  The Transactional Interpretation of quantum mechanics exploits the intrinsic
time-symmetry of wave mechanics to interpret the $\psi$ and $\psi$* wave
functions present in all wave mechanics calculations as representing retarded
and advanced waves moving in opposite time directions that form a quantum
"handshake" or transaction. This handshake is a 4D standing-wave that builds up
across space-time to transfer the conserved quantities of energy, momentum, and
angular momentum in an interaction. Here we derive a two-atom quantum formalism
describing a transaction. We show that the bi-directional electromagnetic
coupling between atoms can be factored into a matched pair of vector potential
Green's functions: one retarded and one advanced, and that this combination
uniquely enforces the conservation of energy in a transaction. Thus factored,
the single-electron wave functions of electromagnetically-coupled atoms can be
analyzed using Schr\"odinger's original wave mechanics. The technique
generalizes to any number of electromagnetically coupled single-electron
states---no higher-dimensional space is needed. Using this technique, we show a
worked example of the transfer of energy from a hydrogen atom in an excited
state to a nearby hydrogen atom in its ground state. It is seen that the
initial exchange creates a dynamically unstable situation that avalanches to
the completed transaction, demonstrating that wave function collapse,
considered mysterious in the literature, can be implemented with solutions of
Schr\"odinger's original wave mechanics, coupled by this unique combination of
retarded/advanced vector potentials, without the introduction of any additional
mechanism or formalism. We also analyse a simplified version of the
photon-splitting and Freedman-Clauser three-electron experiments and show that
their results can be predicted by this formalism.
