Direct Dynamics Simulation of Dissociation of the [CH sub(3)--I--OH] super(-) Ion-Molecule Complex

Direct dynamics simulations were used to study dissociation of the [CH sub(3)--I--OH] super(-) complex ion, which was observed in a previous study of the OH super(-) + CH sub(3)I gas phase reaction ( J. Phys. Chem. A 2013, 117, 7162). Restricted B97-1 simulations were performed to study dissociation at 65, 75, and 100 kcal/mol and the [CH sub(3)--I--OH] super(-) ion dissociated exponentially, in accord with RRKM theory. For these energies the major dissociation products are CH sub(3)I + OH super(-), CH sub(2)I super(-) + H sub(2)O, and CH sub(3)OH + I super(-). Unrestricted B97-1 and restricted and unrestricted CAM-B3LYP simulations were also performed at 100 kcal/mol to compare with the restricted B97-1 results. The {CH sub(3)I + OH super(-)}:{CH sub(2)I super(-) + H sub(2)O}:{CH sub(3)OH + I super(-)} product ratio is 0.72:0.15:0.13, 0.81:0.05:0.14, 0.71:0.19:0.10, and 0.83:0.13:0.04 for the restricted B97-1, unrestricted B97-1, restricted CAM-B3LYP, and unrestricted CAM-B3LYP simulations, respectively. Other product channels found are CH sub(2) + I super(-) + H sub(2)O, CH sub(2) + I super(-)(H sub(2)O), CH sub(4) + IO super(-), CH sub(3) super(-) + IOH, and CH sub(3) + IOH super(-). The CH sub(3) super(-) + IOH singlet products are only given by the restricted B97-1 simulation and the lower energy CH sub(3) + IOH super(-) doublet products are only formed by the unrestricted B97-1 simulation. Also studied were the direct and indirect atomic-level mechanisms for forming CH sub(3)I + OH super(-), CH sub(2)I super(-) + H sub(2)O, and CH sub(3)OH + I super(-). The majority of CH sub(3)I + OH super(-) were formed through a direct mechanism. For both CH sub(2)I super(-) + H sub(2)O and CH sub(3)OH + I super(-), the direct mechanism is overall more important than the indirect mechanisms, with the roundabout like mechanism the most important indirect mechanism at high excitation energies. Mechanism comparisons between the B97-1 and CAM-B3LYP simulations showed that formation of the CH sub(3)OH---I super(-) complex is favored for the B97-1 simulations, whereas formation of the HO super(-)---HCH sub(2)I complex is favored for the CAM-B3LYP simulations. The unrestricted simulations give a higher percentage of indirect mechanisms than the restricted simulations. The possible role of the self-interaction error in the simulations is also discussed. The work presented here gives a detailed picture of the [CH sub(3)--I--OH] super(-) dissociation dynamics and is very im