Abstract
The measurement of the rotational energy levels of H+2 (X 2Σ+g) for v=0–7 on ordinary hydrogen at room temperature is reported. The transitions are directly observed by means of a newly developed threshold electron analyzer which has an observed resolution (FWHM) of 0.003 eV and for which, unlike previous analyzers, the transmission probability goes identically to zero for energetic electrons. The molecular constants obtained are in agreement with values obtained via Rydberg series extrapolations and with theory. The adiabatic ionization potential of hydrogen was determined to be 124 424±9 cm−1.