  We show that deep inelastic neutron scattering from hydrogen(or other light
nuclei) can be used to measure a spectrum of anharmonic contributions to the
target atom momentum distribution with high and known accuracy . The method is
applied here to determine the momentum distribution of the hydrogen in the
hydrogen bonded system KHC2O4(potassium binoxalate), where 13 anharmonic
coefficients are obtained at the 2-sigma to 3-sigma level. The momentum
distribution is obtained to an accuracy of better than few percent at all
significant values of momentum.
