Penetration of water vapor into some instruments used in the vacuum ultraviolet

Abstract

There is a gradual fall in the t ransmiss ion of a gas fi l ter for isolating the 121.6 nm L c~ line of atomic hydrogen [1]. The cell was evacuated to 3 .10 -6 t o r t , and the absorption spec t rum as a function of time was examined. The loss of t ransmiss ion was due to the gradual accumulation of water vapor. This was established with a se r ies of devices (Fig. 1) consist ing of a cell for absorption analysis 1, which was separa ted by the diaphragm 3 f rom the test space 2. Three se r ies of devices were used. The f i r s t ser ies A had LiF c rys ta l s 5 cemented to the body, while ser ies B had glass 6, and ser ies C had no window. The devices were initially highly evacuated. After some weeks, the eel] volumes w e r e evacuated, and the absorpt ion of the contents was examined with a DVM-1 double-beam vacuum monochromator [2] before and after breaking the diaphram 3 with the hammer 4. Series A and B gave approximately equal water vapor p re s su re s , while ser ies C showed no t races of water. The water thus probably enters via the cement.