Proton transfer in 1,4-dioxane/ammonia hydrogen bond clusters

The photoionization-dissociation patterns of neutral clusters M(NH3)(n) (M = 1,4-dioxane) were studied by synchrotron radiation and TOF mass spectrometry. The observed major product cations are protonated cluster ions M(NH3)(n)H+, and the intensities of unprotonated cluster ions M(NH3)(n)(+) are much lower. This phenomenon was also investigated with ab initio MO theory. The calculated results show that the neutral cluster M(NH3)(2) is vertically ionized into the unstable cation M-NH3-N+*H-3 and the cation easily undergoes a fast barrierless proton-transfer process to form the stable intermediate M(NH3)H+-NH2, then the intermediate dissociates into a protonated ionic cluster M(NH3)H+ and a radical NH2.