The electronic isotope shift in the Lyman bands of H2, HD, and D2

Abstract

Five absorption bands in the [Formula: see text] transition of each of the molecules H2, HD, and D2 were obtained under high resolution in the 1050–1130 Å region in order to determine precise values of the electronic energy (Te) and the change (ΔTe) upon isotopic substitution. The fifth order of a 21-ft concave diffraction grating was employed. The experimental results are Te(H2) = 91 699.54 cm−1, Te(HD) = 91 698.88 cm−1, and Te(D2) = 91 698.83 cm−1. These reveal a surprisingly small shift (< 1 cm−1 in ΔTe) and show that the electronic energies (Te) are in remarkably close agreement (5.4–7.8 cm−1) with ab initio calculations.