We develop a procedure to determine excited states potentials from photofragmentation data using adiabatic energy curves. The adiabatic curves, obtained from empirically derived diabatic channel potentials, are inverted to yield a polyatomic potential energy surface which is expressed as a piecewise collection of diatomic cuts. The procedure is applied to obtaining a two-dimensional potential of the FNO molecule in the S-1 excited state. The potential is more successful than available ab initio surfaces in reproducing the observed asymmetric (Fano) line shapes of the FNO S-1<--S-0 state-specific photofragment yield spectra.