Vibrational spectroscopy of adsorbed hydrogenous species studied by inelastic incoherent neutron scattering

Abstract

Inelastic incoherent neutron scattering (INS) spectra of hydrogen strongly chemisorbed at coverages of greater than one monolayer on Pd black (Drijfhout, Amsterdam) were obtained (77K) without interference from adsorbed or type-C adsorbed hydrogen. The spectra were assigned by comparison with the vibrational spectra of transition-metal hydridocarbonyl compounds and indicated the occupation by H of two-fold bridging and terminal sites, the relative population of the terminal sites increasing at higher hydrogen coverage. INS spectra (ca 20 to 850 cm(^-1); 10, 16 and 77K) of c-C(_3)H(_6) adsorbed in Co(_4)Na(_4)Al(_12)Si(_12)O(_48), and of c-C(_3)H(_6) and c-C(_3)D(_6) in Mn(_3.5)Na(_5)Al(_12)Si(_12)O(_48) zeolite were consistent with C(_3v) symmetry of the M(II)-cyclopropane sorption complexes (M=Co or Mn). INS spectra (320 to 2230 cm(^-1); 77K) of Kadox 25 ZnO and H(_2) adsorbed on ZnO were obtained. The ѵ(_s) and ѵ(_δ) modes of type I Zn-H surface species were observed at 829 and 1708 cm(^-1). Recent assignments in the literature of the ѵ(_δ) mode of type I O-H species and the ѵ(_as) mode of type II Zn-H-Zn species to weak IR bands at 850 and 1475 cm(^-1) respectively were not corroborated by the INS results. The INS spectrum of ZnO contained an intense feature at 1346 cm(^-1) which was unchanged on adsorption, and assigned to bulk impurities. Raman and IR data of ZnO were also discussed. INS spectra (ca 20 to 850 cm(^-1); 10 and 77K) of C(_2)H(_2) and C(_2)D(_2) adsorbed in partially Ni(^++) ion-exchanged zeolite-Y indicated that the admolecules were non-linear (C(_2v) symmetry) and laterally bonded to the surface.. Bands centred at 774, 684, 546 and 75 cm(^-1) in the INS spectra (ca 20 to 850 cm(^-1); 10 and 77K) of H(_2)O adsorbed in Ca(_6)Al(_12)Si(_12)O(_48) zeolite at coverages of one H(_2)O molecule per Ca"*"*" ion or less were assigned to the wagging, twisting and rocking modes and to the doubly degenerate hindered translations parallel to the surface, respectively of H2O adsorbed at Ca"*"^ sites.INS spectra (lOK) of adsorbed by Zn^ ^Na^ 0^12 5^^11 5^48 ^^^^^^ showed bands at 72 and 155 cm""'", assigned to the tunnelling transitions E^^Eg and E^-^B respectively between the sublevels of the ground torsicxial state of a rigid H2 rotor, coifined to a plane parallel to the adsorbed surface, in a six-fold potential well of barrier height 29±3 kJ mol""'".