Raman spectra from ethylene and deuterated ethylene chemisorbed on a silica-supported nickel catalyst

The Raman spectra of ethylene and deuterated ethylene chemisorbed on silica-supported nickel have been measured in the frequency range 50–3400 cm^?1. At room temperature, a Raman spectrum is observed which corresponds to ethylene chemisorbed under dehydrogenation and it is rather similar to the spectrum of chemisorbed acetylene. For a comparison therefore, the Raman spectra of acetylene and deuterated acetylene were also measured. In addition, the vibrational spectrum of chemisorbed benzene was recorded. At temperatures T ? 200 K, ethylene is found to be associatively chemisorbed without dehydrogenation.The vibrations observed are described in the approximation of a surface molecule with covalent bonding to two or three surface nickel atoms. The symmetry seems to be slightly distorted C_2v or C_s. The vibrational spectrum is discussed with respect to a metal- surface selection rule. In order to improve the reliability of the assignments for localized vibrational modes, a normal coordinate analysis and a force constant calculation have been done for chemisorbed acetylene.     

Enumerating Order Types for Small Point Sets with Applications

Order types are a means to characterize the combinatorial properties of a finite point configuration. In particular, the crossing properties of all straight-line segments spanned by a planar n-point set are reflected by its order type. We establish a complete and reliable data base for all possible order types of size n=10 or less. The data base includes a realizing point set for each order type in small integer grid representation. To our knowledge, no such project has been carried out before.We substantiate the usefulness of our data base by applying it to several problems in computational and combinatorial geometry. Problems concerning triangulations, simple polygonalizations, complete geometric graphs, and k-sets are addressed. This list of applications is not meant to be exhaustive. We believe our data base to be of value to many researchers who wish to examine their conjectures on small point configurations.     

Investigation of the metastable state of Na2[Fe(CN)5NO] · 2H2O by optical spectroscopy I. Comparison of the Raman spectra of the ground and metastable state

When excited by the 514.5 nm radiation of an argon ion laser at temperatures below 150 K crystalline sodium nitroprusside Na₂[Fe(CN)₅NO] · 2H₂O can be transformed into an extremely long-living metastable state. The Raman spectra of the crystal in the metastable state and ground state are compared in the range of 50–2350 cm^-1. In the metastable state the ?(NO)-stretching vibration is shifted by more than 100 cm^-1 to smaller frequencies depending on the orientation of the sample with respect to the crystallographic axis. This indicates the population of the antibonding π¹(NO)-orbital. In addition two new vibrations appear at 566 and 422 cm^-1. The other vibrational frequencies of the molecular ion [Fe(CN)₅NO]^2- are scarcely shifted, but relative intensities change.     

Raman and brillouin scattering in a single crystal of K2Hg(CN)4

The temperature dependence of the elastic constants of cubic K₂Hg(CN)₄ has been measured by optical Brillouin spectroscopy in the temperature range from 300-110 K. A decrease of all three elastic constants was found in agreement with the results of ultrasonic measurements. Raman measurements in the temperature range from 300-4 K revealed a splitting of the F_2g modes corresponding to a trigonal distortion of the Hg(CN)₄-tetrahedra in the low temperature phase.