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A model study on the mechanism and kinetics for the dissociation of water anion
Author(s) -
Huyen Trinh Le,
Duong Long Van,
Nguyen Minh Tho,
Lin Ming Chang
Publication year - 2019
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/kin.21281
Subject(s) - chemistry , aqueous solution , dissociation (chemistry) , reaction rate constant , molecule , polarizable continuum model , ion , computational chemistry , hydrogen bond , density functional theory , transition state , crystallography , kinetics , solvation , catalysis , organic chemistry , physics , quantum mechanics
Quantum chemical computations using both density functional theory (B3LYP functional) and wavefunction (MP2 and CCSD(T)) methods, with the 6‐311++G(3df,2p) and aug‐cc‐pV n Z ( n = D,T,Q) basis sets, in conjunction with a polarizable continuum model (PCM) method for treating structures in solution, were carried out to look again at a series of small negatively charged water species [(H 2 O) n ] •– . For each size n of [(H 2 O) n ] •– in aqueous solution with n = 2, 3, and 4, two distinct structural motifs can be identified: a classical water radical anion formed by hydrogen bonds and a molecular pincer in which the excess electron is directly interacting with H atoms. In aqueous solution, both motifs have comparable energy content and likely coexist and compete for the ground state. Some water anion isomers can dissociate when interaction with a water molecule, [(H 2 O) n ] •– + H 2 O → H • (H 2 O) m + OH – (H 2 O) n – m , through successive hydrogen transfers with moderate energy barriers. This reaction can also be regarded as a water‐splitting process in which the H transfers involved take place mainly within a water trimer, whereas other water molecules tend to stabilize transition structures through microsolvation rather than direct participation. Calculated absolute rate constants for the reversed reaction H • (H 2 O) 2 + OH – (H 2 O) 2 → [(H 2 O) 4 ] • ־ + H 2 O with both H and D isotopes agree well with the experimentally evaluated counterpart and lend a kinetic support for the involvement of a tetramer unit.