Knowledge Bank

A spectrometer is described for detecting visible and near-UV fluoresence following photo-ionization. Wavelength resolution is of the order of 2nm, and there are capabilities for observing wavelength-resolved fluorescence decay times in coincidence with mass-analyzed ions, and for determining wavelength-resolved fluorescence lifetimes by an ion-drift method. Photo-ionization of pentafluorocyanobenzene yields a parent-ion fluorescence spectrum reminiscent of polyfluorobenzene ion spectra, while other nitriles yield either no fluorescence, or CN neutral emission through a nonionizing process. Wavelength resolved fluorescence lifetime spectra of $CO2+$ and $CS2\mathrm{<mrow\; data-mjx-texclass="ORD">+</mrow>}A\to X$ emissions were obtained. $CO2\mathrm{<mrow\; data-mjx-texclass="ORD">+</mrow>}$ shows no wavelength dependence of the fluorescence lifetimes; the $CS2\mathrm{<mrow\; data-mjx-texclass="ORD">+</mrow>}$ spectrum, while perhaps non-uniform, does not show wavelength variation which can be readily attributed to different excited state lifetimes. It is concluded that neither of these ions has dramatic variation in excited state lifetimes, although the data precision for $CS2\mathrm{<mrow\; data-mjx-texclass="ORD">+</mrow>}$ still modest. An average lifetime of $CO2\mathrm{<mrow\; data-mjx-texclass="ORD">+</mrow>}A~2\pi u$ of 123 nsec was found, and an average of 3.8 $\mu$sec for $CS2\mathrm{<mrow\; data-mjx-texclass="ORD">+</mrow>}A~2\pi u$.