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Emission
spectrum of an ultraviolet deuterium arc lamp showing characteristic hydrogen
Balmer lines (sharp peaks at 486 nm and 656 nm labelled D
β and D
α from left to right respectively), continuum emission in the ~160-400 nm region and Fulcher band emission between around 560 to 640 nm. The emission spectrum of deuterium differs slightly from that of
protium due to the influence of
hyperfine interactions, though these effects alter the wavelength of the lines by mere fractions of a
nanometer and are too fine to be discerned by the
spectrometer used here.
A deuterium arc lamp or simply deuterium lamp is a low pressure gas discharge light source often used in spectroscopy when a full spectrum (continuous) source of illumination in the ultraviolet region is needed. The origin of the continuum ultraviolet radiation which extends from around 160 nanometers to 400 nanometers arises not from the relatively simple process of decay of atomic excited states ("atomic emission") but instead from "molecular emission" processes, where radiative decay of excited states, in this case of molecular deuterium (D2) cause the effect. This effect is somewhat analogous to the visible light continuum molecular emission of sulfur lamps.
