Driving High Threshold Chemical Reactions by Cluster-Surface Collisions: Molecular Dynamics Simulations for CH3I Clusters

Iodine bonding stabilizes iodomethane in MIDAS pesticide. Theoretical study of intermolecular interactions between iodomethane and chloropicrin

The results are reported of a theoretical study of iodomethane (H(3)C-I, 1) and chloropicrin (Cl(3)C-NO(2), 2), of the heterodimers 3-6 formed by aggregation of 1 and 2, and of their addition products 7 and 8 and their possible fragmentation reactions to 9-18. Mixtures of iodomethane and chloropicrin are not expected to show chemistry resulting from their reactions with each other. The structures and stabilities are discussed of the iodine-bonded molecular aggregates (IBMA) 3 and 4 and of the hydrogen- and iodine-bonded molecular aggregates (IHBMA) 5 and 6. The mixed aggregates 3-5 are bound on the free enthalpy surface relative to the homodimers of 1 and 2, and the IBMA structures 3 and 4 are most stable. This result suggests that the mixture of chloropicrin and iodomethane in the pesticide Midas is a good choice to reduce the volatility of iodomethane because of thermodynamically stabilizing iodine bonding.

Mechanical Simulation of the Pressure and the Relaxation to Thermal Equilibrium of a Hot and Dense Rare Gas Cluster

A cold atomic cluster can be very rapidly heated and compressed by a hypersonic impact at a hard surface. The impact can be simulated by computing a classical trajectory for the motion of the atoms. By suddenly confining the hot and dense cluster within a rigid container, it is possible to monitor the time evolution of the force acting on the faces of the container. It is found that the pressure computed this way very rapidly decays to a time-independent value. After a somewhat longer time, this value reproduces the value for the pressure computed as the sum of the kinetic and internal pressures. This agreement is expected for a system in equilibrium. These observations support the conclusion that there is a fast relaxation to thermal equilibrium in these essentially hard-sphere systems. The deviation from equilibrium is primarily due to the propagation of shock waves within the cluster. The equilibrium pressure can reach up to the megabar range.

Enhanced selectivity and yield in multichannel photodissociation reactions: Application to CH3I

We develop a method to improve the population transfer and final-channel control of multichannel photodissociation reactions. The method is applied to the photodissociation of methyl iodide, CH3(v)+I*(2P1/2)<--CH3I-->CH3(v)+I(2P3/2). Our method is based on simultaneously exciting many two-photon pathways that lead to the same final outcome, each proceeding via a different intermediate bound state. The selectivity of the final product state(s) is a result of coherently controlled interference between the quantum pathways. The improvement in the population transfer yield from the ground state to the selected dissociative channel(s) is made possible by executing the process in an adiabatic fashion.