Flip-flop reorientation

At the higher kinetic energy, of course the same forces act upon the molecule. But now the molecule is too fast to become significantly reoriented before it hits the repulsive wall of the potential at t = 50 fs. When the molecule reaches the surface in the tilted configuration, it starts quickly rotating in a flip-flop motion until the other end hits the surface. The molecule is then scattered back into the gas phase rotationally excited (which can not been infered from the panel at t = 300 fs). 

Exactly the same results were obtained with spin diffusion experiments performed at ZSM-39. Frequencies can be affected by spin diffusion between sites having different NMR parameters, when, for example, magnetization is transported through a solid by means of mutual spin "flip-flops" that can occur even in the absence of atomic or molecular motion. By monitoring the correlation among frequencies in the different dimensions of a multidimensional NMR experiment, it is possible to learn about the mechanisms and rates of reorientation and diffusion processes in solids (32). 

Membrane proteins show considerable mobility in the plane of the bilayer (lateral motion). There is no evidence that proteins migrate from one side of the bilayer to the other. The frequency of reorientation of lipid components (flip-flop migration) is extremely slow or nonexistent, for thermodynamic reasons. 

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