Harry - perhaps you should have a look at the work and patents of Haisch and Moddel on the Lamb shift mechanism using hydrogen or helium in Casimir cavities.
The dynamical Casimir effect can be either positive or negative and Lamb shift photons would be cold. IIRC there was a measured cooling effect in some tests - not heating - which is what they wanted. H LV wrote: Now if energy levels below the ground state exist for a hydrogen atom then it may be possible to stimulate the electron-proton pair into this hypo-state, by exposing them to radiation which corresponds to the energy of the photon the pair is expected to release. Harry