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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 22, Number 6
BKCSDE 22(6)
June 20, 2001 

Ab initio Study on Structures, Energies and Vibrations of Methylammonium-(water)n (n=1-3) Complexes
Kwang-Yon Kim, Ung-In Cho, Doo Wan Boo
Ab initio, Solvation, Hydrogen bond cooperativity, Many-body interaction.
The B3LYP/6-31+G(d) calculations on the structures, the hydration energies, the thermodynamic functions, and the vibrations of various isomers of CH3NH3+ (H2O)n (n=1, 2, 3) have been performed. Results indicate that not only the direct charge-dipole two-body interactions, but also the three-body interactions involving water-water hydrogen bonding and indirect charge-dipole interactions play significant roles in determining the overall structures and relative stabilities of isomers. Particularly, the hydrogen bond cooperativity plays a critical role in stabilizing the cyclic isomer vs. tripod isomer for n=3. The calculated thermodynamic functions match well the recent experimental thermodynamic functions by Meot-Ner within 1 kcal/mol. The trends of calculated hydration energies and vibrational frequencies correlate excellently with the local many-body hydrogen bond interactions in each isomer. Finally, it is proposed that the distinct spectral patterns of bonded-NH, bonded-OH, and free OH stretches can be used as fingerprints in identifying the structural isomers that contribute to the vibrational predissociation spectra.
597 - 604
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