Non-scrambling of hydrogen in NH 4 + (H 2 O) 3 clusters.

We have measured the metastable decay of protonated, ammonia-doped, deuterated water clusters produced in an electrospray source, d n -NH 4 + (H 2 O) 3 , n = 0-6. The mass spectra show a very strong odd-even effect, consistent with a low degree of scrambling of the hydrogen bound to water and to the ammonia. The relative evaporation rate constant for light water was almost twice the one for heavy water, with the rate for mixed protium-deuterium water molecule intermediate between these two values.