Room-temperature spectra

CD] lxlO 3 M [substrate] 1 M room temperature, spectra measured after 30 min, d-doublet, s-singlet l-Phenyl-l,2-propanedione. 

Room temperature spectra were taken over the range of pressures 1-760 torr. Typical results obtained are plotted in Figure 4 along with the calculated fit of the data points to a Langmuir adsorption i sotherm. 

Room-temperature spectra of species on Ni and Pd evaporated films that were also deposited at room temperature showed spectra from a mixture of ethyne-like species, probably 7r-bonded, and alkyl species with soft rCH modes indicating agostic C-H-M interactions. 

Haaland also measured the infrared spectra of benzene adsorbed on Pt/Al203 that had been regenerated after previous benzene/cyclohexane adsorptions (247) the surface was thought to retain structured carbonaceous deposits. In this case, the broad yCH feature was centered at ca. 3030 cm 1 (with components at 3042, 3031, 3024, and 3014 cm 1) rather than 3040 cm 1 for the species on the freshly prepared catalyst, and a weaker companion band occurred at 2947 cm-1. The benzene absorption bands at wavenumbers <1500 cm 1 were little changed in position but become more prominent in room-temperature spectra in which the 2947-cm 1 feature was weakened. Spectra measured over the range 300-650 K showed that the 2947-cm 1 feature disappeared at 435 K, whereas the vCH aromatic bands retained considerable intensity at temperatures up to 560 K. 

At -61°C the H-NMR spectrum of /V-methyl-cis-octahydrocarbostyril shows signals for 8a-H in both conformers 167 and 168. On this basis Wi values were recorded from room-temperature spectra of a variety of derivatives existing as equilibria. The N-inside conformation was preferred for the JV-H compound, whereas the N-outside conformation was preferred for the N-Me compound. This is different from the situation in N-methyl-cis-decahydroquinoline and may be due to a closer approach of N-Me to the C-8 methylene in 167 than in 160 as a result of a flattened sp2-hybridized nitrogen atom.211... 

With the help of the above considerations and the single-crystal data of Table V, it is now possible to relate all the prominent features in the room-temperature spectra (Fig. 7) to surface species as follows ... 

All the room-temperature spectra have in common strong absorption bands from ethylidyne, which is therefore shown to be a particularly stable species, probably associated primarily with (111) facets on the metal particles. The room-temperature di-cr species is most consistently identifiable on large Pt particles (Figs. 7A, C, E, G, I, and J) where, because the MSSR operates, the similar-frequency parallel modes of the ethylidyne species are not expected to... 

Further progress in structural interpretations probably requires spectra on simplified single-crystal systems. Such low- and room-temperature spectra using the higher resolution of RAIRS would be particularly valuable on three of the metals, Pt, Ni or Pd, and Rh, which give different results at room temperature on the finely divided metals. 

In their original paper (2) on the structure of Fe5C(CO)l5, Dahl and co-workers assigned two bands in the infrared spectrum of hydrocarbon solutions of the cluster, at 790 and 770 cm-1, to vFeC modes. This assignment has been confirmed by a recent study of the infrared spectra of the series M5C(CO)15, (M = Fe, Ru, Os) (78). The room temperature spectra of the compounds (Table II) in the solid state are quite similar to each other, comprising three bands assigned as the a, and e modes (split in the solid state) expected for the C4 symmetry of the isostructural clusters. At low temperature the ruthenium and osmium clusters exhibit five absorptions associated with M-C stretches, whereas the iron cluster retains its room temperature spectrum. This is ascribed to the presence of two types of cluster molecule in the crystal lattices of the ruthenium and osmium clusters which are isostructural with, but not isomorphous with, the iron analog in which all the molecules are identical. 

Figure 1. X-band EPR room temperature spectra of the glass 0.63 B2O3 - 0.37 Li20 with 0.75-10 3 Fe203, annealed at the indicated temperatures during A hour.

Thus in the initial stages of the study, excitation and fluorescence spectra were measured for individual species in a cell (heated to approximately 100 C to provide sufficient vapor pressure) to determine their (near) room temperature spectra. Individual PCAH were then injected into a flame to determine the effects of flame temperatures on the spectra and to determine sensitivities. These spectra will then be used as a data base to attempt to deconvolute the complex spectra observed upon excitation of the flame itself. 

Figure 7. Room temperature absorption spectrum of CF3. The top shows a broad region while the bottom shows a small portion of the spectrum demonstrating how congested room temperature spectra can be.

Figure 6 Absorption (A) and photoluminescence (PL) room-temperature spectra of SL and DL thin film structures based on materials described in the upper part of the figure. The small green luminescence contribution of Alq3 (emission maximum at =520 nm) to the blue luminescence of TPD (emission maxima at =400 and =420 nm) for the DL film structure TPD/Alq3 excited through the TPD layer reflects the filtering action of the TPD layer for the exciting light = 355 nm. For more details, see Ref. 57.

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