The pressure effect on the recombination and relaxation of hydrogen atoms in solid hydrogen

We have studied experimentally for the first time the properties of hydroge n atoms in solid hydrogen under pressure. The recombination rate constant h as activation-type temperature dependence in the pressure range from 0 to 2 2 MPa. The activation energy increases linearly with external pressure E-a = (2.4 P + 106 K), as should be expected in the case of a tunneling vacancy mechanism in atom diffusion. Strong pressure effects on the linewidth of t he ESR signal and on the spin-lattice relaxation time T-1 were explained by the competition between the local ortho-para conversion process around the H atom and the pressure-dependent diffusion. (C) 2000 Elsevier Science B.V . All rights reserved.