The band spectrum of lanthanum monoxide

The spectrum has been observed from λ 8700 to λ 2850, and the band-heads (most of them not hitherto recorded) arranged into several systems. While the work was in progress Auerbach* gave high dispersion data for some of the new infra-red heads, and Mecke dagger briefly reported the analysis of seven systems, having o, o bands at (1) λ 4372; (2) λ 4418; (3) λ 5600; (4) λ 7380; (5) λ 7404; (6) λ 7877; and (7) λ 7910. Mecke concluded that ( a ) systems 3, 5 and 7 have a common final state; ( b ) so have systems 1 and 2; and ( c ) the initial states for 1 and 2 appear to be the final states for 4 and 6 respectively. The author's analysis of 2 differs from Mecke's, the 1, 2 band in the former being the 0, 1 band in the latter. Hence, while Mecke's conclusion ( a ) is approximately confirmed, ( c ) becomes untenable if ( b ) is true, as it probably is. If systems 1 and 2 have states in common with 4 and 6 respectively, they must be the final states in each case. Systems 4 and 6 resemble one another in appearance and in initial and final vibrational frequencies, but probably have no state in common. They may represent the R heads of two systems of which 5 and 7 respectively are strong Q heads; the pair of systems (Δν e = 864 cm. -1 ) having a common final state and corresponding to the infrared 2 P -> 2 S doublet of Cs (Δ 2 P = 554 cm. -1 ); but there appears to be evidence against this interpretation. Some ultra-violet bands, λ 3710 - λ 3457, degraded towards shorter wave-lengths, i.e. opposite to those of systems 1... 7, have been measured. Eight of these appear to belong to an incompletely traced eighth system due to a transition from the final state of one or more of the above systems, e.g. 3, 5, 7, to the initial state of another, e.g. 1 or 2. Appendix . A brief note is given on the general theory of electronic band spectra of diatomic molecules.