Coulomb explosion study for structure analysis of clusters.

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In the present study, molecular targets are multiply ionized by the collision of highly charged atomic ions leading to explosive dissociation of the target molecules. By position sensitive time of flight measurements of the fragment ions, velocity vectors of the fragment ions just after the dissociation were determined. The target molecules studied in these two financial years were N_2, CO,CO_2, and N_2O as typical simple molecules. The summary of the study is as follows.(1) A newly constructed large size anode for position sensitive detection was installed for better collecting efficiency. The performance of the system was examined by measuring recoil ions formed by Ar^<8+>-Ar collisions.(2) Ar^<8+> was collided with N_2 and CO in order to study how the target orientation would affect the charge transfer cross section. The detailed analysis of the fragment ions produced from triply charged diatomic molecules shows that the correlation of angular distribution of ions with Auger electrons would be important. In addition, CO aligned parallel to the incident beam is found to be more favorable for three electron capture.(3) Ar^<8+> was collided with CO_2. The velocity vectors of the two fragment O ions and one C ion for each fragmentation event were determined which will be referred as "Vo1", "Vo2", "Vc", respectively. The histogram of the angle of Vo1 versus Vo2 was consistent with the molecular structure before ionization taking account of the zero point vibrations of bending mode. In addition, the angle of Vo1-Vo2 versus VC was also consistent with the molecular structure. By comparing the results among various fragment channels, "Vo1", "Vo2", "Vc" produced from higher charged states tend to give more proper molecular image of CO_2.(4) Cluster source for the use in the ECR facility was constructed.