Low-temperature Matrix Isolation Infrared Spectra Of Small Molecular Ions And Free Radicals And Reaction

Simple molecular ions and free radicals are very important reaction intermediates in many chemical processes. The spectra, structure, bonding, and reactivates of transient reaction intermediates and free radicals have gained much attention. In this thesis, we report a combined matrix-isolated infrared spectroscopic and theoretical study of some molecular ions including C6H5NO2-, CH2Cl+, CS3; and the reaction between the CH2Cl radical and O2 is also reported. These ions and radicals are prepared by high frequency discharging. The main results are as follows:1. The nitrobenzene anion has been produced by co-deposition of the nitrobenzene neutral with high-frequency discharged Ar at 4 K. The vibrational spectrums of the nitrobenzene anion trapped in solid argon are reported and are assigned on the basis of isotopic shifts and theoretical frequency calculations. Theoretical calculations predicted that the nitrobenzene anion has a planar C2v structure, with a shorter C-N bond and longer N-O bonds with respect to those of nitrobenzene neutral.2. Co-condensation of CH2X2 (X=Cl, Br)/Ar with high frequency discharged argon produced the CH2X2+ cations as the major products. Under visible light irradiation, the CH2X2+ cations dissociated to give the halomethyl cations CH2X+. Vibrational fundamentals of the CH2X+ and CD2X+ cations were assigned. DFT calculations predicted the halomethyl cations to have a planar C2v symmetry with a shorter C-X bond and longer C-H bonds relative to those of the halomethyl free radicals.3. Co-condensation of CS2/Ar with high frequency discharged argon produced carbon monosulfide as well as sulfur atoms. Sample annealing allows the fragments to diffuse and react to form the carbon trisulfide molecule. The C=S stretching and bending vibrations of CS3 are located at 1263.3 and 570.1 cm-1, respectively. The carbon trisulfide molecule was characterized to have a singlet ground state with a C2v symmetry based on isotopic experiments and theoretical calculations. Under visible light irradiation, the CS3 molecule dissociated to form the SCS-S weakly bound complex.4. The reaction of chloromethyl radical with molecular oxygen has been studied. The chloromethyl radicals were produced through co-deposition of chloromethane with high frequency discharged argon atoms. It was found that the chloromethyl radical reacted with dioxygen to form the chloromethylperoxy radical spontaneously on annealing. The chloromethylperoxy radical underwent UV photon induced dissociation to give the the weakly bound ClCO-H2O complex.