The existence of marked structure in the 2- to 5-eV energy spectra of near-earth ionospheric photoelectrons has been predicted by theory and observed by experiment. This structure, arising from resonant vibrational excitation of N2, is seen as a valleylike dip in the spectra near 2.5 eV and is predicted to be most prominent at low altitudes (110 km), then to diminish with incresaing altitude until it disappears in the 200- to 250-km region. All measurements to data indicate that the overall magnitude of this valley or dip is significantly less than that predicted by theory, but confirm a trend toward diminishing prominence with increasing altitude above about 150 km. Below 140--150 km, however, the valley is observed in the present measurements include the only observations, to our knowledge, of this spectral structure below 140 km, and these indicate that its maximum prominence occurs to the 140- to 150-km altitude region, below which it is consistently observed to decline rapidly in magnitude. Recent refinement of theory may lead, in part, to an explanation of these discrepancies. The experimental results are summarized and the difficulties peculiar to space vehicle measurements of very low energy ambient electrons are examined.