The rotational stateJ=1 in orientationally disordered and ordered solid hydrogen

Quantum Dynamics of H2 and D2 Confined in Hydrate Structures as a Function of Pressure and Temperature

“…The experimental value for the rotational fundamental in the gas phase (14.6 meV) is indeed very close to the predicted one, whereas in solid (phase I) hydrogen, the experimental peak associated with the rotational fundamental is broad and centered at about 14.05 meV. 39 In general, the energy shift of the rotational fundamental peak from the value of 14.6 meV can be used to monitor the degree of perturbation imposed by the molecular environment on the rotational behavior of the hydrogen molecule. As far as the molecule behaves as a free (or almost free) rotor, rotational energy levels are only marginally perturbed upon confinement with respect to those of the gas phase.…”

“…Hence, the energy difference between the ground state of p -H 2 ( J = 0) and the ground state of o -H 2 ( J = 1) is expected to be 14.74 meV; this means that the rotational fundamental is expected at 14.74 meV. The experimental value for the rotational fundamental in the gas phase (14.6 meV) is indeed very close to the predicted one, whereas in solid (phase I) hydrogen, the experimental peak associated with the rotational fundamental is broad and centered at about 14.05 meV . In general, the energy shift of the rotational fundamental peak from the value of 14.6 meV can be used to monitor the degree of perturbation imposed by the molecular environment on the rotational behavior of the hydrogen molecule.…”

Manipulation of the crystalline phase diagram of hydrogen through nanoscale confinement effects in porous carbons

“…This can be semi-quantitatively observed in the changes to the rotational energy spectrum. In the micropores of TE7, the rotational energy of confined ortho-H 2 was observed at 13.3 meV and 8 meV as compared to 13.7 meV for bulk FCC ortho-H 2 28,30 indicating the confined ortho-H 2 is in a lower rotational energy state than the bulk. Likewise, the calculated potential barriers to rotation in the confined phase are much higher than the EQQ coupling binding energy observed and calculated in the bulk phase.…”

“…This binding energy can be correlated to a drop in the rotational energy across the bulk HCP-FCC transition for various concentrations of ortho-H 2 . 28,30 As the concentration of ortho-H 2 increases in the solid, the observed binding energy in the solid also increases. Consequently, increasing EQQ coupling in the solid raises the HCP-FCC transition temperature in tandem.…”

“…Likewise, the calculated potential barriers to rotation in the confined phase are much higher than the EQQ coupling binding energy observed and calculated in the bulk phase. 28,30,68,75 With this understanding of how confinement can affect the phase behaviour of H 2 , the thermal stability of the confined phase could theoretically be increased further. If other materials that exhibit preferential adsorption, high enthalpies of adsorption and significant perturbations to the rotational degrees of freedom of H 2 , can be engineered to have subnanometre pores similar to those shown in activated carbons, the overlap of anisotropic potential will be much greater and enhance the confinement effects, increasing the proportion and thermal stability of confined FCC ortho-H 2 higher than observed here.…”