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Mid-infrared characterization of the clusters in the neighborhood of the “magic” number
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Image of FIG. 1.
FIG. 1.

Time-of-flight mass spectrum of , for and , obtained by electron impact ionization of a supersonic expansion containing a mixture of water and argon followed by entrainment of ammonia vapor. Note, the labeled peaks correspond to the mixed species for resulting in the clusters and clearly show the “magic number” at .

Image of FIG. 2.
FIG. 2.

Comparison of the vibrational predissociation spectra of the (a) and (b) “magic number” clusters in the region.

Image of FIG. 3.
FIG. 3.

Vibrational spectra of , for , in the region highlighting the evolution of the sharp bands (labeled ) arising from dangling hydrogen atoms. The outer two bands labeled and correspond to the symmetric and asymmetric stretches of the water molecules in a single acceptor motif, while the remaining features labeled and arise from water molecules in AAD and AD motifs. See discussion within the text for more details.

Image of FIG. 4.
FIG. 4.

Isomers of and optimized at the level of theory. The group is indicated by the gray circle in each cluster.

Image of FIG. 5.
FIG. 5.

Comparison of the calculated and measured vibrational spectra in the free OH stretch region of (a) and (b) . The calculated spectra are reported for isomers 19A and 20A and were generated from calculations, with the harmonic frequencies being scaled by 0.9735 and the individual transitions being given Lorentzian linewidths of .

Image of FIG. 6.
FIG. 6.

Calculated vibrational spectrum of isomer 20A of from . The calculated harmonic frequencies have been scaled by 0.9735 and the individuals transitions have been given Lorentzian linewidths of .


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Table I.

Formation energies (kcal/mol) for selected isomers of and .a

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Table II.

Calculated harmonic frequencies for the NH stretch for selected isomers of and clusters and for and .a


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Mid-infrared characterization of the NH4+∙(H2O)n clusters in the neighborhood of the n=20 “magic” number