REARRANGEMENTS OF AMMONIUM-NITRATE CLUSTER IONS WITH HIGH INTERNAL ENERGY

Sputtering of condensed-phase ammonium nitrate yields an extensive distribution of negative cluster ions of the form [(NH4NO3)(n)NO3](-), n greater than or equal to 3. Collision-induced dissociation of mass-selected cluster ions suggests that the first two members of the series, n = 1 and n = 2, are missing because the ions rearrange to lose one or more ammonia molecules. Gradient-corrected density-functional calculations show that NH4NO3 is strongly hydrogen bonded and that [(NH4NO3)NO3](-) has no hydrogen bonds, consistent with this ion rearranging to lose NH3 to form the strongly hydrogen-bonded ion [H(NO3)(2)](-).