Asymmetry of field-induced shape resonances in hydrogen

Asymmetric resonance profiles observed in H atoms in a strong electric field are derived analytically. The most significant deviations from a Lorentzian line shape, H/sup F/ = ..gamma../(scre/sup 2/+..gamma../sup 2/), occur for resonances near the top of a potential barrier. Parametrization as a Fano profile is inappropriate. The line-shape formula, a Lorentzian with energy-dependent reduced width ..gamma../sub Q/(scre) = ln(1+Q(1-Q)/sup -1-s/cre)/ln(( 1-Q)/sup -1/), depends on a single asymmetry parameter Q (0