X-ray precession

The EPR/ENDOR measurements described here have been performed on single crystals which are accurately oriented with an x-ray precession camera, x-ray irradiated, and observed at ca. 10 K. The schematic diagram of the X-band EPR apparatus is shown in Figure 18-1 [12], This cavity is a modification of one previously described by Weil et al. [13], The EPR cavity is essentially a cast epoxy, wire wound TE011 cylindrical cavity with external 100 kHz modulation coils. The Cryo-Tip portion of the cavity can be raised 6 cm for x-irradiation and subsequently lowered into the microwave cavity for EPR measurements [14], In the microwave cavity the lowest temperature of the sample is approximately 6 K. However in the irradiation position the lowest temperature is about 10 K because the sample is not as effectively heat-shielded from the room temperature vacuum shroud. 

The Raman spectrum of a single crystal sample, which was characterized by x-ray precession data, as the form stable at room temperature, showed no significant differences from the spectra from microcrystalline samples. The bands, with relative intensities in parentheses, are 719(25) 667(102) 620(100) 574(21) 523(sh ) 498(66) 393(12) 373(10) 298 cm- (17). The spectrum is illustrated in Fig. 3. 

Figure 4.51. Myoglobin Crystal and X-Ray. (A) Crystal of myoglobin. (B) X-ray precession photograph of a myoglobin crystal. [(A) Mel Pollinger/Fran Heyl Associates.]... 

The control of the tilt and azimuthal angles of (100) faces is important to improve the quality of HOD films. In Ref. [264], the tilt (x) and azimuthal 4>) misorientation angles of the (100) faces were measured by both the X-ray precession method and the X-ray rocking curve measurements for HOD films with thicknesses of 1, 4, 20, and 100 pm, which were made by the three-step process (see Figure 5.3). The results are shown in Figure 11.8. 

X-Rav and Compositional Analyses. Single crystal x-ray precession photographs of YBC crystals from the Pt and Au crucible runs confirmed their perovskite-related structure. Crystal composition was determined by electron microprobe analysis. The Y/Ba/Cu ratios were 1/2/3 in each crystal within the accuracy of the microprobe measurements. However, the crystals grown in Au crucibles contained approximately 0.7 mole% Au. 

Of the many types of X-ray cameras, only two are still in even occasional use in protein crystallography — the Buerger or precession camera and the rotation/oscillation camera. The precession camera is used primarily in... 

The precession camera (Fig. 4.23), although the more complicated in its motion, produces the simplest diffraction pattern. X rays enter through the black tube at left to strike the crystal, mounted in a goniometer head. Beyond the crystal are an annular-screen holder (smaller black square) and a film holder (larger black square). The remaining machinery moves crystal, screen, and film in a precessing motion about the X-ray beam. 

Some Properties of Xe(OSOtF)2.— Die Raman spectrum is compared with those of FXeOSOtF and StOoFt in Table III. Single crystals of Xe(OS02F)t were obtained by slow evaporation of a HF solution and fragmentary precession photograph data, from such a crystal, provided for the indexing of the X-ray powder data given in Table IV. The unit cell is monoclinic with a = 7.94, b = 13.7, c = 6.84 A, 0 = 96 . A small sample of Xe(OSOtF)2 under a dynamic vacuum at 20 slowly decomposed but none of the compound collected in the limbs of a U tube, cooled at —75°, provided to trap it. 

The crystal used for data coUection was transferred to an Enraf-Nonius CAD-4 diffractometer. Automatic peak search and indexing procedures yielded the same monoclinic cell as derived from the X-ray powder diffraction data and precession photographs. Testing showed that the cell was indeed primitive and that there was no superlattice present. Table 5 gives the crystal data and X-ray experimental parameters, and Table 6, the interatomic distances and angles. Positional and thermal parameters are given in Table S3 (Supporting Information)... 

Colorless crystals were formed upon sublimation of the micro-crystalline solid at 40-50 C in 0.7-mm-diameter quartz X-ray capillaries. These had been sealed under an atmosphere of nitrogen. Precession photographs indicated a primidve orthorhombic cell, space group Pnma or Pna2i. 

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