Spectra of rare gas hydrides

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Abstract
Extensive emission bands of KrH and KrD have been observed in the near infrared, visible and ultraviolet regions. Most of them can readily be arranged in Rydberg series with nsσ, npσ, npπ, nd and nf upper states and a 5sσ 2Σ lower state. There is a strong resemblance of the diagram of electronic states of KrH to that of the electronic states of the united atom Rb. The present paper deals with the electronic transitions of KrH and KrD corresponding to the 2 S and 2 P states of Rb. Difficulties (not yet entirely overcome) arise with the nd and nf complexes which will be discussed in later papers of this series. The present paper deals only with the 2Σ and 2Π states arising from ns and np orbitals. The conventional molecular constants have been determined. For most electronic states only v = 0 levels have been observed but in a few cases also v = 1 and v = 2 have been observed from hot bands. No bands with v′ ≠ v″ have been found and thus no reliable vibrational frequencies are obtained. The rotational constants of KrH are very similar in value to those of KrH+ as is to be expected for Rydberg states. As for ArH the line widths of the band lines of KrH involving the lowest 2Σ state is not negligible (0·5 cm-1) indicating predissociation in this 2Σ state. This predissociation is presumably caused (as in ArH) by interaction with the repulsive ground state arising from ground state Kr + H. It is however distinctly less strong than in ArH. Indeed in KrD (unlike ArD) line broadening by predissociation is undetectable.

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