Iodine atoms, excited, from

Fig. 3.—Fraction of vi, the energy available after iodine atom excitation, which appears in internal excitation of the alkyl fragment, plotted against identity of the parent molecule (arbitrary scale). The points are A, statistical model, eqn (12), a = 0 V, statistical model, eqn (12), a = 1 O, soft radical impulsive model, eqn (13) , experimental , rigid radical impulsive model, eqn (14). The experimental points are derived from the major peaks in fig. 2, assumed to represent I production for CH3I, C2H5I and n-CjH . For iso-CjH the peak may be a mixture of I and I, and the experimental point is the energy disposal averaged between the values for I and I production. The curves linking the points are intended only as a visual guide.

Unlike the situation regarding the crossing between the Vq and Fj potentials for Nal (see Figure 9.41), that for NaBr results in very efficient and rapid dissociation to give Na + Br when it is excited to Fj. Flow would you expect the fluorescence intensity from the neutral bromine atoms to vary with time compared with that for iodine atoms from Nal in Figure 9.42 ... 

A dilute I2/CCI4 solution was pumped by a 520 nm visible laser pulse, promoting the iodine molecule from its ground electronic state X to the excited states A,A, B, and ti (Fig. 4). The laser-excited I2 dissociates rapidly into an unstable intermediate (I2). The latter decomposes, and the two iodine atoms recombine either geminately (a) or nongeminately (b) ... 

It is unlikely that the compound (27) is derived directly from the reaction of an excited benzene with tetrafluorobenzyne even though the compound (27) is formally analogous to the photo-adducts formed by the irradiation of olefins in benzene 74,75) A number of other products derived from the o-iodotetrafluorophenyl radical were also obtained 73>. These results suggest either that the tetrafluoro-o-phenylene di-radical (32) is identical with tetrafluorobenzyne or that if it is produced at a higher energy level it returns rapidly to the groundstate before it reacts with benzene. An alternative and perhaps more likely explanation is that the tetrafluorobenzyne formed arises by the concerted loss of both iodine atoms. 

Early work by Rollefson and Booher1 in 1931 and by Goodeve and Taylor2 in 1936 established that gaseons hydrogen iodide displays an absorption continuum from 2000 to 4000 A with a maximum at about 2200 A. It was recognised that at wavelengths below 3100 A excited iodine atoms would be produced and that... 

The proportions of ground-state and (2P ) excited iodine atoms produced in a photolysis using monochromatic radiation can be approximately calculated from Fig. 1. To conserve momentum, essentially all the energy from the primary process in excess of that used in bond dissociation (HI -> H+I) =... 

In suggesting an increased effort on the experimental study of reaction rates, it is to be hoped that the systems studied will be those whose properties are rather better defined than many have been. By far and away more information is known about the rate of reactions of the solvated electron in various solvents from hydrocarbons to water. Yet of all reactants, few can be so poorly understood. The radius and solvent structure are certainly not well known, and even its energetics are imprecisely known. The mobility and importance of long-range electron transfer are not always well characterised, either. Iodine atom recombination is probably the next most frequently studied reaction. Not only are the excited states and electronic relaxation processes of iodine molecules complex [266, 293], but also the vibrational relaxation rate of vibrationally excited recombined iodine molecules may be at least as slow as the recombination rate [57], Again, the iodine atom recombination process is hardly ideal. 

We present a preliminary study on the structural dynamics of photo-excited iodine in methanol. At early time delays after dissociation, 1 - 10 ns, the change in the diffracted intensity AS(q, t) is oscillatory and the high-q part 4 -8 A 1 is assigned to free iodine atoms. At later times, 10-100 ns, expansive motion is seen in the bulk liquid. The expansion is driven by energy released from the recombination of iodine atoms. The AS(q, t) curves between 0.1 and 5 (is coincide with the temperature differential dS/dT for static methanol with a temperature rise of 2.5 K. However, this temperature is five times greater than the temperature deduced from the energy of dissociated atoms at 1 ns. The discrepancy is ascribed to a short-lived state that recombines on the sub-nanosecond time scale. 

Znl (g). Sponer4 estimated Dz= —46, from spectroscopic data, for the dissociation into gaseous normal zinc and iodine atoms. Wieland1 reported a value for the energy of the excited state of gaseous Znl. 

Agl (g). Jellinek and Rudat2 computed the heat of vaporization from vapor pressure data. From the spectroscopic absorption limit and the assumption that the products of dissociation are a normal silver atom and an excited iodine atom, Franck and Kuhn1 computed a value for the energy of dissociation of gaseous silver iodide which leads to the value Qf= —38 for Agl (g). 

From the spectroscopic side it may be concluded that the same interpretation of the continuous spectrum exhibited by hydrogen-iodide may be adopted as was proposed for non-polar molecules that gaseous hydrogen-iodide dissociates in a single and elementary act after absorption of radiation into a normal hydrogen atom and an excited iodine atom. 

Equation (7.89) also shows that Dq may be obtained from vlimit since Avatomic is the wavenumber difference between two atomic states, the ground state 2P3/2 and the first excited state 2 P /2 of the iodine atom, known accurately from the atomic spectrum. Thus the accuracy of D, j is limited only by that of vlimit. 

In both cases, the branching ratio for electronically excited products was low ( 0.015 and 0.001, respectively). Thus, the two distinct mechanisms mentioned above producing HC1 from H + IC1 do not correlate with the formation of the iodine atom in either the ground state or the excited state as the branching ratio for the two pathways is measured as 0.23. 

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