Energetics of gas phase proton solvation by NH3

Abstract

The absolute proton affinity of NH3 (203.6±1.3 kcal/mole at 298 K) and the proton solvation energies by more than one NH3 have been determined by the molecular beam–photoionization method. In addition, the NH3+–NH3 interaction energy (0.79±0.05 eV) has been measured by photoionization of the neutral van der Waals dimer. These experiments have shown that photoionization of van der Waals clusters is a very powerful method for determining the energetics of gas phase proton solvation.

Ultrafast fragmentation and ionisation dynamics of ammonia clusters

“…We take this to be a strong indication that state 3 is indeed the postulated internally protonated, excited state (NH3),-3NHzNH4 which is stabilised in the picosecond time domain by NH3 loss or decays to a large extent into the X channel, hence the weakness of the resulting homogeneous cluster ion signals (NH3) +_ 1 = (NH3),-3NHzNH~ -. 4) We assume that at most only one fragmentation step occurs in the neutral system on the picosecond timescale available before ionisation. Due to the reduced energy content after the reaction 3 --+ 5 we do not expect state 5,…”

“…ll) as a function of time for the case of (NH3)3 as parent cluster. The population of state 2 is given by the left hand ordinate while the right hand ordinate represents the population multiplied by P~v.h (branching ratio times detection probability) as used to fit the NH3NH~-data (3,4) and the (NH3)~ signal (5) with P33 = P33 b23,/344 =-fi44 b24 and Pss = ¢55s b3s b23 so that we may solve this set of coupled equations together with the optical Bloch equations for just two free parameters, T20 and T30. The results are then convoluted with the time dependence of the probe pulse intensity to account for the incoherent ionisation process and we obtain as contribution to the observed signal:…”

“…[1,2] and references quoted there) and experimental studies such as thermochemical determinations of binding energies [3], photon [4][5][6][7][8] and electron impact [9] ionisation. These earlier studies were *Also at: Fachbereich Physik, Freie Universitfit Berlin, Berlin, Germany focused mainly on the energetics and structure of the clusters.…”

The role of charge and proton transfer in fragmentation of hydrogen-bonded nanosystems: the breakup of ammonia clusters upon single photon multi-ionization

“…This transfer is exothermic (about 0,74 eV 20,22 ) and happens on a femtosecond timescale. [23][24][25] The deprotonated fragment often evaporates swiftly from the cluster, but a small fraction can remain in the same cluster as the protonated fragment.…”

“…Pioneering work has established that charge transfer along the hydrogen bond forms an effective path along which a proton (charge) can 'hop' between molecular units, following the reac-1-9 | 1 4 2 6 4 4 3 4 6 0 4 7 7 4 9 4 5 1 1 2 5 2 6 2 7 2 8 2 9 3 0 1 2 3 4 5 6 7 8 9 1 0 1 1 1 2 1 3 1 4 1 5 1 6 1 7 1 8 3 5 5 2 6 9 8 6 1 0 3 1 2 0 1 3 7 1 5 4 1 7 1 1 8 8 2 0 5 2 2 2 2 3 9 2 5 6 2 7 3 2 9 0 1 4 1 5 1 6 1 7 tion: [19][20][21][22] …”