Probing Transition States of Chemical Reactions Utilizing Neutralization of Molecular Ions

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In this project, we intended to probe intermediate or transition state of chemical reactions as directly as possible, by taking four different approaches. The main objective is to establish the technique that utilizes the recombination processes of polyatomic ions to produce temporarily the intermadiate states of neutral rections. In the first approach, we studied the reverse processes to this, that is, the ion pair formation from neutral excited molecules. For this purpose we utilized photoexcitation by synchrotron radiation. The systems we studied include, for example, CH_3X *X^-+CH_3^+, where X is either a halogen atom, H,or D,SO_2*O_-+SO_+, O_-+S_+O.We could successfully obtain a body of important information on the potential energy surfaces leading to ion pair formation, which in turn is relevant to the positive ion-negative ion recombination. In the second approach, a flowing afterglow technique has been used to investigate collisional deactivation of vibronically excited molecul … More ar ions and electronically excited transition metal atoms. Valuable information on the mechanisms, intermediate states, and the relevant rate constants have been obtained for the collisional processes of, for example, CO_+ (A^2II,v), N_2O^+ (A^2SIGMA, v), Ti (a^3F,a^5F), and V (a^4F,a^6D). In the third and fourth approarch, we started with designing and constructing a beam-chamber/cressed beams apparatus with three types of ion sources for generating high intensity positive and negative ion beams. These are duoplasmatron type, Colutron type, and ordinary electron impact type ion sources. We have succeeded in obtaining as high an intensity of positive ion beam, such as of N_2+, as that close to the space-charge limit, i.e., <approximately equal> 10_5 cm^<-3>, after mass selection and deceleration down to a few eV.In addition, we developed a cooled version of the duoplasmatron type ion source to produce cluster ions, with which we studied the photodissociation and collisional dissociation of the cluster ions. Photodissociation of cluster ions (N_2) _2^+, (N_2) _3^+, (CO_2) _2_+, and (N_2O) _2^+has been stuided using a copper vapor laser. It has been found that the only product obtained in the photodissociation of, for example, (CO_2) _2^+is CO_2_+, indicating that the excited states of the dimer ion probed here cannot be an intermediate state of the reaction CO_2^++CO_2*CO_3^++CO. Less