Spectra of the rare gas hydrides. IV. Three new bands of argon deuteride involving a low-lying ‘‘p’’ Rydberg state

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Abstract
Three fairly strong emission bands of ArD at 6100, 6900, and 10 200 cm−1 have been studied at high resolution. They show very different structures: the first exhibits only Q‐form branches, the second P, R, O, and S‐form branches, and the third Q, S, and O‐form branches. The rotational analysis of each of these bands is not trivial, mainly because the upper state of the first which proved to be also the lower state of the second and third is strongly affected by l uncoupling [i.e., transition to Hund’s case (d)] and as a result the usual method of combination differences cannot be applied in their analysis. However, more sophisticated combination differences have been found between the three bands which lead to unambiguous assignments of rotational quantum numbers and thus to rotational constants. It was found that the upper state of the 6100 cm−1 band can be most conveniently represented as a p(2Σ,2Π) complex. This assumption, together with the theoretical selection rules for such a case, led to a full understanding of the structure of the three bands.