Bond compression of V-H-V shows the electron transition from n=1 to n=0, smaller hydrogen is created by V-H-V bond compression
Bond compression of D-D can cause the higher electron transition probalbility due to the mechanical stress to have very long time to keep the D-D distance snaller.
This is the mechanism of Cold fusion meaning that it is not easy to have such elecrtron transition by nuclear reaction experiment.
However there used to be a buffer energy fusion reactor with the nuclear reaction.
The authors explained that in case that hydrogen ion beam energy lower than 30keV and Li target is melted, abnormal heat generation of 1013times greater than the theoretical nuclear fusion theory.
 Hidetsugu Ikegami and Roland Pettersson,Evidence of enhanced non-thermal nuclear fusion, bulletin of institute of chemistry, Uppsala University,2002 http://uu.diva-portal.org/smas…iva2:52651/FULLTEXT01.pdf
Hydrogen ions are implanted directly from nonthermal discharge plasma or ion source into a surface of liquid Li metal at a buffer energy of a few tens keV where nuclear stopping occurs. The ions interact with Li atoms or mixed element atoms which are not being internally excited and tend towards the formation of united atoms at the minimum Gibson free energy point. This leads to the enhanced rate of non-thermonuclear fusion of hydrogen ions due to cohesion in the liquid metal.
The authors argued the new scheme of buffer energy nuclear fusion in Liquid Li metal. Semi-classical treatments on the fusion rate have also been presented on the basis of Arrhenius equation. The mechanism of rate enhancement caused by the united atom formation under cohesion in the liquid metal are essential for leading to practical nuclear fusion and further systematic investigations are required.
E-CAT has used the same reaction as buffer energy fusion.
Thus E-CAT need to have the Li-H compression with particle collision.
The authors argue in ref  that a major source of energy is a reaction between the first excited-state of Li-7 and a proton, followed by the breakdown of Be-8 into two alphas with high kinetic energy, but without gamma radiation. The unusual property of the Li-7 isotope that allows this reaction is similar to the property that underlies the Mossbauer effect
Authors use the lattice version of the independent-particle model (IPM) of nuclear theory to show how the geometrical structure of isotopes indicate nuclear reactions that are not predicted in the conventional version of the IPM.
Authors speculate on similar mechanisms that may be involved in other low-energy nuclear reactions (LENR).
E-CAT uses the nuclear reaction of 7Li + 1H, which is the same nuclear reaction of 7Li+1H=>8Be*=>24He+17.3MeV as is used by Buffer Energy Nuclear Fusion in ref , so the both are based on the same mechanism of hydride bond compression and Buffer Energy Nuclear Fusion has the mechanism of bond compression by ion beam.
Thus, I develop the mechanism theory for this reaction based on H-Li bond compression as is in Fig.15. The Li has hydride bond is Li-H so the compression of Li-H can create the neutron (tightly bound proton and electron pair), so I agree the argument of authors that a major source of energy is a reaction between the first excited-state of Li-7 and a proton, which is actually neutron, which is the small hydrogen (tightly bound proton-electron pair) created by Li-H bond compression which is explained in ref.
But note that this reactor has no mechanism of bond compression, so it can be very difficult to trigger cold fusion.
OR mechanical stress directly by the metal plates.
in Fig25 mechanical stress to be applied by the 2 metal plate, and distance adjustment by Fig24 can have the stronger(faster) speed of nano-particle of Li-H by ultrasonic oscillator.
OR Li-H thin film to be compressed by the mechanical stress.
This mechanical stress works on NASA Lattice Confined Cold Fusion of Er-D.