ESR and optical evidence on formation of a chloride.cntdot..cntdot..cntdot.trichloromethyl (1+) ion pair in 3-methylpentane matrixes .gamma.-irradiated at 77 K

Abstract

The well-known absorption band at 470 nm in CCl4-alkane systems is investigated. The results obtained are as follows;(1) The absorption band due to the radical cation of 5-methyldecane (5MD+) in 5MD-CC14-3MP systems converts into the 470-nm band. (2) In the conversion, the positive charge of the 5MD+ reacts with the unpaired electron of the CC13* radical. (3) CBrCl3 and CC13F in 3MP glasses produce the absorption bands at 480 and 438 nm, respectively, and the nature of these bands is the same with that of the 470-nm band in the all points examined. Results 1 and 2 lead to the formation of CC13+ cations. We also obtain evidence on the formation of CC13+ cations from CBrCl3 and CC12F+ cations from CC13F. It is evident that the band shift observed in the case of CBrCl3 is not attributable to the free ions CC13+ nor to the solvent-separated ion pairs Br~|solvent|CCl3+ but to the formation of charge-transfer contact ion pairs Br"-CCl3+. Therefore, it is concluded that CC14 and CC13F in 3MP produce Cr-CCl3+ and Cr-CC12F+, respectively. We also obtain the results that CBrF3, CC1F3, and CC12F2 in 3MP glasses yield the corresponding radical anions with absorption bands at 314, 300, and 314 nm, respectively, and that these radical anions are neutralized with the migrating positive charges of the 5MD+ formed.

Mechanisms of Radiation-Induced Degradation of CFCl3 and CF2Cl2 in Noble-Gas Matrixes: An Evidence for “Hot” Ionic Channels in the Solid Phase

“…Indeed, the gas-phase photoionization studies reveal that the energy threshold for formation of such ion pair from the Rydberg excited states of CF 2 Cl 2 lies at 10.6 eV, that is, well below the IE of the parent molecule. Furthermore, it is worth noting that the electronic absorptions in the visible range observed in some γ-irradiated solid freons at 77 K were assigned to trapped ion pairs of this kind. , This is consistent with the photosensitivity of the species observed in our experiment. If this assignment is correct, the appearance of multiple bands in Ar, Kr, and Xe matrixes may be explained provisionally by the matrix site splitting.…”

“…Furthermore, it is worth noting that the electronic absorptions in the visible range observed in some γ-irradiated solid freons at 77 K were assigned to trapped ion pairs of this kind. 42,43 This is consistent with the photosensitivity of the species observed in our experiment. If this assignment is correct, the appearance of multiple bands in Ar, Kr, and Xe matrixes may be explained provisionally by the matrix site splitting.…”

Photoinduced Electron Transfer between Carotenoids and Solvent Molecules

“…Of the solvents used in this paper, CCl 4 is the most extensively studied and documented. Optical and EPR techniques indicated formation of the primary CCl 4 •- radical anions under radiolysis of neat CCl 4 , and hydrocarbon matrices containing CCl 4 . ,− At room temperature, CCl 4 •- dissociates on the subnanosecond time scale to give the CCl 3 • radical and the chloride ion Cl - . − γ-Radiolysis of CCl 4 in TMS matrices at 4 or 77 K produced a predissociation molecular structure (CCl 3 ···Cl) •- with C 3 v symmetry, which converted to CCl 3 • radical upon warming to 150 K . In our previous CIDEP studies, upon photolysis of a carotenoid solution in CCl 4 at room temperature a resolved EPR spectrum due to CCl 3 • formation was not observed.…”

ESR and optical studies of solute n-alkane cations formed in .gamma.-irradiated n-pentane and n-hexane matrixes

“…The mechanism forming Cl2" has been explained as hole trapping by Cl" followed by molecular-ion formation with nearby be noted that the proposed reaction schemes seem closely correlated to the formation of "ion pair" CC13+-C1" in alkane glasses containing CC14 as electron scavenger.29 The reason for this is derived from our combined optical studies with ESR studies that 5-methyldecane (5-MD) cations formed in 77 K 7-irradiated 0.6% 5-MD-l% CCl4-3-MP react selectively with CC13' radicals to form the "ion pair" CC13+-C1". 30 Here, we wish to propose schemes 3 and 4 with the hope that the reaction process can clear up the question why «-C8+ in l-ClC5-«-C6 and also 5-MD+ in CCl4-3-MP react selectively with RCH2* and CC13', respectively. Nevertheless, it should also be noted that decrease of the RCH2' radicals can be explained by the following schemes: H abstraction by Cl', RCH2* + Cl' -» R'CH=CH2 + HC1, and recombination with Cl', RCH2' + Cl' -RCHjCl.…”