HYDROGEN MOLECULE IN A STRONG PARALLEL MAGNETIC-FIELD

We investigate the hydrogen molecule in a strong parallel magnetic fie ld using a fully numerical Hartree-Fock approach. We find that for mag netic fields below 4.2 x 10(4) T the ground state of Hz is the strongl y bound singlet state (1) Sigma(g), for magnetic fields stronger than 3 x 10(6) T the ground state of the molecule is the strongly bound tri plet (3) Pi(u), and for magnetic fields between 4.2 x 10(4) T and 3 x 10(6) T the symmetry of the ground state is the triplet state (3) Sigm a(u), which is characterized by repulsion at intermediate internuclear distances and by a weak quadrupole-quadrupole interaction between ato ms at large internuclear separation. In this region of magnetic field strength the hydrogen molecule is bound weakly, if at all; the hydroge n atoms behave like a weakly nonideal gas of Bose particles and can fo rm a superfluid phase predicted in earlier works [Korolev and Liberman , Phys. Rev. Lett. 72, 270 (1994)]. For magnetic fields between approx imate to 3 x 10(5) T and 3 x 10(6) T the triplet state (3) Pi(u) is fo und to be metastable. This state may be responsible for an unknown exc itonic line observed experimentally [Timofeev and Chernenko, JETP Lett . 61., 617 (1995)].