Maomao Gong

Fragmentation dynamics of carbonyl sulfide in collision with 500 eV electron

The fragmentation dynamics of OCSq+ (q = 2, 3, 4) induced by electron collision at an impact energy of 500 eV is studied. By using the momentum imaging technique, the three dimensional momentum vectors of all the fragments are obtained, which enables us to analyse both the kinetic energy release and the momentum correlations for a certain fragmentation channel. Up to fifteen dissociation channels are analyzed including six, five, and four channels for two-body, and incomplete and complete three-body Coulomb fragmentations. For three-body dissociation, the fragmentation mechanisms are investigated with the help of Dalitz plot and Newton diagram. It is found that the sequential fragmentation involves in OCS2+→O+C++S+ with S+ emitted first and in OCS3+→O++C++S+ with O-C and C-S bonds breaking first. The remaining channels, however, always dissociate through a concerted mechanism. The relative intensities of the channels are also presented in this work.

Imaging molecular geometry with electron momentum spectroscopy

Electron momentum spectroscopy is a unique tool for imaging orbital-specific electron density of molecule in momentum space. However, the molecular geometry information is usually veiled due to the single-centered character of momentum space wavefunction of molecular orbital (MO). Here we demonstrate the retrieval of interatomic distances from the multicenter interference effect revealed in the ratios of electron momentum profiles between two MOs with symmetric and anti-symmetric characters. A very sensitive dependence of the oscillation period on interatomic distance is observed, which is used to determine F-F distance in CF4 and O-O distance in CO2 with sub-Ångström precision. Thus, using one spectrometer, and in one measurement, the electron density distributions of MOs and the molecular geometry information can be obtained simultaneously. Our approach provides a new robust tool for imaging molecules with high precision and has potential to apply to ultrafast imaging of molecular dynamics if combined with ultrashort electron pulses in the future.

Note: A high-efficiency multi-coincidence method designed for molecular fragmentation studies

A high-efficiency multi-coincidence method is developed based on the hardware electronic multiple coincidence units. The multi-hit signals originating from one single detector can be selected and measured in coincidence. The performance of the method is tested by the electron impact three-body fragmentation of CO2(3+). Compared to the conventional method, the relative and absolute coincidence efficiencies of the triple-coincidence measurement are improved by about 200 and 3 times, respectively.

Multi-center interference effect on (e, 2e) electron momentum spectroscopy

The multi-center interference effect of three outermost molecular orbitals (MOs) of CF4 is investigated using (e, 2e) electron momentum spectroscopy. We show that the observed oscillations are directly informative of the nature of molecular structure. By fitting the experimental results, the bond length of F-F of gas phase CF4 is determined.

Non-sequential and sequential fragmentation dynamics of OCS3+ in collision with 500 eV electron

Non-sequential and sequential fragmentation dynamics of OCS3+ investigated by electron collision at impact energy of 500 eV is reported in this abstract. By using Dalitz plot together with momentum correlation spectrum various dissociative channels are distinguished.

Three-body fragmentation dynamics of CO2q+ (q = 3, 4) induced by electron collision at 500 eV impact energy

Electron impact induced three-body fragmentation of CO2q+ (q = 3, 4) is investigated. For CO23+, non-sequential and sequential fragmentation processes are observed. For CO4+2, however, only non-sequential fragmentation processes are observed. The momentum correlations of each dissociative channel is analyzed by Newton diagram.