Optical alignment in magic-angle NMR

A simple optical alignment system is described for adjusting the angle of the axis of rotation of an Andrews-Beams rotor in magic-angle NMR expts. A low-power ruby laser mounted between the horns of the magnet cryostat is used a light source. The beam from the laser travels vertically down the superconducting magnet bore, is deflected first by the rotor cap, then by 2 mirrors located 1 cm from the rotor and on the laser source, resp., and is projected onto a screen 5 m distant. A deviation of +-0.1 Deg from the magic angle causes the image to move by +-1 cm. Slight instabilities, such as low-frequency nutation effects, become immediately apparent upon inspection of the laser image. 13C spectra of carbonyl in glycine powder of polycryst. p-dimethoxybenzene, detd. by using the app. are shown. [on SciFinder (R)]