Photoassociation of spin-polarized hydrogen

Using Lyman-alpha spectroscopy we observe photoassociation of spin-polarize d hydrogen atoms to bound vibrational levels of the triplet a(3)Sigma(g)(+) potential. At a density of 10(16) atoms/cm(3) we directly observe light ab sorption and fluorescence in the photoassociation process. The observed lin e positions agree with ab initio calculations to within the precision of pr esent theory. Magnetic sublevels in the photoassociation spectra indicate a n effective internal held which we identify with a nonadiabatic term in the Hamiltonian. We present quantitative models for the magnetic field depende nce of the molecular energy and the photoassociation line shape.