Excited Singlet-State Yields in Hydrocarbon Liquids Exposed to X-rays

Abstract

The yields of excited singlet states formed in some liquid hydrocarbons are reported for exposure to synchrotron X-rays of energies between 5 and 14 keV. The yields are derived from measurements of ultraviolet fluorescence emission of the hydrocarbons. Results reported are relative to the yield of excited singlets in liquid benzene. The yields decrease with decreasing X-ray energy, and at the lowest energies studied G(1S*) = 1.5/100 eV for cis- and trans-decalin. Results are compared to computer simulations.

Radiation Chemistry of Organic Liquids: Saturated Hydrocarbons

“…Computations show that these quenching reactions can be a significant mechanism of disappearance of the singlet excited states [65], and experimental evidence has been obtained supporting the reduced production of solute S 1 states in spurs of 20-100 eV photons due to the quenching [32,62,65]. Shortening of the solvent S 1 state lifetime with increasing excitation photon energy was observed in radiolysis of cis-decalin and n-dodecane with 4-to-14 keV xrays [83]. This shortening was accounted for by quenching of the alkane S 1 states by alkyl radicals generated in the same spurs.…”

Radiation chemistry of organic liquids: Saturated hydrocarbons

“…The S 1 state lives between 0.5 ns and 2 ns; this lifetime is longer (3-5 ns) for long-chain paraffins [92,94]. In multiple-pair spurs, the S 1 state lifetimes are shortened due to quenching of the excited state by radiolytic products [83]. Eventually, the S 1 state either fragments via reaction (6) or crosses to another excited state, possibly T 1 [92] or S 2 [95]; the radiative decay is very inefficient (< 1%).…”

“…Radiolytic yields of the solvent S 1 states and free ions upon excitation of decalins and n-dodecane using 4 keV to 15 keV photons have been measured [83,90]. Even in this energy regime (where the Monte-Carlo calculations gave good estimates of the free ion yield), agreement between the calculated and measured yields was observed for one solvent only, cis-decalin.…”

“…Shortening of the solvent S 1 state lifetime with increasing excitation photon energy was observed in radiolysis of cis-decalin and n-dodecane with 4-to-14 keV xrays [83]. This shortening was accounted for by quenching of the alkane S 1 states by alkyl radicals generated in the same spurs.…”

7 Radiation chemistry

“…However, the dependence on the energy is greater than expected, particularly for trans-decalin, as if combination of uncorrelated ions in the denser tracks would produce more triplet excited states at the expense of singlet excited states. 124 The absolute excited state singlet yield in pure benzene, derived from results in benzene solutions irradiated by g-or X-ray photons of energy varying from 17.5 to 122 keV, has been determined using a liquid scintillation method. The yield does increase with the photon energy from 0.98 to 1.15 excited states per 100 eV absorbed, the effect being assigned to track effects.…”