Microwave spectra comparison with

Breslow etal.133 investigated the microwave spectrum of cyclopropenone and determined data for bond lengths, bond angles, dipole moment (4.39 D from the molecular Stark effect), and magnetic susceptibility anisotropy (Ax) as seen in Table 5 in comparison with cyclopropene5 3 ... 

Additional spectroscopic data were available, which have, however, less frequently been used for comparison with theoretical calculations. These comprise the UV spectrum. Ref. 20, and the microwave spectrum of 4 (a) R. D. Brown, P. D. Godfrey, and M. J. Rodler, J. Am. Chem. Soc. 1986, 108, 1296. The dipolar C NMR spectrum of 1,2-[ C]2-4 in an argon matrix was measured and analyzed in order to determine the C=C distance., cf. Ref. 24. A detailed comparison of measured and calculated chemical shifts is given in (b) H. Jiao, P. v. R. Schleyer, B. R. Beno, K. N. Houk, and R. Warmuth, Angew. Chem. 1997, 109, 2929 Angew. Chem. Int. Ed. Engl. 1997, 36, 2761. 

Figure 6 These two structures of the Xe-(H20)2 complex correspond to the two minima found in ah initio calcnlations on the MP2 level for this system. An interpretation of the nnclear quadrupole coupling constants and comparison with the corresponding constant in Xe-H20 reveal that the structure in (a) is consistent with the data from the microwave spectrum...

It has been possible to use the statistics from the least squares fit of the microwave spectrum through propagation of errors formulas (including the correlation of errors between the determined rotational and distortion constants) to calculate standard deviations for the force constants calculated from the distortion constants. These standard deviations, which represent measurement errors, can be compared with the lack of internal consistency between force constants calculated from different distortion constants. This comparison gives the relative magnitude of measurement vs. model errors. 

CHjCO Ketene is the prototype for this series of compounds. It is readily prepared by the pyrolysis of acetone, acetic anhydride and other simple precursors. The monomer has limited stability due to the ease with which it dimerizes. The haloketenes and other small, substituted ketenes are reactive enough to be considered transient molecules. Ketene has been studied spectroscopically since the first report of its liquid phase Raman spectrum in 1936 by Kopper The main interest comes from the comparison with formaldehyde. Although the molecular structure of ketene is only marginaUy larger, with one extra atom, the microwave, infrared and UV-visible spectra are much more complex than those of CH O. 

Comparison of the flash-induced T-S spectrum [9] with the ADMR-detected T-S spectrum at 509 or 982 MHz, shows that both spectra have an identical shape around the Qy maximum, including the shoulder at 785 nm. The positive contribution between 805 and 815 nm in the ADMR-detected T-S spectrum is not seen in the flash-induced T-S spectrum. The ADMR-detected T-S spectrum shows more structure than the flash-induced T-S spectrum, which can easily be explained by the fact that the selectivity with resonant microwaves used by ADMR allows better discrimination than flash spectroscopy when several triplets are present with triplet lifetimes in the same order of magnitude. Smit et al. [5] and Kleinherenbrink et al. [9] attributed the flash-induced T-S spectrum to the triplet state of the primary donor, formed by radical recombination. As the ADMR signal increases when the sample is frozen under illumination our measurements confirm this conclusion. The appearance of the acceptor signal at 670 nm, which is only seen in the spectra recorded at 473, 509 and 982 MHz, is further evidence that these transitions belong to the reaction center triplet. 

Figure 6 shows a comparison of typical experimental data for the symmetric top molecule CH3CI with the theoretical spectrum predicted by Eqs. (37) and (51). It appears that the model provides a reasonable description of both the microwave and far-infrared spectra for this species with a fair description of the temperature dependence. 

ArH" Combined analysis of microwave and IR data in [84Joh]. The A parameters contain only the adiabatic contribution, compare [87Lau]. Pure rotational spectrum [88Bro] confirms the rotational constants in [84Joh]. A combined analysis was performed by [88Gru] to derive directly the potential function in an expansion with Morse potentials, the conventional Dunham approach seems to be not appropriate. Frequencies of pure rotational transitions reported in [87Liu], only theoretical comparison made. 

Figure 16. Observation of Fe-ENDOR for the two [2Fe2S] clusters in quinoline oxidore-ductase (Qor). The top part of the left panel shows the field-swept ESE spectrum with the arrows indicating the principal components of the g-tensors of both clusters (FeSII and FeSI). The sticks mark the field positions for which the ENDOR spectra of Fe-substituted Qor (solid traces) and Fe-Qor (dotted traces) are compared in the bottom part of the left panel. In the high-fi equency part the resonances of the Fe ions of both centers are visible. The resonances of Fe appear only weakly in a narrow field range (ca. 359 mT) at low rf frequencies. The right panel shows the experimental line positions of the Fe resonances (filled squares) and the simulation of the outer lines of the Fe interaction arising from FeSII (open circles, dotted line) and FeSI (open squares, dotted line) for comparison. The data-points were taken from CW difference spectra ( Fe vs. Fe) note that the microwave frequency for this panel is different from that in the left part, yielding shifted magnetic field values for related working points. The swept radiofrequency is denoted Urf...

The rotational lines of ammonia (NH3) below 250 cm can easily be identified in the Jovian spectrum, but they are less prominent on Saturn, and completely absent on Uranus and Neptune. A comparison of the vapor pressure curve of NH3 with the ambient temperatures on these planets indicates that the atmospheres of Uranus and Neptune are just too cold to contain much NH3 in gaseous form at the pressure levels pertinent to these measurements, that is, at pressures up to about one bar. If NH3 were pushed up with a pocket of gas from lower levels, it would first supercool and, eventually, form small ice crystals. Earth-based measurements of the microwave... 

---