G+K 1Σ+g double-minimum excited state of H2

Abstract

We have obtained a Born–Oppenheimer potential curve for the previously uncharacterized third ¹Σ⁺_g state of H₂, using a correlated 20‐term wavefunction of generalized James–Coolidge type. We find this potential curve to have a double‐minimum character, with the inner (Rydberg‐like) and outer (’’ionic’’) wells having minima at about 1.99 and 3.30 bohr, respectively, and an intervening maximum at 2.76 bohr. Unlike the extensively studied E+F double‐minimum state, the outer well here appears to be the deeper, by some 450 cm⁻¹ in our calculation. The inner and outer minima can apparently be associated with spectral lines that in experimental tables have previously been attributed to distinct G and K electronic states. The appropriate spectroscopic term symbol of this combined state is accordingly G+K ¹Σ⁺_g (1sσ3dσ+2pπ²).