is partially eliminated by imposing this PNC, which allows us to identify the marginal photon-nuclear probability density as |χ(q, R,t)| 2 = dr|Ψ(r, q, R,t)| 2 . As a result of the PNC, the two wavefunctions are uniquely defined up to a phase factor e ±iθ (q,R,t) , with θ (q, R,t) being a real function.