Multiphoton ionization of ammonia clusters and the dissociation dynamics of protonated cluster ions

Abstract

Ammonia clusters, produced via supersonic expansion, are subjected to multiphoton ionization using a tunable pulsed laser. The products of ionization and subsequent dissociation processes are investigated using a time-of-flight mass spectrometer equipped with a reflectron (reflecting electric field). Cluster ions containing more than 65 ammonia molecules were formed via internal ion molecule reactions taking place within the initially ionized aggregate. The proton transfer reaction which ensues leads to substantial excess internal energy and subsequent cluster decomposition. Dissociation due to both collisional and unimolecular processes was identified in the field-free region. Studies of the dynamics of dissociation were made for species up to the protonated 16-mer; the loss of up to at least five monomer units following cluster ion formation was observed. Results of an investigation of the influence of laser fluence and the energy of the ionizing photons are also presented.

Dynamics and fragmentation of van der Waals clusters: (H2O)n, (CH3OH)n, and (NH3)n upon ionization by a 26.5eV soft x-ray laser

“…Third, based on studies of cluster ion metastability, the unimolecular decay occurs within a time window of 1 -15 s for these cluster ions. 11,48 This additionally holds true for methanol, 23 ammonia, 49 and acetone ͑Ref. 50͒ cluster ions.…”

The Formation of Clusters with Reactive Species Precursors to Aerosol Formation in the Ammonia—Sulfur Dioxide System

“…which occurs following ionization of the neutral ammonia clusters (Echt et al 1985). A peculiar feature is that the unprotonated species exhibit a normal smooth size distribution, which is peaked at cluster sizes containing three ammonia molecules as does the protonated ammonia distribution.…”

Formation and dissociation of protonated pyridine–methanol cluster ions at 355 and 266 nm

“…Suppose the mass of the parent ion is m p , with kinetic energy qU 0 , the mass of the daughter ion is m d with kinetic energy qU 0 m d am p , and both the parent and daughter ions enter the second ®eld, that is, U T`U0 m d am p`U0`UK , the¯ight time dierence to the detector is easily derived [17,18]:…”