Molecular vibrational spectroscopy by inelastic x-ray scattering: Experimental determination of the absolute vibrational cross section in liquid nitrogen

Inelastic x-ray scattering (IXS) is used to measure the vibrational spectrum of liquid nitrogen at a temperature of 76 K and a pressure of 1 bar as a function of wave vector q in the $1.45\char21{}11.8 {\mathrm{A}}^{\ensuremath{-}1}$ range. The absolute IXS cross section for the vibrational excitation is determined in the explored q range. Its comparison with a theoretical calculation is very satisfactory, and leads to a precise determination of the intramolecular distance and the vibrational root-mean-square displacement. This demonstrates that the IXS technique can provide accurate information on the vibrational dynamics in molecular systems. The peculiarities of IXS with respect to other vibrational spectroscopies are briefly discussed.