a development attracting attention in 2008 concerns a sn2 roundabout mechanism observed in a gas-phase reaction between chloride ions and methyl iodide with a special technique called "crossed molecular beam imaging". when the chloride ions have sufficient velocity, the energy of the resulting iodide ions after the collision is much lower than expected, and it is theorized that energy is lost as a result of a full roundabout of the methyl group around the iodine atom before the actual displacement takes place.