C.G. Ning

(e, 2e) electron momentum spectrometer with high sensitivity and high resolution

A high sensitivity and high resolution (e, 2e) electron momentum spectrometer with simultaneous detection in energy and momentum are constructed. The design and performance of the spectrometer are reported. The orbital electron density distributions are obtained accurately and rapidly by using this spectrometer equipped with a double toroidal analyzer. The experimental results on argon and helium exhibit the significant improvements in coincidence count rates, resolution, sensitivity and obtainment of a wide range of adjustable experimental impact energies, which are crucial for further electron momentum spectroscopy studying electronic structure and electron correlation in complex systems.

A multiparameter data acquisition system based on universal serial bus interface for electron momentum spectrometer

A versatile multiparameter data acquisition system based on universal serial bus (USB) interface was designed and has been used on the electron momentum spectromenter. Digitized data were first buffered in a FIFO memory in an event-by-event mode with a check bit, and then transferred to computer through the USB interface. USB interface combined with a microcontroller unit provides much flexibility for data acquisition and experimental controls. The operation performance of the system is demonstrated in the measurement of electron momentum spectra of CH2F2 molecules.

An investigation of valence shell orbital momentum profiles of difluoromethane by binary (e,2e) spectroscopy

The electron binding energy spectra and momentum profiles of the valence orbitals of difluoromethane, also known as HFC32 (HFC-hydrofluorocarbon) (CH(2)F(2)), have been studied by using a high resolution (e,2e) electron momentum spectrometer, at an impact energy of 1200 eV plus the binding energy, and by using symmetric noncoplanar kinematics. The experimental momentum profiles of the outer valence orbitals and 4a(1) inner valence orbital are compared with the theoretical momentum distributions calculated using Hartree-Fock and density functional theory (DFT) methods with various basis sets. In general, the shapes of the experimental momentum distributions are well described by both the Hartree-Fock and DFT calculations when large and diffuse basis sets are used. However, the result also shows that it is hard to choose the different calculations for some orbitals, including the methods and the size of the basis sets employed. The pole strength of the ionization peak from the 4a(1) inner valence orbital is estimated.