Photoionization: A Universal Phenomenon
Photoionization processes occur, quite literally, across the universe — driven by energetic starlight in interstellar gas clouds of the nebulae or in planetary atmospheres (including our own). Molecular ions, however created, are typically highly reactive due to their excitation energy and the attractive electrical charge they carry. This gives their presence in any chemical environment – terrestrial or astronomical – an enhanced significance. From the research lab to the factory to the home, molecular ions feature in chemical analysis techniques, in high-tech plasma processing, and in simple combustion processes.
Photoionization in the Lab
For the research scientist, photoionization offers multiple attractions as a means to create ions in the laboratory. The variability of frequency (wavelength), intensity, and polarization that can be achieved with current light sources such as lasers, synchrotrons – and now free-electron lasers – provides opportunities to exert maximum control over the energy and momentum deposited into the nascent ion.
Photoelectrons
But the photoelectrons emitted upon photoionization are also of interest. They carry with them a signature of the molecular system left behind — before, during, and even after after, the photoionization event takes place. Photoelectron studies therefore provide a way to both probe the mutual interaction of electrons within a molecule and to select or identify the quantum state, stereochemical structure, and even orientation of the photoion so created. Having control of these properties promises unprecedented detail in the study of molecular ion chemistry.
Planetary Ions
chemistry play vital roles in
the atmosphere of Titan (one of Saturn's moons)
and in our own Earth's upper atmosphere.
Astronomical Ions
Photoionization by central starlight creates ions
in planetary nebulae and HH type jet outflows of gas.
