Photodissociation partial

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. 

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... 

Fig. 30. Contour plot of photoelectron-photodissociation coincidence spectrum as a distribution of photoelectron intensity (dark shade = low, light shade = high) against the electron binding energy and relative translational energy of the photofragments. Also shown on the left and at the bottom are the partially averaged distributions for the translational energy release and the electron binding energy, respectively.

The partial cross section gives the probability of absorbing light and producing a particular final product quantum state. The total photodissociation cross section is clearly given by the sum over all partial photodissociation cross sections ... 

The temporal resolution of both methods is limited by the risetime of the IR detectors and preamplifiers, rather than the delay generators (for CS work) or transient recorders (SS) used to acquire the data, and is typically a few hundred nanoseconds. For experiments at low total pressure the time between gas-kinetic collisions is considerably longer, for example, approximately 8 /is for self-collisions of HF at lOmTorr. Nascent rotational and vibrational distributions of excited fragments following photodissociation can thus be obtained from spectra taken at several microseconds delay, subject to adequate SNR at the low pressures used. For products of chemical reactions, the risetime of the IR emission will depend upon the rate constant, and even for a reaction that proceeds at the gas-kinetic rate the intensity may not reach its maximum for tens of microseconds. Although the products may only have suffered one or two collisions, and the vibrational distribution is still the initial one, rotational distributions may be partially relaxed. 

As might be expected this cluster shows interesting photochemical properties that seem to arise from partial photodissociation of the unique Cu(III) ion followed by a two-electron transfer from reducing substrates. Work in progress is aimed at understanding the interesting photochemistry of this cluster. 

A great deal of work has been done on the photodissociation dynamics of the halogen containing compounds. This is partially due to the production of halogen atoms and radicals that can be studied by TOF and partially due to the fact there are intense absorption bands in the ultraviolet and near ultraviolet region. These reasons, coupled with the fact that the spectroscopy of some precursor molecules is fairly well understood, have resulted in many workers looking at these compounds. Finally, some of these compounds have been studied as possible candidates for various types of lasers. 

From this starting point, the authors develop equations leading to the evaluation of the real symmetric K matrix to specify the scattering process on the repulsive surface and propose its determination by a variational method. Furthermore, they show explicitly the conditions under which their rigorous equations reduce to the half-collision approximation. A noteworthy result of their approach which results because of the exact treatment of interchannel coupling is that only on-the-energy-shell contributions appear in the partial linewidth. Half-collision partial linewidths are found not to be exact unless off-the-shell contributions are accidentally zero or (equivalently) unless the interchannel coupling is zero. The extension of the approach to indirect photodissociation has also been presented. The method has been applied to direct dissociation of HCN, DCN, and TCN and to predissociation of HCN and DCN (21b). 

Partially deuteriated vinyl chloride has been used693 to elucidate its UV photodissociation dynamics. The hydrogen abstraction process by chlorine atom has been found to be the RDS in the reaction of normal and deuteriated alcohols with chlorine atoms generated by pulse radiolysis in CCI4 at 18 °c694. 

In the following we will call the a u,n,j) partial photodissociation cross sections.t They are the cross sections for absorbing a photon with frequency u and producing the diatomic fragment in a particular vibrational-rotational state (n,j). Partial dissociation cross sections for several photolysis frequencies constitute the main body of experimental data and the comparison with theoretical results is based mainly on them. Summation over all product channels (n,j) yields the total photodissociation cross section or absorption cross section ... 

Let us assume that the upper state is degenerate with substates F, all corresponding to the same total energy Ef. The photon excites each of these states simultaneously because the resonance condition ujfi ui holds for all of them. The absorption cross section is consequently composed of several partial absorption cross sections cr(u), [3) each being defined as in (2.27) with Ff) replaced by F ). We will come back to this in Section 2.5 when discussing photodissociation. 

Coupling to other vibrational channels is zero and transitions from one vibrational state to another are therefore prohibited. Within the adiabatic approximation the partial photodissociation wavefunctions separate into a translational and an internal part, the latter depending parametrically on R, i.e.,... 

Inserting (3.38) into the expression for the partial photodissociation amplitudes yields... 

With the excited-state wavefunction given by (3.38) the partial photodissociation cross sections approximately reduce to... 

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