Three-body reaction rate in spin-polarized atomic hydrogen

Isaac F. Silvera, Jook T. M. Walraven

J. M. Yuan, T. K. Lim

Studies on the stability of spin-polarized atomic hydrogen against collisional quenching are briefly reviewed. Previous work reveals the importance of the three-body recombination reaction as a destructive mechanism. An order-of-magnitude estimate of this three-body reaction rate made previously leads to a maximal stable density equal to 1017 atoms/cm3 for a duration of a day. A discussion of approximations used suggests that the real density could be a couple of orders of magnitude higher.

Andrei E. Ruckenstein

D. A. Bell, Harald F. Hess, Greg Kochanski +5 more

We have studied relaxation and recombination processes in compressed, doubly polarized atomic hydrogen at temperatures from 0.13 to 0.60 K and magnetic fields from 3 to 9 T. The gas and surface dipole three-body recombination rate constants at a field of 7.6 T are measured to be, respectively, ${L}_{g}$=8.9(8)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}39}$ ${\mathrm{cm}}^{6}$ ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$ and ${L}_{s}$=1.2(4)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}24}$ ${\mathrm{cm}}^{4}$ ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$. They decrease slowly with field and ${L}_{s}$ exhibits no significant angular dependence. The three-body recombination rate due to hyperfine mixing has also been measured. Electronic and nuclear relaxation rates have been measured; the b-c electronic relaxation rate constant in the gas is ${G}^{\mathrm{bc}}$=1.03(7)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}15}$ ${\mathrm{cm}}^{3}$ ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$exp(-${E}_{\mathrm{bc}}$/${k}_{B}$T). The temperature and field dependence of the nuclear relaxation rate in the gas are observed to be in excellent agreement with recent theoretical calculations. Three-body surface recombination-rate measurements using $^{3}\mathrm{\ensuremath{-}}^{4}$He surfaces indicate that as little as one monolayer of $^{3}\mathrm{He}$ on the liquid $^{4}\mathrm{He}$ surface appreciably decreases the adsorption energy of atomic hydrogen. Densities achieved include 4.5\ifmmode\times\else\texttimes\fi{}${10}^{18}$ atoms${\mathrm{?}}^{\mathrm{\ensuremath{-}}3}$ at 0.55 K (pure $^{4}\mathrm{He}$ walls), and 1.4\ifmmode\times\else\texttimes\fi{}${10}^{18}$ atoms${\mathrm{?}}^{\mathrm{\ensuremath{-}}3}$ at 0.19 K (8 at. ? sup 3---He).

Alina Blinova

Three-body association (TBA) of hydrogen is the process by which three hydrogen atoms combine to form a hydrogen molecule and a free atom. The TBA reaction rate is not known precisely, yet its value plays a crucial role in the formation of the first stars. We propose an experiment to measure the TBA of hydrogen using a magnetic field to implode a cloud of atomic hydrogen to achieve high densities. In this work I present the results of a numerical simulation for the idealized case of non-interacting, point-like hydrogen atoms in a hexapole magnetic field. The results show that in this approximation, high atomic densities can be reached. Using existing TBA rate estimates, I show that observation of TBA on short time-scales is feasible with the range of atomic densities available in the proposed experiment. For a more accurate simulation, a closer look at atom-atom interactions and the thermal evolution of the cloud is needed.

B.R. Joudeh