  We study NaCl ion-pair dissociation in a dilute aqueous solution using
computer simulations both for the full system with long range Coulomb
interactions and for a well chosen reference system with short range
intermolecular interactions. Analyzing results using concepts from Local
Molecular Field (LMF) theory and the recently proposed AI-based analysis tool
"State predictive information bottleneck" (SPIB) we show that the system with
short range interactions can accurately reproduce the transition rate for the
dissociation process, the dynamics for moving between the underlying metastable
states, and the transition state ensemble. Contributions from long range
interactions can be largely neglected for these processes because long range
forces from the direct interionic Coulomb interactions are almost completely
canceled ($>90\%$) by those from solvent interactions over the length scale
where the transition takes place. Thus for this important monovalent ion-pair
system, short range forces alone are able to capture detailed consequences of
the collective solvent motion, allowing the use of physically suggestive and
computationally efficient short range models for the disassociation event. We
believe that the framework here should be applicable to disentangling
mechanisms for more complex processes such as multivalent ion disassociation,
where previous work has suggested that long range contributions may be more
important.
