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Gamma-irradiated polycrystalline CCl4 at 77°K provides evidence that positive charge migrates and is trapped by the matrix itself. The trapped positive hole absorbs at about λmax=400 mμ in pure CCl4 or dilute solid solutions of aromatic amines. The solvent band is depressed by aromatic amines or other additives which act as hole traps with appearance of the corresponding amine cation absorption. After γ irradiation the residual 400-mμ band photobleaches at 77°K with increase in solute cation absorption. Brief heating to 143°K gives the same result. A kinetic treatment which assumes that the only labile species in the system is migrating positive charge can explain the experimental results in a satisfactory way. The kinetic analysis gives a rough estimate of total available positive charge created per 100 eV of absorbed energy as 1.9. Several aromatic amines have been used as test substances and their optical absorption spectra recorded.

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Articles you may be interested inOn the vibronic structure of the absorption spectra of radical cations of some polycyclic aromatic hydrocarbons

Photoionization cross sections in resonance ionization mass spectrometry of sputtered metal atoms: Applications to material analysis Proton transfer is the most probable type of reaction observed in a number of ion-molecule interactions involving permanent dipoles. Integrated cross sections, which are unusually large, are described in terms of an ion-dipole pair oriented near the position of minimum energy at low relative velocity. As the relative velocity is increased, this alignment becomes less likely. The energy-dependent cross section is eclipsed at high relative velocity by the "hard" cross section which does not vary with energy. Proton affinities are estimated for several alkyl cyanides. Some of the reported reactions appear to involve excited states of the primary ions.

An improved method of measuring ionization efficiency (I.E.) curves by the retarding potential difference technique in the mass spectrometer (to ∼one ion/sec at onset) gives ionization potentials which agree within ± 0.02 eV of spectroscopic values and ± 0.03 eV of photoionization. Ionization potentials I have been measured for the following free radicals (eV): CH3, 9.87; C2H5, 8.34; n-C3H7, 8.13; i-C3H7, 7.57; n-C4H9, 8.01; C2H5O, 9.11; n-C3H7O, 9.20; i-C3H7O, 9.20; n-C4H9O, 9.22. Appearance potentials V have been measured for R+/RX, where R=CH3, C2H5, n-C3H7, n-C4H9 and X=H, Cl, Br, I, and OR; also for RO+/ROX where R=C2H5, i-C3H7, n-C4H9 and X=H, NO, and R; also for I+/n-C4H9I, NO+/C2H5ONO, NO+/n-C4H9ONO, and C3H6D+/CH3CD2CH3. Values of ΔHf(R+), ΔHf(RO+), D(R−X), and D(RO−X) are reported as well as electron affinities of NO, C2H5O, n-C3H7O, i-C3H7O, and n-C4H9O. Whenever two or more independent measurements of V provide the same ΔHf or D, agreement is satisfactory. The linearity of onsets does not correlate with photoionization efficiency curves according to present threshold theory. The “breaks” in I.E. curves do yield thermochemically consistent results.

The energy dependence of reaction cross sections has been observed for various ion-molecule reactions. The secondary ions C4HI0Br2+, C4HsBr+, CIHloRr+, CpHaBr2-and CHRr2' from C2H5Br; CsH1412+ from n-CaH71 and C6HI4C1+ from s-C3117C1 indicate low energy limits of stability. Tropylium and substituted tropylium ions appear to result from reactions of CHI+, CD3+, CHC12T and CC13* with C&; they give evidence of transitions in reaction cross sections a t cn. 1.3-2.0 ev. inn energy which are identified with instability resulting from head-on collisions.

)) where iq[R] is the frequency of electron transfer and ¡/2[S] is the frequency of dry hole localization, e.g., by formation of H30+. For 1 -~1, the direct and indirect yields are algebraically indistinguishable.Large yields of SO4-in D2O cannot be explained by . They are attributed to the vibration-limited frequency V2 which increases the lifetime of D20+.