The “binuclear atom”– has been known but ignored since the early days of LENR. 1991 to be exact. It is metastable, and that could be part of the problem.
The metastability of the binuclear atom could disappear in a host matrix temporarily, and additionally could supply fast ions on decay - even without nuclear fusion. More recently, there has been ongoing speculation about getting deuterons close enough (naturally by a densification process) so as to benefit from the strong force, in order to facilitate fusion. Protons are known to pair naturally, but as it turns out – way back in 1991 in an overlooked paper, the exact modality was clearly identified and with some formalism – the binuclear atom. There are several theories of dense hydrogen which may or may not depend on nucleon pairing, but this one – possibly the best one - has been ignored until recently. In fact was not published online for 17 years after it was presented. http://aip.scitation.org/doi/abs/10.1063/1.40685?journalCode=apc “(D+D+)2e− binuclear atoms as activated precursors in cold and warm fusion” AIP Conference Proceedings 228, 668 (1991); https://doi.org/10.1063/1.40685 By G. F. Cerofolini and N. Re Here is a piece on nucleon pairing: https://physics.aps.org/synopsis-for/10.1103/PhysRevLett.106.252502 More recently, this binuclear atom mechanism of deuteron pairing was revisited by Accomazzi. Paolo Accomazzi in the “ Journal of Condensed Matter Nuclear Science” 25 (2017) 68–75. Available in the LENR-CANR library. This is the latest compilation from Biberian. Amazing to realize that this route for fusion has received so little attention in the past. It can be understood to explain both cold fusion and also Mills and Holmlid, as the author (Accomazzi) implies. Notably Cerofolini and Re were not involved in LENR and moved on to other pursuits - and that detail may indicate why their paper has been overlooked all these years.