Absorption Coefficients of Helium between 599 and 610 Å; Transition Moment for He2 A1Σu+←X1Σg+

Abstract

Absorption coefficients of helium have been measured in the region of the continuum‐bound transition $A^1{\Sigma }_u^{+}{\mathrm{\leftarrow X}}^1{\Sigma }_g^{+}$ of He₂ (599–610 Å) for temperatures of 77, 200, and 298°K. The absorption coefficient k is proportional to the square of the helium density n². The quantity k/n², ranging between 10⁻³⁹ and 10⁻⁴² cm⁵, is in excellent agreement with the continuum‐bound absorption coefficients of He₂ $\mathrm{A\leftarrow X}$ calculated by Sando and Dalgarno, supporting a value of 0.20 a.u. for the electronic transition moment of He₂ $\mathrm{A\leftarrow X}$ between 2 and 3 Å.