ABSTRACT
INTRODUCTION Capillary-arc spectral lamps using the emission of hydrogen or deuterium dissociation continua are known to be widely used in spectroscopy and analytical instrumentation as rather convenient sources of UV and VUV continuum radiation. Nowadays such lamps are characterized by aperture diameters of typically 0.5mm, whereas the shape of the central plate carrying the aperture could differ distinctly. Analyzing the intensity distribution of the dissociation continua we found that their radial profiles exhibit structures in the wings, e.g. in the subset of figure!. The amplitude and shape of these symmetrical features depend on the type of the aperture built-in inside the lamp. The dissociation continuum of hydrogen molecules and their isotopes can be used not only to estimate the total dissociation rate, it is also possible to characterize via the relative intensity distribution the vibrational population distribution of the ground state [1]. This method was applied to the continuum emission of deuterium measured at several radial positions in different deuterium lamp types and for different anode currents. As a result, also the vibrational temperature exhibits a radial distribution indicating locally varying excitation conditions for the molecules. Because the latter depend also on the electron density and their velocity distribution, the result is interpreted as a link to space charge constellations in front of the cup structure. This indicates a possible explanation of the radially structured emission profiles.
