Accurate ab initio rovibronic spectrum of the X 1Σg+ and B 1Σu+ states in Ar2

Using recently developed coupled-cluster response methods, accurate potential curves for the ${\mathrm{X\hspace{0.17em}}}^1{\Sigma }_g^{+}$ and ${\mathrm{B\hspace{0.17em}}}^1{\Sigma }_u^{+}$ electronic states of ${\mathrm{Ar}}_{\mathrm{2}}$ are evaluated and the lowest rovibronic energy levels are calculated. The results are in very good agreement with the experimentally available spectroscopic data, and suggest a reassignment of the experimental vibrational numbering in the ${\mathrm{B\hspace{0.17em}}}^1{\Sigma }_u^{+}$ state.