No abstract

We investigate the hydrogen molecule in a strong parallel magnetic field using a fully numerical Hartree-Fock approach. We find that for magnetic fields below 4.2ϫ10 4 T the ground state of H 2 is the strongly bound singlet state 1 ⌺ g , for magnetic fields stronger than 3ϫ10 6 T the ground state of the molecule is the strongly bound triplet 3 ⌸ u , and for magnetic fields between 4.2ϫ10 4 T and 3ϫ10 6 T the symmetry of the ground state is the triplet state 3 ⌺ u , which is characterized by repulsion at intermediate internuclear distances and by a weak quadrupole-quadrupole interaction between atoms at large internuclear separation. In this region of magnetic field strength the hydrogen molecule is bound weakly, if at all; the hydrogen atoms behave like a weakly nonideal gas of Bose particles and can form a superfluid phase predicted in earlier works ͓Korolev and Liberman, Phys. Rev. Lett. 72, 270 ͑1994͔͒. For magnetic fields between Ϸ3ϫ10 5 T and 3ϫ10 6 T the triplet state 3 ⌸ u is found to be metastable. This state may be responsible for an unknown excitonic line observed experimentally ͓Timofeev and Chernenko, JETP Lett. 61, 617 ͑1995͔͒.