Seya-Namioka

Photoionization, as already pointed out, is characterized by a step function for ionization probabiUty versus energy. The change in mode of ionization is thus much more easily detectable than for electron impact which produces only changes of slope. The combination of photon impact ion sources with mass analysis has been a major advance in technique since it has allowed the direct study of formation and breakdown of excited ions. The first account of such an experiment was given by Hurzeler, Inghram and Morrison (1958) who employed the especially convenient Seya-Namioka type of monochromator, which had then just been described, in conjunction with a conventional magnetic sector mass... 

Fig. 19. Important optical mountings for optical spectrometers with a plane (A Ebert, B Czerny-Turner) and a concave (C Seya-Namioka, D Paschen-Runge) grating, m Mirror, se entrance slit, sa exit slit, gp plane grating, gc concave grating.

The vacuum ultraviolet photolysis source was a krypton resonance lamp, constructed with some modifications according to the design of workers at the National Bureau of Standards (22, 29). This lamp, fitted with lithium fluoride windows, was sealed directly to the reaction vessel whose volume was ca. 50 cc. The spectral emission of the lamp was examined with a scanning monochromator of the Seya-Namioka type. Some 75% of the emission in the region 1000-1600 A. was found to consist of the 1236-A. line. All photolysis experiments were carried out with a sample pressure of 40 mm. Hg. In addition to the 1236-A. line,... 

The spectrometers used are adapted either for sequential or simultaneous multi-element measurements. Commonly used grating spectrometers in plasma AES include (i) spectrometers with the Paschen-Runge mount, (ii) echelle spectrometers, (iii) spectrometers with Ebert and Czerny-Turner mounts, (iv) spectrometers with Seya-Namioka mounts, and (v) double monochromators. Also Fourier transform spectrometers may be used in plasma AES. 

The grating is rotated about a vertical axis through the centre of the grating in the Seya-Namioka mount (Figure 127). A concave grating is used and the... 

Figure 127 Optical diagram of the Seya-Namioka mount...

FIGURE 4-19. Schematic diagram of the Seya-Namioka concave grating spectrometer. [Courtesy McPherson Instrument Corp.]... 

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