Laboratory microwave data

The purpose of this report is to demonstrate the ease with which highly accurate equilibrium structures can be determined by combining laboratory microwave data with the results of ab initio calculations. In this procedure, the effects of vibration-rotation interaction are calculated and removed from the observed rotational constants, Aq, Bq and Cq. The resulting values correspond to approximate rigid-rotor constants and and are thus inversely... 

Work is in progress in several laboratories to obtain more precise experimental results, largely by taking into account microwave data. Any revisions of bond angles will also necessitate changes in the calculated lengths of approach (iO... 

The equilibrium structural parameters re(HN) = 1.03359(43) A and re(NN) = 1.092766(92) A were obtained from the rotational constants [20]. The substitution structural parameters s(HN) = 1.031426(56) A and rs(NN) = 1.095415(6) A, obtained from microwave data on several isotopomers [33], apparently supersede earlier r values which were determined in the same laboratory [17, 31, 32]. The geometric structure was also calculated from microwave data [32] using a mass-dependent scaling of the moments of inertia [34]. 

The Jet Propulsion Laboratory (JPL) research team have successfully flown the Microwave Limb Sounder (MLS) aboard the Upper Atmospheric Research Satellite (UARS), which has been measuring stratospheric profiles of CIO, O3, H20 and HN03 since 1992 (Waters et al., 1993) (Table 1). In total some 140 publications have been published on the basis of MLS data. The Microwave Atmospheric Sounder (MAS) flew three times aboard the Shuttle also measuring CIO, 03 and H20 and has also provided a unique set of observations (Hartmann et al., 1996). 

In 1988, Riis et al. [52] observed a direction-dependent anisotropy of light in the direction of the apex of the 2.7 K microwave background radiation in the universe. These data are consistent with nonzero photon mass. The upper bound on photon mass was estimated as mT 10-65g. A compilation of laboratory data [53] established that the photon mass should not exceed 10-24 eV or even 10 26 eV. 

One laboratory reported a (71 + 6)% recovery which was lower than for other species and a possible over-estimation was suspected the set of data was consequently withdrawn. The use of an ultrasonic stage in the extraction in the GC-MIP method (giving a 70% recovery) could be responsible for the apparent over-estimation of the results another laboratory used a microwave method and did not observe such over-estimation. 

Also using K-10 clay as a support, an experiment illustrating the Fries rearrangement has been reported for use in an undergraduate laboratory, in which the P-napthylacetate and the steroid estrone are used as substrates (Scheme 6.7). Drawbacks, however, are the use of a domestic microwave, open beakers as reaction vessels, and the vague experimental details provided. The protocol calls for heating the reaction at power level 9 for 10 min. In the absence of temperature data, it would be hard to reproduce the experiment without reoptimization. 

To show an application of the method of linear least squares to data collected in a laboratory, a procedure has been developed in which a beaker containing water was heated in a domestic microwave oven, and the water temperature measured as a function of time and power. Students obtained a regression line for each power level screened and determined the intercept and slope of the line. They then compared and contrasted the values obtained for initial temperature and power input using the linear regression with those set experimentally, outlining sources of error. 

Overall, faculty have seen a 25% increase in productivity in the laboratories. The incorporation of microwave heating has expanded the range of chemical concepts that can be introduced through hands-on learning. There is less crowding at the end of the laboratory time around the NMR and IR spectrometers and melting point apparatus, since the time for collecting data has nearly doubled. 

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