Potential Curves from Molecular Continuum–Continuum Emission. II. The Dissociation Energy of He2 A1Σu+

The 600‐Å bands of ⁴He₂ were reinvestigated photoelectrically, and the pressure, temperature, and wavelength dependence of the oscillatory structure in the region of 602 < λ < 710 Å were determined. The analysis of the previous paper was applied to yield the potential curve of He₂ $A^1{\Sigma }_u^{+}$ in the range $\text{1.5\hspace{0.17em}<\hspace{0.17em}R\hspace{0.17em}<\hspace{0.17em}2.4 Å}$ . Combination of these data with published visible spectroscopic results on this state lead to a dissociation energy $D_e{\mathrm{(A}}^1{\Sigma }_u^{+}\text{)\hspace{0.17em}=\hspace{0.17em}2.55\hspace{0.17em}±\hspace{0.17em}0.17}\mathrm{eV}$ . The position and height of the maximum in the potential at large $R$ have been determined as 3.0 ± 0.3 Å and 0.03 ± 0.03 eV, respectively. The $\mathrm{A–X}$ electronic transition moment is shown to depend only weakly on $R$ in the range $\text{1.7\hspace{0.17em}<\hspace{0.17em}R\hspace{0.17em}<\hspace{0.17em}2.15 Å}$ .