The inelastic scattering of cold neutrons by methane and ammonia

The inelastic scattering of cold neutrons by gaseous methane and ammonia has been investigated to test the accuracy of the theories of neutron scattering by molecules. The experimental results at small scattering angles, corresponding to small neutron momentum transfers, show separate peaks due to translational and rotational motions of the molecules, demonstrating the shortcomings of the Krieger-Nelkin theory. Agreement with Griffing's theory assuming discrete rotational levels is good at high scattering angles, but at the lowest angles there is a small discrepancy between the theoretical and measured heights of the translational and rotational peaks.