The rate determining step for the neutral pH dimerization process has a zero-point corrected activation energy of 70.7 kJ/mol for the pure water system and 59.8 kJ/mol for the salt-present system (eqns A1 and B2 in table 2), which strongly suggests that the zwitterion pathway is a good candidate for the dimerization mechanism in neutral pH. According to experimental studies , the activation energy for this reaction should be between 12.6 kJ/mol and 71 kJ/mol and therefore, the results of this study are in excellent agreement with experiment. In comparison, the mechanism previously reported by has an activation energy of 127 kJ/mol for the rate-determining step, while that of has an activation energy of 133 kJ/mol.