Helium surface electron attachment to atomic hydrogen in applied magnetic field

We measured reaction rates of electron attachment to atomic hydrogen on liquid helium surface at 0.3 K in applied magnetic fields up to 11 T. The lifetime of electron-hydrogen gas in two-dimensional mixture becomes longer as the magnetic field is increased. It is found that the reaction rate coefficient behaves like ∼B^-2 and its value above 5 T is eight orders of magnitude smaller than the zero field value. We interpret our result that only electron spin singlet collisions produce negative hydrogen H^-. It is consistent with the fact that the two bound electrons of H^- are spin antiparallel.