Ionic intermediates produced by gamma irradiation at 4 K: Halogenated naphthalene and benzene derivatives in ethanol

Abstract

Optical absorption and ESR measurements have been performed for the irradiated halogenated benzene and naphthalene derivatives in ethanol at 4 K. The anions of both bromo-and chloronaphthalene derivatives were observed under steady state at 4 K, while the former anion at 77 K results in dissociation and the latter anion results in protonation. Both anions of benzene and fluorobenzene were stable at 4 K, whereas not at 77 K, indicating that protonation is inhibited at 4 K. Irradiated iodobenzene and bromobenzene solutions at 4 K showed a doublet band whose energy separation was 0.8--D.9 and 0.41--D.48 eV, which are close to the energy separation between 2 P J!2 and 2 PI 12 of I and Br, respectively. The transition energies of the long wavelength bands of these compounds and of chlorobenzene is linear with the ionization potentials of respective halide ions with a slope of close to unity. Therefore these bands may be assigned to an electron transfer band from halide ion to its counterpart benzene ring. As the electron acceptor, two models were discussed, one of which is the orbital of neutral benzene, and the other is the orbital of the phenyl radical. In solid phase, dissociative electron attachment to halogenated benzene goes through a state of metastable C T complex of a halide ion and its counterpart molecule. The irradiated p -C 6 H.BrI showed also a well resolved doublet band, suggesting that C-I bond rupture is more dominant than C-Br bond rupture. The absorption spectrum of irradiated p -C 6 H.BrCI in ethanol did not resemble either the irradiated chlorobenzene or bromobenzene derivatives, suggesting that both C-Br and C-CI are ruptured at the same time.990

Charge transfer band of the benzyl radical-halide ion formed by dissociative electron attachment to benzyl halides in a rigid organic matrix

“…As far as the present au-thors know, no CT band has not yet been reported for a complex between the neutral free radical and ion except the band observed by Namiki, who could not, however, identify the structure of the free radical. 23 The observed transition energy of the CT band agrees well with that predicted by the ionization energy and the solvation energy of fluoride, chloride, bromide, and iodide as electron donors. However, the red-shift of the spectra is only partly but not totally rationalized by the simple Coulombic field effect of the halide ion on the molecular orbital levels of the benzyl radical.…”

“…Because of a large energy separation of 0.942 eV between the 2P3/2 and 2Pi/2 states of atomic iodine due to the spin-orbit interaction, the excited CT state of the iodide ion-benzyl radical complex is expected to comprise two levels, so that the CT band is expected to show two peaks as observed for the ionic intermediate formed from iodobenzene in the EtOH matrix irradiated at 4 K. 23 The spin-orbit interaction energy Figure 6. The dependence of the observed transition energy of the CT band upon the calculated sum of the ionization energy of halide ions (the electron affinity of halogen atoms) and their solvation energy in the 3-methylhexane matrix at 77 K. The line indicates the expected slope of unity.…”

“…The interaction between hydrocarbon radicals and halide ions seems to be interesting not only from the radiation chemical point of view (to elucidate basically an electron scavenge reaction in matrices) but also from the viewpoint of molecular spectroscopy. The interaction between radiolytically generated methyl radicals and halide ions was evidenced also by means of the electron spin resonance method.21 •22 Recently the charge tránsfer absorption bands due to phenyl radical-halide ion complexes were found by irradiating the ethanol matrix containing halobenzenes at 4 K. 23 However, experimental results on the interaction between radicals and ions are still limited. In order to obtain further information on this interaction, we extended here our previous spectroscopic study on the radiolysis of benzyl chloride in rigid matrices to other benzyl halides (fluoride, bromide, and iodide).…”

Benzene Radical Ion in Equilibrium with Solvated Electrons

“…Benzene radical anion is known in cryogenic media, [1][2][3][4] at high pressures, 5 or as a cluster anion with water in a supersonic jet. 6 As an ion-pair it has been observed in solution at low temperatures, and even near room temperature.…”

“…Benzene radical anion is known in cryogenic media, − at high pressures, or as a cluster anion with water in a supersonic jet . As an ion-pair it has been observed in solution at low temperatures, and even near room temperature. , Both benzene and toluene anions have been crystallized as K + /crown ether salts and their structures obtained .…”