Excitation product translational

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... 

Luminescence spectra resulting from pure vibrational or V-R transitions involving excited-product states formed in ion-neutral collisions have not yet been observed. However, vibrational and rotational excitation of the products of reactive ion-neutral collisions may be determined indirectly from measurements of Q, the translational exoergicity, which is defined as the difference between the translational energy of the products and that of the reactants. According to the energy-conservation principle, then,... 

The majority of the available information on electronically excited products formed in ion-neutral reactions has been derived from luminescence measurements. A comprehensive review of such data for the period up to 1970, which deals with ion interactions at translational energies of 10 eV and higher, is available.258 More recent work is summarized here. 

In chemiluminescence experiments such as those described previously in the experimental section, emission spectra characteristic of the excited products of ion-neutral collisions are obtained, that is, intensities of the emitted radiation as a function of wavelength. This permits identification of the electronically excited states produced in the reaction as well as determination of the relative populations of these states. In addition if the luminescence measurements are made using beam techniques, excitation functions (intensity of a given transition as a function of the translational energy of the reactants) can be measured for certain transitions. As is discussed later, some of the observed transitions exhibit translational-energy thresholds. In the emission spectra from diatomic or polyatomic product molecules, band systems are sometimes observed from which the relative importance of vibrational and rotational excitation accompanying electronic excitation may be assessed. 

The reaction H + 03 shows a very highly inverted product vibrational distribution peaking at the highest accessible level v = 9 for OH from H + 03 and v = 13 for OD from D + 03). Thus, almost all the available energy ( 93%) appears in the newly formed bond leaving only 7% to be partitioned between product translation and internal excitation of the 02 product. There is presently no experimental information regarding this partitioning. 

The reactions of barium with benzylchloride, o-, p- and m-chloro-toluene have been studied under beam-gas conditions with laser-induced fluorescence detection of the BaCl and also the benzyl radical (in the case of Ba + benzyl chloride and o-chlorotoluene). For the four reactions, the amount of BaCl internal excitation was small ( 13 kJmole-1), implying that a substantial amount of the reaction energy must appear as product translation or internal excitation of the radical [374]. 

The reaction of OH with Br2 has been studied under crossed-mol-ecular beam conditions [38] and was found to indicate the existence of a stable HOBrBr complex with a lifetime of several rotational periods. The HOBr product translational energy distribution was found to be well described by the RRKM—AM model and to be similar to the OX distribution from the reactions O + Br2 and I2. This is despite the fact that OH is isoelectronic with a F atom and that the most relevant study shows that Cl + Br2 is a direct stripping reaction. The fraction of the total energy appearing in product translation is 36% and there is some indication that the beam source contains a small proportion of vibrationally excited OH which may account for the measured product translational energy distribution extending beyond the maximum allowed for the reaction OH(z> = 0) + Br2. 

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