A sequence of absorption or emission lines in the far-infrared part of the spectrum, due to hydrogen. They are caused by electron jumps between the fifth energy level and higher levels. Pfund-α is at a wavelength of 7.46 μm, and the spacing between the lines diminishes as they converge on the series limit at 2.28 μm. The series is named after the American physicist (August) Herman Pfund (1879–1949). See also hydrogen spectrum.
Subjects: Astronomy and Astrophysics.