The photodissociation of

The temi action spectroscopy refers to how a particular action , or process, depends on photon energy. For example, the photodissociation of 0 with UV light leads to energetic 0+0 fragments the kinetic energy released has been... 

Schwarzer D, Schroeder J and Schroder Ch 2000 Quantum yields for the photodissociation of iodine in compressed liquids and supercritical fluids Z. Phys. Chem. 214... 

Murrell J N, Stace A J and Dammel R 1978 Computer simulation of the cage effect in the photodissociation of iodine J. Chem. Soc. Faraday Trans. II 74 1532... 

Dardi P S and Dahler J S 1993 A model for nonadiabatic coupling in the photodissociation of l2-solvent complexes J. Chem. Phys. 98 363-72... 

Gezelter J D and Miller W H 1996 Dynamics of the photodissociation of triplet ketene J. Chem. Phys. 104 3546-54... 

The experiments were perfonued in a static reaction cell in a large excess of N2 (2-200 bar). An UV laser pulse (193 mu, 20 ns) started the reaction by the photodissociation of N2O to fonu O atoms in the presence of NO. The reaction was monitored via the NO2 absorption at 405 mu using a Hg-Xe high-pressure arc lamp, together with direct time-dependent detection. With a 20-200-fold excess of NO, the fonuation of NO2 followed a pseudo-first-order rate law ... 

Figure B2.5.10. LIF signal of free Na atoms produced in the photodissociation of Nal. t - q is the delay between the photolysis pulse (at L) and the probe pulse. Adapted from [111].

Schinke R, Weide K, Heumann B and Engel V 1991 Diffuse structures and periodic orbits in the photodissociation of small polyatomic molecules Faraday Discuss. Chem. Soc. 91 31... 

Figure 3, Wavepacket dynamics of the photodissociation of NOCl, shown as snapshots of the density (wavepacket amplitude squared) at various times, The coordinates, in au, are described in Figure b, and the wavepacket is initially the ground-state vibronic wave function vertically excited onto the 5i state. Increasing corresponds to chlorine dissociation. The density has been integrated over the angular coordinate. The 5i PES is ploted for the geometry, 9 = 127, the ground-state equilibrium value,...

Irradiation of the molecular radical anion of DESO, which has a yellow color, with light of X = 350-400 nm partially restores the red color and the ESR spectrum of the radical-anion pair. Similarly to the case of DMSO-d6 a comparison of the energetics of the photodissociation of the radical anion and dissociative capture of an electron by a DESO molecule permits an estimation of the energy of the hot electrons which form the radical-anion pair of DESO. This energy is equal to 2eV, similarly to DMSO-d6. The spin density on the ethyl radical in the radical-anion pair of DESO can be estimated from the decrease in hfs in comparison with the free radical to be 0.81, smaller than DMSO-d6. 

Uncertainties in Photochemical Models. The ability of photochemical models to accurately predict HO concentrations is undoubtedly more reliable in clean vs. polluted air, since the number of processes that affect [HO ] and [H02 ] is much greater in the presence of NMHC. Logan et al (58) have obtained simplified equations for [HO ] and [HO2 ] for conditions where NMHC chemistry can be ignored. The equation for HO concentration is given in Equation E6. The first term in the numerator refers to the fraction of excited oxygen atoms formed in R1 that react to form HO J refers to the photodissociation of hydrogen peroxide to form 2 HO molecules other rate constants refer to numbered reactions above. 

Here, X may be H, OH, NO, Cl, or Br. Cl from the photodissociation of chlorofluoro-carbons such as CFC-12 (CCI2F2) is the main known catalyst currently acting in the so-called... 

Multiple pathways leading to the same product channel can also be observed in a reaction when there are a sufficient number of identical atoms, thereby allowing different intermediate structures to yield the same products. In these cases, the mechanisms in the two pathways are often quite similar, but involve differing positions of identical atoms on the reactants. The different pathways often involve formation of ring intermediates in which the rings have different sizes. A simple example of this class is the photodissociation of vinyl chloride [9]... 

Reactions without wells can also exhibit multiple pathways due to deviation from the MEP. While many trajectories may follow the MEP over a saddle point, alternative pathways arise when forces on the PES steer away from the saddle point, typically into relatively flat regions of the PES, before finding an additional path to the same exit channel. The roaming mechanisms recently elucidated in the photodissociation of formaldehyde and acetaldehyde, and the reaction of CH3 + O, are examples of this phenomenon, and are discussed in Section V. 

The degree of vibrational excitation in a newly formed bond (or vibrational mode) of the products may also increase with increasing difference in bond length (or normal coordinate displacement) between the transition state and the separated products. For example, in the photodissociation of vinyl chloride [9] (reaction 7), the H—Cl bond length at the transition state for four-center elimination is 1.80 A, whereas in the three-center elimination, it is 1.40 A. A Franck-Condon projection of these bond lengths onto that of an HCl molecule at equilibrium (1.275 A) will result in greater product vibrational excitation from the four-center transition state pathway, and provides a metric to distinguish between the two pathways. 

However, as the CH3 + O reaction shows [67], the roaming atom mechanism is not limited to closed-shell adducts, nor is it limited to abstraction pathways that are barrierless (see Fig. 13). Finally, the photodissociation of CH3CHO implies that the roaming fragment may not be limited to H atoms [55]. It remains to be seen how universal roaming mechanisms are, but they have the potential to be competing pathways in a large number of reactions. 

Since H-atom products from chemical reactions normally do not carry any internal energy excitation with its first excited state at 10.2 eV, which is out of reach for most chemical activations, the high-resolution translational energy distribution of the H-atom products directly reflects the quantum state distribution of its partner product. For example, in the photodissociation of H2O in a molecular beam condition,... 

The time-of-flight spectrum of the H-atom product from the H20 photodissociation at 157 nm was measured using the HRTOF technique described above. The experimental TOF spectrum is then converted into the total product translational distribution of the photodissociation products. Figure 5 shows the total product translational energy spectrum of H20 photodissociation at 157.6 nm in the molecular beam condition (with rotational temperature 10 K or less). Five vibrational features have been observed in each of this spectrum, which can be easily assigned to the vibrationally excited OH (v = 0 to 4) products from the photodissociation of H20 at 157.6 nm. In the experiment under the molecular beam condition, rotational structures with larger N quantum numbers are partially resolved. By integrating the whole area of each vibrational manifold, the OH vibrational state distribution from the H2O sample at 10 K can be obtained. In... 

Similarly, the TOF spectrum of the D-atom product from the mixed sample has also been measured. Figure 8(a) shows the translational energy distribution for the D-atom product from the mixed sample. In order to show the contribution from the D20 photodissociation, Fig. 8(b) also shows the translational energy distribution for the photodissociation of the pure D20 sample converted from the D-atom TOF spectrum using a mass ratio... 

MULTIMASS ION IMAGING — A NEW EXPERIMENTAL METHOD AND ITS APPLICATION IN THE PHOTODISSOCIATION OF SMALL AROMATIC MOLECULES... 

In the following sections, we describe the principles of this new experimental technique,9 and show the application of this technique in the photodissociation of small aromatic molecules. 

The photodissociation of isotope labelled toluene C6H5CD3 and C6H513CH3 at 193 nm and 248 nm under collision-free conditions were... 

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