Abstract

THE beryllium arc in a hydrogen atmosphere emits two band systems—one in the green region at 4800-5120 A., and the other one in the ultra-violet from `3700 and extending as far as can be reached by quartz optics. Very recently both band systems have been measured and analysed by W. W. Watson (Phys. Rev., 32, 600; 1928), and independently of this, M. Petersen (Phys. Rev., 31, 1130; 1928) has given a short account of the green system. Both investigators state that this system belongs to an electronic transition 2P2S of beryllium hydride, thus apparently corresponding to the long set of well-known band systems emitted by hydrides of magnesium, calcium, zinc, cadmium, and mercury. The ultra-violet system was analysed by Watson only in the region `3700-2700 and thus permits no definite statements regarding the pure electronic transition, n′ = n″ = 0, which falls below e2700. However, as pointed out by Watson, the investigation of the band n′ = nPrime; = 0 is necessary for information regarding the origin of the ultra-violet system. Watson hesitates between two alternatives: the ultra-violet system emitted by beryllium hydride having a common final state with the green system 2S2S, or belonging to an ionised BeH+ molecule, the transition being of the type 1S1S.

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