can , do you happen to know the possible principal quantum numbers of H or D RM?
According to the information above high principal quantum numbers indeed could be causing very high current density levels.
Apparently RM of H or D de-excites quickly and it is typically observed with values of n=1–3 around the "emitter". The lowest energy level is [nowadays] associated with UDH.
RM of K appears to have been typically been observed with considerably higher values (n=40–80 in desorption and 10–20 typically), possibly also due to generally different experimental conditions.
Infrared photons can re-excite RM to high levels, which is also mentioned in Svensson's thesis (screenshot below) and in Holmlid's papers.
Edit: Would it be thinkable that in a relative high principal quantum number could be derived from exiting UDD to D RM and back?
I think that's unlikely according to the explanations provided so far. UDH appears to be associated (change to/from) with the lowest energy form of ordinary RM.
By the way, since it makes little sense to refer to RM without also implying that the azimuthal quantum number ℓ is at its limit (n - 1), i.e. in a circular state, currently RM is referred to by ℓ rather than the special definition of n used years ago.
[...] In RM, the electrons are best described as being in Bohr orbits, with just one good quantum number namely l and having a classical time dependence. This means that n is replaced by l. In the lowest Bohr orbit with radius a0, angular momentum is l = 1.