Fig. 1: Energy levels of \({{\bf{H}}}_{{\bf{2}}}^{{\boldsymbol{+}}}\) and transitions relevant to this work.
a, The lowest three rotational levels of the vibrational states v = 0–3. The studied transition (v = 1, N = 0) → (v′ = 3, N′ = 2) is shown by the black arrow, whereas the dissociation radiation is indicated by the orange arrow. b, Spin (left) and Zeeman structure (right) of the two rovibrational levels addressed in the present study. The upper vibrational level v′ = 3 consists of two states F′ = 3/2, 5/2 that are split by 86.8 MHz by the interaction between rotation and the magnetic moment of the electron. The two unperturbed spin components fa and fb of the transition are shown in purple and brown, respectively. The spin-averaged transition frequency fspin-avg is not directly measured, but is indicated schematically as a black-dashed arrow. On the right side, the Zeeman splittings are shown for the nominal field applied during spectroscopy, BREMPD = 7.14 μT. To show the Zeeman splitting, the vertical axis is broken at two positions. On the far right, the three coloured arrows (blue, green and red) indicate the measured Zeeman components \({f}_{{a}_{1}}\), \({f}_{{b}_{1}}\) and \({f}_{{b}_{2}}\). F and F′ are the total angular momentum of the molecule, mF is the total angular momentum projection quantum number.
