO ϩ ) adduct 5 on the quartet surface via a 1,2 fluorine shift from nitrogen to carbon. Isomer 5 undergoes in turn the barrier-free dissociation into the 4 N and FCO ϩ reaction products. The second conceivable mechanistic route consists of the formation of the adduct 1 and its isomerization into the ( 2 N/FCO ϩ ) adduct 7 via an adiabatic process. The eventual spin-forbidden formation of isomer 5 from isomer 7 occurs by a nonadiabatic 1,2 fluorine shift from nitrogen to carbon. (Int J Mass Spectrom 201 (2000) 151-160

On the proton-bound noble gas dimers (Ng-H-Ng)+ and (Ng-H-Ng')+ (Ng, Ng'= He-Xe): relationships between structure, stability, and bonding character

The structure, stability, and bonding character of fifteen (Ng-H-Ng)+ and (Ng-H-Ng')+ (Ng, Ng' = He-Xe) compounds were explored by theoretical calculations performed at the coupled cluster level of theory. The nature of the stabilizing interactions was, in particular, assayed using a method recently proposed by the authors to classify the chemical bonds involving the noble-gas atoms. The bond distances and dissociation energies of the investigated ions fall in rather large intervals, and follow regular periodic trends, clearly referable to the difference between the proton affinity (PA) of the various Ng and Ng'. These variations are nicely correlated with the bonding situation of the (Ng-H-Ng)+ and (Ng-H-Ng')+. The Ng-H and Ng'-H contacts range, in fact, between strong covalent bonds to weak, non-covalent interactions, and their regular variability clearly illustrates the peculiar capability of the noble gases to undergo interactions covering the entire spectrum of the chemical bond.3n