Oscillation camera data processing. 3. General diffraction spot size, shape and energy profile: formalism for polychromatic diffraction experiments with monochromatized synchrotron X-radiation from a singly bent triangular monochromator

The size and shape of diffraction spots produced by monochromated synchrotron X-radiation from a singly bent triangular monochromator are derived following a simpler more comparative treatment given in earlier work on reflecting range and prediction of partiality for oscillation camera data [Greenhough & Helliwell (1982). J. Appl. Cryst. 15, 493–508]. In that treatment the possibility of a polychromatic experiment {[see Arndt Nucl. Instrum. Methods (1978), 152, 307–311] for an earlier suggestion} was identified and here the energy profile within each diffraction spot is derived along with the spectral resolution ∂E/E at any point in the profile due to experimental conditions and sample characteristics. A firm theoretical basis is established so that experimental problems and procedures can be discussed with a view to optimizing the method in the light of the presentation of the first reported polychromatic experiment [Arndt, Greenhough, Helliwell, Howard, Rule & Thompson (1982). Nature (London), 298, 835–838].