The 2535.52ik (zs0--aP1) line of mercury is observed in absorption in the presence of helium compressed up to 1500 arm. Line shape, oscillator strength, shift and halfwidth of the line are measured as a function of the density of helium. The line shifts towards the violet and broadens asymmetrically with increasing helium density, developing a pronounced shoulder about 14/~ from the main peak, on the violet side. The observed ratio of half-width to shift (5,1 at low densities) disagrees with the prediction based on Lindholm's theory of pressure broadening with Van der ~vVaals interactions. With repulsive (R -12) interactions only, the Lindbolm theories gives rough agreement. On the other hand, the statistical theory of Margenau can qualitatively explain the occurrence of a shoulder. The oscillator strength decreases rapidly with increasing density. ยง 1. Introduction. The purpose of the experiments described here was to obtain information on the c h a r a c t e r of the interaction of Hg, in ground as well as in excited states, with foreign gas atoms. Studies of such interactions b y m e a s u r e m e n t s of the broadening of the 2536.52 A m e r c u r y resonance line h a v e been reported in the literature:
Enfission s p e c t r u m : There h a v e been some m e a s u r e m e n t s of emission f r o m w e a k l y ex cited m e r c u r y v a p o u r with v e r y low helium pressures (below 1 atm. lb)le)).
Absorption s p e c t r u m : Precise m e a s u r e m e n t s in absorption on the m e r c u r y resonance line are described b y F t i r c h t b a u e r , J o o s and D i n k e la c k e r 1~), with A, C02, H2, N2 and H 2 0 as broadening gases, at pressures up to 50 a t m . T h e work of R o b i n with A, N2, H2 and He which extends up to 1500 atm. is of a m o r e qualitative character la)le~lfL Absorption measurem e n t s h a v e also been p e r f o r m e d in the Van der W a a l s -l a b o r a t o r i u m with argon, nitrogen a n d neon.
This publication deals with experiments on the effect of helium at pressures up to 1500 a t m . on the m e r c u r y resonance line in absorption. The a p p a r a t u s is described in ยง 2, m e a s u r e m e n t s in ยง 3, the results a n d an estimate of their a c c u r a c y in ยง 4. A theoretical discussion follows in ยง 5.