Specifically, INS can examine rotational transitions of an H2 molecule bound to a metal, and thus has been used to probe the barrier of rotation of an H2 molecule bound to a metal or the elongation of the H-H bond due to π-backbonding using the rotational constant B. We note that INS measurements for Cu I Cd-MFU-4l are also hindered by the large neutron absorption cross-section of naturally abundant isotopes of Cd. The background subtracted INS spectrum for Cu I Mn-MFU-4l dosed with 0.75 equivalents of para-H2 are plotted in Figure . The spectrum shows four peaks in the low energy transfer region, occurring at energy transfer values of 5.278(6), 5.714(3), 6.098(3), and 6.642(8) meV. Given the relative intensities, we tentatively attribute these peaks as two sets of splitting peaks with J = 0 to J = 1 rotational excitations for para-H2 in slightly different rotational potential environments. Additional features are observed between 30 and 45 meV (Figure ), which can be assigned as combination bands and overtones from H2 on the same binding sites as the low energy transfer peaks, as observed in similar studies. Figure . INS spectra for Cu I Mn-MFU-4l (green) and Cu I Zn-MFU-4l (blue) dosed with para-H2 from 2 to 15 meV. A spectrum shown here is difference between the spectrum of an activated framework and that after para-H2 dosing.