Investigations Of Compton Profiles Of H₂and Several Simple Alkane Molecules

Compton profiles of atoms and molecules can reveal the information of the elec-tron momentum density distribution of the ground states and are highly sensitive to the change of the wave functions. Therefore, accurate experimental Compton profile is an important tool to explore the distribution of the electron density of atom or molecule. The experimental Compton profile data with high accuracy can not only explore the electronic structures and the bonding properties but also test the theoretical modes, cal-culational codes, as well as the wave functions of the target strictly. In this thesis, we have measured the Compton profiles of H2and several simple alkane molecules accu-rately using the third generation synchrotron radiation light source. Moreover, we have also calculated the Compton profiles of these molecules by Gaussian09.In this thesis, the mian works and innovations are:(1) The x-ray Compton scattering technique has been realized at the beamline BL15U1of the Shanghai Synchrotron Radiation Facility. The Compton profile of any light atom or molecule can be measured at an incident photon energy of20keV with an energy spread of3eV in the unfocused beam mode. Furthermore, we have designed and built a set of experimental equipments including the gas cell, the silicon drift x-ray detector, the Compton scattering support, etc. The colinear point of the incident pho-ton and the detector’s center line is within0.1mm. It should be pointed out that the gas cell made of aluminium alloy and the two layers design minimize the experimental background greatly;(2) The Compton profile calculation of atoms and molecules has been realized for the first time in our laboratory by Gaussian09. In order to compare the calculated Compton profile with the experimental one, a convolution program has also been made;(3) The Compton profile of molecular hydrogen has been measured, and the statis-tical accuracy of0.2%is achieved near pz=0. The DFT and HF methods with a series of increasing-sized basis sets have also been used to calculate the Compton profiles of molecular hydrogen. The B3LYP calculation is closer to the present accurate measure-ment compared with the HF calculation, which indicates that the electron correlation effect is important to describe the ground state of molecular hydrogen. The good agree-ment of the present experimental result with the DFT calculations in different basis sets indicates that adding the polarization function or the diffuse function is not important for molecular hydrogen;(4) The Compton profiles of molecular methane and ethane have been measured, and the statistical accuracy of0.2%is achieved near pz=0. Since we not only used the advanced synchrotron radiation but also minimized the experimental background, the present experimental Compton profiles of molecular methane and ethane are more accurate than the previous experiments. Furthermore, the DFT calculations also agree with our present experimental results well. By comparing the orbital Compton profiles with their electron density distribution in the position space, a close relationship between Compton profiles and the wave fuctions of the ground states is revealed;(5) The Compton profile of molecular propane has been measured for the first time, and the statistical accuracy of0.2%is achieved near pz=0. The DFT method has also been used to calculate its Compton profile, which agrees with our present experiment very well. Moreover, the comparison between the Compton profile and the electron density distribution in the position space of molecular propane suggests that Compton profiles are highly sensitive to the change of the wave functions.