| Description |
This dissertation focuses initially on development of a nanoparticle mass spectrometer (NPMS) for single particle analysis utilizing a split ring electrode trap (SRET). Electrospray ionization generates nanoparticle ions that are guided and trapped in the SRET. Detection of single particles occurs by observing light scattered or fluorescence emitted from the particle. Three methods are used to determine the secular frequency (®z) of a single trapped particle: Fourier transform analysis of scattered light intensity, frequency sweep of the laser force, or frequency sweep of a constant AC voltage. From ©z, the mass-to-charge ratio may be ascertained. The AC frequency sweep method results in a peak width nearing 10 ppm. By averaging the peak position of multiple AC frequency sweep measurements, precision approaches 1 ppm. This method is then applied to single core-shell CdSe/ZnS quantum dots by activating their fluorescence with a CO2 laser. The secular frequency, mass, charge, and fluorescence intensity are tracked for a single QD over multiple days. Heating the QD sublimates the particle and causes it to eventually go dark. Once dark, the QD remains in the trap and begins to fluoresce intermittently. The focus of the later half is on reactions of vibrationally state-selected HOD+. Each of the fundamental vibrational states of HOD+ was investigated. Cross sections and product velocity distributions were obtained for every product for each reaction and each vibrational state investigated. Reactions of HOD+ with CO, N2O, CO2, and N2 were investigated. These reactions were chosen because proton transfer is endoergic for each reaction or thermoneutral. Mode- and bond-selective enhancement was observed for the cross sections of H+ and D+ transfer for the OH and OD stretch, respectively. The bend vibration also enhances reactivity; in some cases, the total enhancement for the bend is greater than that of the OH or OD stretches. Velocity distributions indicated that the mechanism for H+ and D+ transfer near threshold might be complex mediated, but it is difficult to tell because there is little energy available to the system near threshold. However, with increasing collision energy (Ecol), the reaction becomes increasingly direct and backward scattered. |
