Improved infrared and visible emission spectra of the H3 and D3 molecules

Better-resolved Rydberg–Rydberg emission spectra of the neutral H3 and D3 molecules in the infrared and visible regions, with less interference from H2 and D2 emission, have been obtained by using a Droege–Engelking type of corona discharge source. Using nl (lambda) notation, the lower electronic states are 3p1 in the infrared and 2p0 in the visible, and the upper electronic states are mixed (3s,3p0,3d0,3d1,3d2) states. In particular, a line near 16 842 cm-1 in H3, previously obscured by an H2 line, reveals a (3s,3d) interaction that is confirmed by other lines. The spectra are analysed including this interaction. However, fits to effective Hamiltonians still have relatively large standard deviations, probably partly due to poor convergence of the rotational expansions and partly due to many small perturbations of the levels by background states.