Photochemistry in Molecular Beams

In a photochemical experiment the molecular beam crosses a laser beam which can be pulsed or continuous, and the photoproducts are analysed in a 

The path of the laser beam and the detector (the ionizer in this case) define a plane perpendicular to the scattering plane in which the source of the molecular beam can be rotated to some scattering angle a. Neutral photofragments are detected through ionization by electron impact. Ions formed in this way can be mass selected in electric and/or magnetic fields. 

When a pulsed molecular beam is used with a pulsed laser beam, the velocity of the photofragments can be obtained from the delay time between 

Molecular beam techniques have been used mostly with small molecules, and most of the information about the dynamics of elementary photochemical processes are restricted to such species. It is however also possible to bring relatively large molecules (e.g. aromatics) into molecular beams through seeding in a carrier gas such as He. 

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In the first place, we shall take a look at the recent advances in fast reaction photochemical kinetics and spectroscopy, in particular at picosecond laser flash photolysis and femtosecond observations. Next, photophysics and photochemistry in molecular beams will be considered. Here observations are made under single molecule-single photon conditions, and these experiments provide insight into the most fundamental unimolecular gas phase reactions. 

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