Visible laser studies photodissociation

We use laser photofragment spectroscopy to study the vibrational and electronic spectroscopy of ions. Our photofragment spectrometer is shown schematically in Eig. 2. Ions are formed by laser ablation of a metal rod, followed by ion molecule reactions, cool in a supersonic expansion and are accelerated into a dual TOE mass spectrometer. When they reach the reflectron, the mass-selected ions of interest are irradiated using one or more lasers operating in the infrared (IR), visible, or UV. Ions that absorb light can photodissociate, producing fragment ions that are mass analyzed and detected. Each of these steps will be discussed in more detail below, with particular emphasis on the ions of interest. 

Photodissociation dynamics [89,90] is one of the most active fields of current research into chemical physics. As well as the scalar attributes of product state distributions, vector correlations between the dissociating parent molecule and its photofragments are now being explored [91-93]. The majority of studies have used one or more visible or ultraviolet photons to excite the molecule to a dissociative electronically excited state, and following dissociation the vibrational, rotational, translational, and fine-structure distributions of the fragments have been measured using a variety of pump-probe laser-based detection techniques (for recent examples see references 94-100). Vibrationally mediated photodissociation, in which one photon... 

This molecule is ideal for photodissociation dynamics studies, since it has allowed excited states in the visible region of the spectrum which is more easily accessible with tunable lasers. Both products can in principle be detected using the LIF method, though at the present time only the product distribution of the CN radical has been measured, since NO is often present as an impurity. The spectroscopy is also well studied... 

The editor has encountered numerous studies of laser ignition, usually of explosives. These demonstrate that the ignition is normally a thermal effect, caused by heating solid particles, not photochemical, and thus the MIE is not lower than other methods. This may not obtain if the light be of a frequency (visible or uv) sufficient to excite the early steps of the explosion reaction, as, for example, photodissociation of halogens to the atomic radicals which are the start of their explosive reactions with fuels. 

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