Transmission Properties of a LiF–O2 Filter for Radiation Resulting from Electron Impact on H2: Cross Sections for Lyman-α Radiation

Abstract

In many experiments Lyman-α radiation has been detected by means of the iodine-vapor-filled ultraviolet photon counter of Brackmann, Fite, and Hagen in combination with a LiF–O2 filter. In the case of electrons incident on molecular hydrogen, Fite and Brackmann have used the detector for determination of the cross section for ``countable ultraviolet radiation'' (cuv) being chiefly composed of Lyman-α radiation and an unknown fraction of molecular radiation. In the present investigation the transmission properties of the LiF–O2 filter are investigated. At 100 eV impact energy it is found that 26% of the transmitted radiation is molecular radiation. Considering this fraction, it is possible to evaluate the cross sections for Lyman-α radiation from Fite and Brackmann's cuv cross sections. These cross sections agree very well (within about 6%) with those of de Heer and Carrière, obtained by a different procedure.

Laboratory studies of collisions of energetic H+ and hydrogen with atmospheric constituents

“…The transmission function for the most transparent 02 window, centered at 121.6 nm, has a, fullwidth, half-maximum transmission of approximately 0.3 nm and, fortuitously, is nearly a maximum at Lyman , [Clark and Metzger, 1969]. The primary advantages of this technique are the high transmission, simplicity, and low cost of the filter; the primary disadvantages are the potential transmission of features other than La [Carrigre and de Heer, 1972] and the relatively narrow bandwidth of the filter. When L,a is detected at the magic angles, the Doppler shift of L, from fast H •* is substantial in comparison to the bandwidth of the filter, and hence the transmission suffers.…”