The Hamiltonian was then projected into a finite expansion basis taking solutions of the harmonic oscillator model as the basis functions. For the calculations we report, 20 basis states were considered, ensuring convergence of the anharmonic correction to roughly 10 -4 cm -1 . By diagonalization of the Hamiltonian, we can find the eigenstates within the discrete space considered. The energy difference between the ground and the first excited vibrational state was then used as the anharmonically corrected vibrational frequency of H2 bound to the framework.