“…Specific experiments have not been performed in benzene, but similar results are expected. For fast electrons, the initial yield of benzene triplet state due to neutralization reactions is about 4.2 molecules/100 eV. , Like the singlet excited state, the triplet also forms an excimer by coupling with a ground-state benzene molecule. , Both the triplet and singlet excimers are probably in equilibrium with their respective monomers, and both equilibriums are expected to be predominantly in the excimer state . The triplet excimer state decays with a lifetime of about 162 ns .…”
The mechanisms responsible for the main products in liquid benzene radiolysis (biphenyl, molecular hydrogen,
and phenyl radical) are probed with protons, helium ions, and carbon ions of a few to 30 MeV energy.
Phenyl radical yields have been examined using iodine scavenging techniques. The results are combined
with similar data for γ-rays and suggest that phenyl radicals mainly react with benzene to give a long-lived
adduct, which leads to polymer formation. Iodine can react with this adduct to give enhanced yields of biphenyl.
Biphenyl is the predominant single hydrocarbon product in the radiolysis of neat benzene with a yield of
0.075 molecule/100 eV. Its yield is nearly independent of radiation type and energy suggesting that its formation
in neat benzene is due to a fast ion−molecule process and not due to phenyl radicals. The total yield of 0.7
radicals/100 eV is almost entirely due to phenyl radicals and H atoms. A reexamination of the fluorescence
from the singlet excited state of benzene suggests that this state is the precursor for molecular hydrogen and
acetylene, whereas the triplet excited state decays to phenyl radicals and H atoms. Most of the excited states
formed in the γ-radiolysis of benzene seem to decay to ground without formation of any product.
“…Specific experiments have not been performed in benzene, but similar results are expected. For fast electrons, the initial yield of benzene triplet state due to neutralization reactions is about 4.2 molecules/100 eV. , Like the singlet excited state, the triplet also forms an excimer by coupling with a ground-state benzene molecule. , Both the triplet and singlet excimers are probably in equilibrium with their respective monomers, and both equilibriums are expected to be predominantly in the excimer state . The triplet excimer state decays with a lifetime of about 162 ns .…”
The mechanisms responsible for the main products in liquid benzene radiolysis (biphenyl, molecular hydrogen,
and phenyl radical) are probed with protons, helium ions, and carbon ions of a few to 30 MeV energy.
Phenyl radical yields have been examined using iodine scavenging techniques. The results are combined
with similar data for γ-rays and suggest that phenyl radicals mainly react with benzene to give a long-lived
adduct, which leads to polymer formation. Iodine can react with this adduct to give enhanced yields of biphenyl.
Biphenyl is the predominant single hydrocarbon product in the radiolysis of neat benzene with a yield of
0.075 molecule/100 eV. Its yield is nearly independent of radiation type and energy suggesting that its formation
in neat benzene is due to a fast ion−molecule process and not due to phenyl radicals. The total yield of 0.7
radicals/100 eV is almost entirely due to phenyl radicals and H atoms. A reexamination of the fluorescence
from the singlet excited state of benzene suggests that this state is the precursor for molecular hydrogen and
acetylene, whereas the triplet excited state decays to phenyl radicals and H atoms. Most of the excited states
formed in the γ-radiolysis of benzene seem to decay to ground without formation of any product.
“…The energy per particle can then be used to obtain relative radiation chemical yields. Only relative yields have been presented here; however, absolute yields with the heavy ions can be obtained using the value of 1.5 molecules/100 eV for β-particles. , The relative fluorescence yields for protons, helium ions, lithium ions, and carbon ions are presented in Figure as a function of the track average LET of the particle. 5 Fluorescence yields (photons/100 eV) for protons (▪), helium ions (·), lithium ions (▴), and carbon ions (◆) relative to that for β-particles as a function of the track average LET.…”
Section: Resultsmentioning
confidence: 99%
“…The observed fluorescence lifetime of benzene is about 27 ns with UV radiation , and with fast electrons . The excited singlet state yield is estimated to be about 1.5 molecules/100 eV, , so it should play an important role in the radiolysis of neat benzene. Direct examination of the yield and decay of the excited singlet state in benzene will eventually be of great importance in understanding the radiation chemistry of this compound with heavy ions.…”
Fluorescence emission has been measured in the radiolysis of neat liquid benzene with 1-15 MeV protons, 5-20 MeV helium ions, 5-30 MeV lithium ions, and 10-30 MeV carbon ions using single photon counting techniques. Companion studies were performed with 90 Sr-90 Y -particles with an average energy of about 1.66 MeV. Within 30-50 ns following the passage of the heavy particles the fluorescence intensity decreases rapidly and then levels off to a much slower decay rate which is very nearly the same for -particles and high-energy protons and helium ions. The lifetimes of both the fast and slow components of the fluorescence decrease with increasing linear energy transfer (LET), and the magnitude of the fast component increases with respect to the slower one. Quenching of the fluorescence by radicals or other transient species produced in the particle track are thought to be responsible for the observations. At low LET the relative yield of the fluorescence decreases with increasing LET, presumably due to the quenching. However, at higher LET the fluorescence yield increases with increasing LET. Self-annihilation reactions of the triplet states to give singlet states may be the source of these observations. These experiments are the first in which the temporal variation of fluorescence emission has been determined in a neat hydrocarbon liquid irradiated with heavy ions.
“…7,8 The total yield of benzene triplet excited state, including intersystem crossing from singlet excimer to the triplet excimer is about 4.8 molecules/100 eV with γ-rays. [7][8][9] The triplet forms an excimer by coupling with a ground-state benzene molecule, which decays with a lifetime of about 4.9 ns. 9 The singlet excited state is thought to be the precursor to molecular hydrogen and acetylene, whereas the triplet excited state is believed to decay to a phenyl radical and H atom.…”
The radiation chemical yields of the products derived from the triplet excited state produced in the radiolysis of liquid benzene with gamma-rays, 10 MeV 4He ions, and 10 MeV 12C ions have been determined. Iodine scavenging techniques have been used to examine the formation and role of radicals, especially the H atom and phenyl radical. For all irradiation types examined here, the increase in hydrogen iodide yields with increasing iodine concentration matches the increase in iodobenzene yields. This agreement suggests that the benzene triplet excited state is the common precursor for the H atom and the phenyl radical. Pulse radiolysis studies in liquid benzene have determined the rate coefficients for the reactions of phenyl radicals with iodine and with the solvent benzene to be 9.3 x 10(9) M(-1) s(-1) and 3.1 x 10(5) M(-1) s(-1), respectively. Direct measurements of polymer formation, which refers to trimers (C18) and higher order compounds (>C18), in liquid benzene radiolysis using gamma-rays, 4He ions, and 12C ions at relatively high doses have been performed using gel permeation chromatography. The yields of trimers increase from gamma-rays to 12C ions due to the increased importance of intratrack radical-radical reactions that can be scavenged by the radical scavenging reactions of iodine. On the other hand, the >C18 product yields decrease from gamma-rays to 12C ions. The structure of the polymer consists of a partly saturated ring as determined by infrared and gas chromatography/mass spectrometry studies. A schematic representation for the radiolytic decomposition of the benzene triplet excited state is presented.
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