Developments in the measurement of spectral momentum densities with (e,2e) spectrometers

Instrumentation and recent applications of inner-shell electron energy loss spectroscopy of gas phase molecules are reviewed. An overview of recent work in an historical perspective is provided. Comparison is made to the complementary technique of X-ray absorption spectroscopy. Highlights are described of recent applications in: polymer analogue studies, in situ studies of transient species, non-dipole spectroscopy, and systematic measurements of generalized oscillator strengths.