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In the last few years, infrared reflection-absorption spectroscopy (IRRAS) has become a standard technique to study vibrational excitations of molecules. These investigations are strongly motivated by potential applications in monitoring chemical processes. For a better understanding of the adsorption mechanism of molecules on dielectrics, the polarization-dependence of an interaction of infrared light with adsorbates on dielectric surfaces is commonly used. Thus, the peak positions in absorption spectra could be different for s- and p-polarized light. This shift between the peak positions depends on both the molecule itself and the dielectric substrate. While the origin of this shift is well understood for infinite two-dimensional adsorbate layers, finite-size samples, which consist of 2D islands of a small number of molecules, have never been considered. Here, we present a study on polarization-dependent finite-size effects in the optical response of such islands on dielectric substrates. The study uses a multi-scale modeling approach that connects quantum chemistry calculations with Maxwell scattering simulations. We distinguish the optical response of a single molecule, a finite number of molecules, and a two-dimensional adsorbate layer. We analyze CO and CO2 molecules deposited on CeO2 and Al2O3 substrates. The evolution of the shift between the polarization-dependent absorbance peaks is first studied for a single molecule, which does not exhibit any shifting at all, and for finite molecular islands, where it increases with increasing island size, as well as for an infinite two-dimensional adsorbate layer. In the latter case, the agreement between the obtained results and the experimental IRRAS data and more traditional three/four-layer model theoretical studies supports the predictive power of the multi-scale approach. [ABSTRACT FROM AUTHOR]

The microporous and activated zeolitic imidazolate framework (Zn(MeIM)2; MeIM = imidazolate-2-methyl; ZIF-8) was loaded with the MOCVD precursor diethyl zinc [Zn(C2H5)2]. Exposure of ZIF-8 to the vapour of the volatile organometallic molecule resulted in the formation of the inclusion compound [Zn(C2H5)2]0.38@ZIF-8 revealing two precursor molecules per cavity. In a second step the obtained material was treated with oxygen (5 vol% in argon) at various temperatures (oxidative annealing) to achieve the composite material ZnO0.35@ZIF-8. The new material was characterized with powder XRD, FT-IR, UV-vis, solid state NMR, elemental analysis, N2sorption measurements, and transmission electron microscopy. The data give evidence for the presence of nano-sized ZnO particles stabilized by ZIF-8 showing a blue-shift of the UV-vis absorption caused by quantum size effect (QSE). The surface structure and reactivity of embedded ZnO nanoparticles were characterized viacarbon dioxide adsorption at different temperatures monitored by ultra-high vacuum FTIR techniques. It was found that the surface of ZnO nanoparticles is dominated by polar O–ZnO and Zn–ZnO facets as well as by defect sites, which all exhibit high reactivity towards CO2activation forming various adsorbed carbonate and chemisorbed CO2δ−species. [ABSTRACT FROM AUTHOR]

The interaction of water with ZnO nanoparticles has been studied by means of diffuse reflectance infrared spectroscopy (DRIFTS) and ultra-high vacuum FTIR spectroscopy (UHV-FTIRS). Exposing clean ZnO powder to water at 323 K leads to both molecular and dissociative adsorption of H2O forming a number of hydroxyl species. All the OH bands are clearly identified by the adsorption of D2O showing the expected isotopic shifts. According to the vibrational and thermal stability data obtained from single crystal surfaces, the OH species observed on ZnO nanoparticles are identified as follows: (1) OH group (3620 cm−1) on the polar O–ZnO(0001) surface formed viadissociation of water on oxygen vacancy sites; (2) partial dissociation of water on the mixed-terminated ZnO(1010) surface yielding coexistent H2O (∼3150 and 3687 cm−1) and OH species (3672 cm−1), where the molecularly adsorbed H2O is further identified by the characteristic scissoring mode at 1617 cm−1; (3) isolated OH species (3639 and 3656 cm−1) formed on the mixed-terminated ZnO(1010) surface; (4) interaction of water with defects forming hydroxyl (or O–HO) species (3564 and 3448 cm−1). [ABSTRACT FROM AUTHOR]

Nanoscale titania particles were synthesized inside the porous coordination polymer [Zn4O(bdc)3] (bdc = 1,4-benzene-dicarboxylate, MOF-5) by adsorption of titanium isopropoxide from the gas-phase and subsequent dry oxidation and annealing. [ABSTRACT FROM AUTHOR]