The fluorescence action spectra of some saturated hydrocarbon liquids for excitation energies above and below their ionization thresholds

Journal Article · Thu Apr 01 04:00:00 EST 1993 · Journal of Chemical Physics; (United States)

DOI:https://doi.org/10.1063/1.464890· OSTI ID:6688263

Ostafin, A E; Lipsky, S ^[1]

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1. Department of Chemistry, University of Minnesota, Minneapolis, Minnesota 55455 (United States)

Fluorescence action spectra have been obtained for the neat liquids, [ital cis]-decalin, [ital trans]-decalin, bicyclohexyl, cyclohexane, methylcyclohexane, isobutylcyclohexane, 2,3,4-trimethylpentane, 2,3-dimethylbutane, 3-methylhexane, 3-methylpentane, [ital n]-decane, [ital n]-dodecane, and [ital n]-pentadecane at excitation energies, [epsilon], ranging from their absorption onsets (at ca. 7 eV) to 10.3 eV. For all compounds, with the exception of [ital cis]-decalin, the fluorescence quantum yield is observed to monotonically decline with increasing [epsilon], reaching a minimum value at an energy, [epsilon][sub [ital m]] (a few tenths of an eV above the liquid phase ionization threshold, [epsilon][sub [ital l]]) followed by a slow increase. In the case of [ital cis]-decalin, the fluorescence quantum yield remains constant over the entire range of excitation energies studied, permitting its use as a quantum counter replacing the standard sodium salicylate, at least over a spectral range from 185 to 120 nm. The recovery of the fluorescence quantum yield for [epsilon][gt][epsilon][sub [ital m]] is attributed to an increasing probability for electron ejection followed by [ital e][sup [minus]]+RH[sup +] geminate recombination, to produce an excited state of RH with energy less than [epsilon][sub [ital l]]. From a simple analysis of the action spectrum, a lower bound estimate of the electron ejection probability, [phi][sub [plus minus]], is obtained as a function of [epsilon]. In the case of cyclohexane, where [phi][sub [plus minus]] has been obtained by other techniques at [epsilon][congruent]10 eV, the lower bound estimate agrees with the experimental value. From this agreement, arguments are presented to make plausible the conjecture that in all these liquids, the initially produced [ital e][sup [minus]]+RH[sup +] geminate ion pair first rapidly internally converts to an ion-pair state ca.

• OSTI ID: 6688263
• Journal Information: Journal of Chemical Physics; (United States), Journal Name: Journal of Chemical Physics; (United States) Vol. 98:7; ISSN JCPSA6; ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

664200* -- Spectra of Atoms & Molecules & their Interactions with Photons-- (1992-)
74 ATOMIC AND MOLECULAR PHYSICS
ALKANES
ALKYL RADICALS
BUTANE
CYCLOALKANES
CYCLOHEXANE
DECALIN
DECANE
DODECANE
ENERGY
ENERGY DEPENDENCE
ENERGY-LEVEL TRANSITIONS
EXCITATION
FLUIDS
FLUORESCENCE
HEXANE
HEXYL RADICALS
HYDROCARBONS
IONIZATION POTENTIAL
ISOBUTYL RADICALS
LIQUIDS
LUMINESCENCE
METHYL RADICALS
ORGANIC COMPOUNDS
PENTANE
RADICALS
SATURATION
THRESHOLD ENERGY