Zero Field Level Crossing in Excited States of Molecular Hydrogen

Zero field level crossing effects have been observed in the lines emitted from the J = 1, 2, and 3 rotational levels of the [Formula: see text] state of molecular hydrogen excited in an r.f. discharge. The polarization of the R(0), R(1), and R(2) lines of the 3d 1 Σ → 2p 1 Σ(0 → 0) band as a function of magnetic field was observed to be Lorentzian, and using the Landé g factors measured by Dieke et al. yields radiative lifetimes of 2.66 × 10 −8 s, 3.83 × 10 −8 s, and 3.93 × 10 −8 s for J = 1,2, and 3 respectively. The half-width of the level crossing curves was observed to vary linearly with pressure in the range 15 m Torr to 90 m Torr and yield collision cross sections of [Formula: see text] for all three states. The source of the discrepancy between the first and the latter two lifetimes is discussed. The lifetime of the J = 2 1 , 3d 1 Π state has also been measured with less precision and yields 3.84 × 10 −8 s.