Hunds coupling case e

Notice that in both case (d) and case (e) there is no molecular projection quantum number. An example of case (e) coupling, probably the first, has been observed [60] for vibration rotation levels of the HeKr+ ion which lie very close to the dissociation limit. The Kr+ atomic ion has L = 1 and S= 1/2, so that. Ja is 3/2 or 1 /2, and the spin orbit interaction is strong. When a very weak bond is formed with a He atom,. Ja remains a good quantum number, at least for the most weakly bound levels, but there are nevertheless series ofrotation levels, with rotational energy BR(R + 1). The details are described in chapter 10, where we show that case (e) coupling is identified, both by the observed pattern of the rotational levels, and by the measured Zeeman effects and effective g factors for individual rotational levels. 

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