Dynamics photodissociation

Spectroscopic detection of the photoffagment can usually be done in a manner that is sensitive to its internal state and can therefore determine the state distribution of the product. When the Doppler detuning of the spectroscopic transition can be determined, the angular distribution of products in different states can be extracted. For, say, the diatomic product from the dissociation of a triatomic molecule this can provide a wealth of information. Nor is there excessive redim-dancy. Different vibrational final states and even different rotational states of the same vibrational ladder can have interestingly different angular distributions. 

Photodissociation, the extension of spectroscopy into the continuum, is a source of reactive species such as H, F, or Cl atoms or OH and other radicals that can be used to initiate bimolecular reactions. Photodissociation processes are important not only in the laboratory but also in the atmosphere as well as the regions of 

Indirect photodissociation can be the result of more than one type of delay. First, the energy may not be made directly available for the motion along the reaction coordinate. If there is time for energy scrambling tiien the dissociation will be a la RRKM, as will be discussed further in Sections 111-1.1 A. There is however another type of delay. It is when electronic energy is made available as vibrational energy of a lower-lying electronic state. 

Molecules such as CH3I or ICN, whose photodissociation dynamics in the gas phase is well studied and analyzed, and which, like H2O, can form products in more than one electronic state, are being increasingly studied in solution to explore the solvent effects that we discuss in Chapter 11. 

Energy-rich polyatomic molecules can be photoprepared in a variety of ways. If the barrier to dissociation is not large then even overtone excitation may be 

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Ashkenazi G, Banin U, Bartana A, Ruhman S and Kosloff R 1997 Quantum description of the impulsive photodissociation dynamics of l, in solution Adv. Chem. Phys. 100 229... 

Flowever, in order to deliver on its promise and maximize its impact on the broader field of chemistry, the methodology of reaction dynamics must be extended toward more complex reactions involving polyatomic molecules and radicals for which even the primary products may not be known. There certainly have been examples of this notably the crossed molecular beams work by Lee [59] on the reactions of O atoms with a series of hydrocarbons. In such cases the spectroscopy of the products is often too complicated to investigate using laser-based techniques, but the recent marriage of intense syncluotron radiation light sources with state-of-the-art scattering instruments holds considerable promise for the elucidation of the bimolecular and photodissociation dynamics of these more complex species. 

Sohinke R 1993 Photodissociation Dynamics (Cambridge Cambridge University Press)... 

Schinke R and Huber J R 1993 Photodissociation dynamics of polyatomic molecules. The relationship between potential energy surfaces and the breaking of molecular bonds J. Rhys. Chem. 97 3463... 

Ashfold M N R, Mordaunt D H and WIson S H S 1996 Photodissociation dynamics of hydride molecules H atom photofragment translational spectroscopy Adv. Photochem. 21 217-95... 

R. Schinke, Photodissociation Dynamics (Cambridge University Press, Cambridge, 1993). 

W. M. Kwok and D. L. Phillips, Solvation effects and short-time photodissociation dynamics of CH2I2 in solution from resonance Raman spectroscopy. Chem. Phys. Lett. 235(3-4), 260-267 (1995). 

Vibrationally mediated photodissociation (VMP) can be used to measure the vibrational spectra of small ions, such as V (OCO). Vibrationally mediated photodissociation is a double resonance technique in which a molecule first absorbs an IR photon. Vibrationally excited molecules are then selectively photodissociated following absorption of a second photon in the UV or visible [114—120]. With neutral molecules, VMP experiments are usually used to measure the spectroscopy of regions of the excited-state potential energy surface that are not Franck-Condon accessible from the ground state and to see how different vibrations affect the photodissociation dynamics. In order for VMP to work, there must be some wavelength at which vibrationally excited molecules have an electronic transition and photodissociate, while vibrationally unexcited molecules do not. In practice, this means that the ion has to have a... 

In 1999, the Klemperer group published experimental results from a dispersed fluorescence study of the linear and T-shaped Ar l2(X, v = 0) conformers to obtain information about the X- and B-state potentials of the complex and to gain insight into the photodissociation dynamics in the B electronic state [65]. In carrying out their analysis, they assumed that the linear and T-shaped conformers existed in a thermodynamic equilibrium, with the abundance of the linear conformer being three times that of the T-shaped conformer. In an effort to test the validity of the thermodynamic hypothesis Bastida, et al. [66], performed a... 

P. Andresen and R. Schinke, in Molecular Photodissociation Dynamics, eds. M. N. R. Ashfold and J. E. Baggott (Royal Society of Chemistry, London, 1987), Chap. 3. 

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