Rotational state modification and fast ortho-para conversion of H2 trapped within the highly anisotropic potential of Pd(210)

Rotational-Energy Transfer in H2 Ortho–Para Conversion on a Metal Surface: Interplay between Electron and Phonon Systems

“…As shown in a previous theoretical study, the adsorption potential of H 2 molecularly chemisorbed on top of step-edge Pd of Pd(210) is highly anisotropic where the potential for the orientation with the H 2 molecular axis in the parallel orientation with respect to the surface has a deeper well relative to the perpendicular orientation . This potential induces lifting of the rotational-state degeneracy of H 2 . − While in the gas phase the J = 1 state is triply degenerate, the lowest o- H 2 in the adsorption state, labeled as J ′ = 1, is doubly degenerate ( m = ± 1) as shown in Figure , where the lowest J ( J ′) = 0 and second-lowest J ( J ′) = 1 rotational states correspond to the para and ortho states in the gas phase (in the adsorption state). In order to probe surface-adsorbed H 2 in J ′ = 0 and J ′ = 1 a combination technique of a pulsed molecular beam, photostimulated desorption (PSD), and resonance-enhanced multiphoton ionization (REMPI) is used .…”

“…This corresponds to the rotational energy difference between both species ( E rot ) in the adsorption state, which is smaller than the value of 14.7 meV in the gas phase. This is qualitatively consistent with previous reports showing that the rotational-energy difference between o- H 2 and p- H 2 gets smaller than that of the gas phase as shown in Figure . , …”

“…This is qualitatively consistent with previous reports showing that the rotational-energy difference between o-H 2 and p-H 2 gets smaller than that of the gas phase as shown in Figure 1. 14,15 In the o−p conversion accompanied by a rotational-state transition, the associated rotational energy is transferred to electron and/or phonon systems. We discuss here the roles of electrons and phonons in the rotational-energy transfer for the o−p conversion.…”

Dynamical Quantum Filtering via Enhanced Scattering of para-H2 on the Orientationally Anisotropic Potential of SrTiO3(001)

“…) results in adsorbed H 2 with (hindered) rotational states (J, m) different from that of gas phase H 2 . These strongly hindered adsorption states lead to (J, m)-dependent thermal desorption energies [24][25][26][27][28][29][30] , suggesting the possibility of separating para-H 2 [p-H 2 (J = 0, m = 0)] and ortho-H 2 [o-H 2 (J = 1, m = ±1)] through an adsorption-desorption process. This could find significant applications not only in H 2 storage and transport applications, but also in realizing materials with pre-determined characteristic properties.…”

“…In the following, we will show that on STO(001), under the influence of the orientationally anisotropic potential, on top of the surface lateral corrugation, p-H 2 scatter strongly at specific angles from the TiO 2 -terminated and SrO-terminated STO(001). This dynamical filtering/scattering selectivity allows for more economical (less heat consumption) and more efficient means to rotationally separate o-H 2 and p-H 2 , than the usual adsorption-desorption process [1][2][3][4][5][24][25][26][27][28][29][30] . Figure 1 shows a H 2 interacting with STO(001).…”