Pressure-enhanced ortho-para conversion in solid hydrogen up to 58 GPa

Proc Natl Acad Sci U S A. 1999 Oct 26;96(22):12269-72. doi: 10.1073/pnas.96.22.12269.

Abstract

We measured the ortho-para conversion rate in solid hydrogen by using Raman scattering in a diamond-anvil cell, extending previous measurements by a factor of 60 in pressure. We confirm previous experiments that suggested a decrease in the conversion rate above about 0.5 GPa. We observe a distinct minimum at 3 GPa followed by a drastic increase in the conversion rate to our maximum pressure of 58 GPa. This pressure enhancement of conversion is not predicted by previous theoretical treatments and must be due to a new conversion pathway.