Dynamics of Three-body Dissociation of Inner-shell Excited Molecules

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In this two-year project, we performed three types of detailed experiments on the ionization and dissociation dynamics of inner-shell excited polyatomic olecules. Two sophisticated apparatus were used which we had introduced on the soft X-ray photochemistry beamline of the third-generations ynchrotron radiation facility Spring-8: a very high resolution photoelectron / Auger electron energy analyzer (SCIENTA) and a multicoincidence ion / electron momentum imaging apparatus (3DTOF).In the first experiment, we used only the ion part of the 3DTOF apparatus to study the dissociation dynamics of three- and four-atomic molecules, such as CO_2, N_2O, and BF_3, and succeeded in detecting three and four fragment ions originating from triply- and quadruply-ionized parent molecules, respectively, in coincidence. The study was highlighted by the separate observation of the two components of the Renner-Teller split Cls→π^* and Ols→π^* excited states. Other highlights were the findings of the bond an … More gle difference at the moment of ionic fragmentation between the N_t (terminal) ls→π^* and N_c (central) ls→π^* excited states of N_2O and of the fact that the inner-shall excited BF_3 molecule changes its Structure from planar to trigonometric pyramidal before the Auger emission takes place.In the second type of experiments, both the electron and ion detectors of the 3DTOF apparatus were used to successfully obtain the electron-ion-ion triple coincidence. The photoelectron angular distributions (PADs) of the fixed-in-space CO_2 molecule could be obtained by taking coincidence measurements among CO^+, O^+, and photoelectron, the momenta of the former two determining the direction of the molecular axis in the three-dimensional space. Variation in the PADs with the excitation energy within the Cls→π^* and Ols→π^* resonance peaks has clearly been demonstrated.The third type of experiment was the very high-resolution resonant Auger spectroscopy using SCIENTA, in which a so-called sub-natural linewidth spectroscopy was aimed at. A highlight was the first observation of multimode excitation in the Ols→2b_2 excitation of the H_2O molecule, i.e., The observation of the progression of the bending vibration in addition to that of the symmetric stretching vibration in the Auger final state. Less