While it is well appreciated that electron simulated desorption ion angular distribution (ESDIAD) measurements contain information about chemical bond directions at surfaces, it is also known that the lateral momentum of the adsorbate must influence the ESDIAD patterns. We present, for the first time, energy resolved ESDIAD patterns which allow one to measure the anisotropy in the lateral momentum of the chemisorbed species. Using a new method, momentum-resolved ESDIAD patterns are acquired in narrow kinetic energy windows by time-of-flight selection. For CO chemisorbed on Cu(110), the excited neutral CO* species exhibits an elliptical pattern at low kinetic energies with the major axis of the ellipse in the [1(1) over bar0$] azimuthal directions. For increasing CO* kinetic energies, the ellipticity decreases, and at very high kinetic energies, the ellipticity changes to the [100] azimuth. These observations, together with the temperature dependence of the pattern shape over the range 32-180 K, yield information about the frustrated translational energy of the adsorbed molecule, and permit a qualitative assessment of the shape of the potential energy well governing the adsorbate’s librational motion.