title: New ortho-para conversion mechanism in dense solid hydrogen.
abstract: Analysis of recent measurements of striking changes in the rate of ortho-para conversion of solid H(2) up to 58 GPa shows that the conversion mechanism must differ from that at ambient pressure. A new conversion mechanism is identified in which the emerging excitations are coupled to the converting molecules via electric quadrupole-quadrupole rather than nuclear spin-spin interactions. The latter only initiates conversion while the coupling enhancement associated with the new mechanism is ensured by high compression and a gap closing, with the conversion energy diminishing strongly with increasing pressure.
authors.affiliation: Geophysical Laboratory and Center for High Pressure Research, Carnegie Institution of Washington, 5251 Broad Branch Road, NW, Washington, D.C. 20015, USA.
authors.forename: M A
authors.initials: MA
authors.lastname: Strzhemechny
authors.forename: R J
authors.initials: RJ
authors.lastname: Hemley