Naoki Osaka

Infrared reflection absorption spectroscopic study on adsorption structures of acrylic acids on evaporated silver films under ultra-high vacuum conditions

Abstract Infrared reflection absorption spectra were measured under ultra-high vacuum conditions for acrylic acid adsorbed on evaporated silver films. The spectral features especially associated with out-of-plane vibrations including an OH out-of-plane bending (γ(OH)) vibration were found to be very useful to identify the adsorption structures. The features at 90 K clearly indicate that, upon increasing exposure levels, the adsorbates form type-A, -B and -C states successively. The type-A state coordinates directly to the surface through the CO group; upon forming a few monolayers the adsorbate occurs mainly in the type-B state and on a further increase of monolayers the adsorbate is converted to the type C. Both type-B and -C states form a hydrogen-bonded cyclic dimer with the molecular plane parallel to the surface. The dimeric structure of type B is perturbed by an interaction with the surface, as judged from appreciable spectral changes of the out-of-plane vibrations compared to those of the type C. The type C forms a state similar to acrylic acid in a crystalline state. The γ(OH) band of the type C, however, is observed at 916 cm−1, which is higher than that of the crystalline state by 21 cm−1, indicating that stacking of the dimeric units in the type-C adsorbate exerts a stronger restraining force on the OH group than stacking in the crystalline state.

Infrared reflection–absorption spectroscopic study on the adsorption structures of acrylonitrile on Ag(111) and Ag(110) surfaces

Infrared reflection-absorption spectra in CN stretching, CH 2 out-of-plane wagging and CH 2 twisting vibration regions were measured for acrylonitrile (CH 2 =CHCN) exposed to Ag(111) and Ag(110) in increasing amounts at 77 K. The adsorbate on Ag(111) takes on a series of discrete adsorption states; i.e., an isolated state, associated states, and ordered and amorphous multilayer states. The adsorbate on Ag(110) at lower exposures is in a state with the CN group weakly coordinated to a silver atom (or silver atoms). The adsorbate on Ag(110) takes the associated state and the amorphous multilayer at larger exposures. On raising the temperature to 96 K, the amorphous states on both Ag(111) and Ag(110) are converted to the ordered multilayer. The desorption temperature of the ordered multilayer is below 99 K for Ag(110), while the temperature is above 107 K for Ag(111); the result indicates the effect of the surface morphology on the stability of the ordered state.