Functional RNAs fold into compact, well-defined tertiary structures despite strong electrostatic repulsion both within and between helices. To achieve these compact structures, many RNAs employ structural divalent cations, typically Mg2+. The simplest tertiary contact in nucleic acids is two helices, joined by some non-helical contact. To explore the fundamental characteristics of tertiary contact formation in nucleic acids we studied a system of two DNA helices tethered via a short PEG linker by both computational and experimental methods. Computationally, we predict the electrostatic repulsion between these helices as a function of Mg2+ and Na+ concentration. Experimentally, we linked the distal termini of these helices via a disulfide linker. Using small-angle x-ray scattering, we measured the fraction of intact disulfide bonds as a function of reducing strength of the buffer at a range of Mg2+ and Na+ concentration. Using these data we can extrapolate the magnitude of the strain on the disulfide bond, and thus the repulsion between the helices. Previous results show that the conformational ensemble is narrowly distributed around an extended, co-linear conformation at low salt and becomes more relaxed at high salt, but is unable to isolate a conformation in which the helices are stacked. Furthermore, previous results also suggest that specific interactions between Mg2+ and the phosphate backbone strongly are more important than simple ionic strength in determining the magnitude of the repulsive potential between the helices. In this project, we hope to experimentally demonstrate the energy of helix stacking and the different role of ionic strength and ionic specific interactions.