Strong-field ionization of flash pyrolysis reaction products.

We report the coupling of a flash pyrolysis molecular beam source with nonresonant strong-field ionization in a time-of-flight mass spectrometer. The saturation laser intensities at which ionization occurs for the various product species are generally found to correlate closely with the ionization energies, as has been seen for closed-shell molecules. It is then possible to use this correlation to identify the product and quantify isomers from among several candidate species whose ionization energies are known. The approach is analogous to using tunable vacuum ultraviolet ionization to identify reaction products.

Coincidence ion imaging with a fast frame camera.

A new time- and position-sensitive particle detection system based on a fast frame CMOS (complementary metal-oxide semiconductors) camera is developed for coincidence ion imaging. The system is composed of four major components: a conventional microchannel plate/phosphor screen ion imager, a fast frame CMOS camera, a single anode photomultiplier tube (PMT), and a high-speed digitizer. The system collects the positional information of ions from a fast frame camera through real-time centroiding while the arrival times are obtained from the timing signal of a PMT processed by a high-speed digitizer. Multi-hit capability is achieved by correlating the intensity of ion spots on each camera frame with the peak heights on the corresponding time-of-flight spectrum of a PMT. Efficient computer algorithms are developed to process camera frames and digitizer traces in real-time at 1 kHz laser repetition rate. We demonstrate the capability of this system by detecting a momentum-matched co-fragments pair (methyl and iodine cations) produced from strong field dissociative double ionization of methyl iodide.

Isomer-specific mass spectrometric detection via "semisoft" strong-field ionization.

Time-of-flight mass spectra obtained for strong-field ionization using simply a transform-limited femtosecond laser pulse allows for quantitative characterization of the composition of an unknown mixture, including determination of isomeric composition. The approach is described and example applications presented.