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Delayed fragmentation of acetonitrile upon short‐pulse UV irradiation: Possible role of long‐lived superexcited intermediates
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2.A preliminary report on this work has been given: B. B. Craig, W. L. Faust, and R. G. Weiss, in Lasers as Reac‐tants and Probes in Chemistry, edited by W. M. Jackson and A. B. Harvey (Howard University, Washington, D.C., in press).
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15.Available through the Physics Auxiliary Publication Service of the AIP: the isotopic abundance of the parent acetonitriles employed, and computed coefficients of emission intensities in various channels of fragmentation.
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18.In principle, such a determination might be achieved by a study of yield vs fluence. We believe, however, that in this experiment excitation passes through both nonresonant and resonant states; consequently, the saturation parameters of successive steps vary widely. The fluence must be sufficiently large that the weak nonresonant steps may proceed at adequate rates to support observation of the overall processes. The strong resonant steps will then be driven far into saturation, and the quantum order will be underestimated. For acetonitrile the problem is exacerbated by the onset of essentially different processes (see CN A state, below).
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24.In a trivial sense, an emission waveform necessarily reflects the time history of the emissive population. However, the rate parameters which define the shape of the waveform do not necessarily belong to the emissive species; see, for example, the kinetic processes described in B. B. Craig, W. L. Faust, L. S. Goldberg, and R. G. Weiss, Chem. Phys. Lett. 83, 265 (1981).
25.Throughout this paper, the cited error limits represent estimates for one standard deviation.
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46.McElcheran et al. do not consider elimination to be possible at 184.9 nm (see Ref. 3). It is interesting that has not been reported for higher energies. In photolysis of ethane, the major yield of hydrogen species has been found to occur through elimination of from a single methyl group; see H. Okabe and J. R. McNesby, J. Chem. Phys. 34, 668 (1961).
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49.In this connection, we note that the rise of Balmer emission is not instrumentally limited.
50.We note that H elimination generates the cyanomethyl radical. In its ground state this species includes a resonance contribution from the allenic form this could represent a first step in redistribution of the π‐electron system leading toward intramolecular Theoretical calculations suggest that his radical possesses stable cyclic as well as linear forms; further, it may undergo skeletal isomerization and H migration: Z. Slanina and Z. R. Grabowski, Collect. Czech. Chem. Commun. 44, 3441 (1979);
50.see Fig. 1 therein.
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56.This assumes thermal collision velocities. Even if there is H elimination in the channel(s) leading to the precursors, the dissociation velocity of fragments such as will be quite small.
57.Similar considerations were advanced in Ref. 55 and in G. A. West and M. J. Berry, Chem. Phys. Lett. 56, 423 (1978).
58.This is the case for radiative transitions: D. R. Bates and A. Damgaard, Philos. Trans. R. Soc. London Ser. A 242, 101 (1950).
59.For example, similarly large quenching rates have been observed for states which do not include Rydberg orbitals: J. B. Halpern, G. Hancock, M. Lenzi, and K. H. Welge, J. Chem. Phys. 63, 4808 (1975);
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