Compression experiments with spin-polarized atomic hydrogen

Doubly polarized hydrogen has been produced up to densities of 2×${10}^{18}$ ${\mathrm{cm}}^{\mathrm{-}3}$ with the use of a compression technique. Samples were compressed up to five orders of magnitude into small bubblelike volumes under a column of liquid helium. This technique enabled us to study the volume decay of a bubble at almost constant gas density for minutes. The analysis of the volume decay of such a bubble is discussed. A bulk three-body recombination process was observed with rate constant $C_3$=[7(2)]×${10}^{\mathrm{-}39}$ ${\mathrm{cm}}^6$ ${\mathrm{s}}^{\mathrm{-}1}$, as well as bulk electronic b→c relaxation with rate constant $G_{\mathrm{bc}}^v$↓=[12(4)]×${10}^{\mathrm{-}16}$ ${\mathrm{cm}}^3$ ${\mathrm{s}}^{\mathrm{-}1}$. The nature of the three-body process is analyzed with a set of extended rate equations. The samples were very delicate and rapid compressions could result in explosions.