Quantum yields of photoionization in the 308-nm two-photon ionization of solutes in hydrocarbon solutions and their relationship to the observed conductivity signals

Journal Article · Thu Jan 11 04:00:00 EST 1990 · Journal of Physical Chemistry; (USA)

DOI:https://doi.org/10.1021/j100364a040· OSTI ID:6729804

Schmidt, K H; Sauer, Jr, M C

A method is described for measuring the overall quantum yields for free ions in the two-photon ionization of solutes in hydrocarbon liquids and for extracting the quantum yield for production of free ions from solute excited states. The zero electric field quantum yields at 308 nm and 25{degree}C for production of free ions from the singlet state of anthracene in n-hexane, cyclohexane, and isooctane (2,2,4-trimethylpentane) are 0.0023, 0.0058, and 0.017, respectively. Similarly, in isooctane, for the singlet states of fluoranthene, coronene, and TMPD (N,N,N{prime},N{prime}-tetramethyl-p-phenylenediamine), the quantum yields are 0.0039, 0.023, and 0.028, respectively. All of these quantum yields are for solutions saturated with SF{sub 6}{center dot}; in n-hexane and cyclohexane decreasing the concentration of SF{sub 6} by 2 orders of magnitude has no effect, but in isooctane the quantum yield of free ions increases by a factor of 2. The quantum yield results obtained with light of 308 nm are used in conjunction with measurements of the decay of conductivity due to the geminate ion pairs to obtain information on the distance distribution within the geminate pairs and the primary yield of photoionization. The analysis indicates that the primary quantum yields for ionization of the first excited singlet state of anthracene are approximately unit for isooctane and cyclohexane solutions, but may be as low as 0.4 for anthracene in n-hexane, and that an r{sup 2} Gaussian or f{sup 2} exponential distribution of separation distances explains the experimental observations better than an exponential distribution. Comparison with results obtained in radiolysis with electrons shows that the distribution of separation distances is narrower in the photochemical case, resulting in lower probability for separation into free ions.

• DOE Contract Number: W-31109-ENG-38
• OSTI ID: 6729804
• Journal Information: Journal of Physical Chemistry; (USA), Journal Name: Journal of Physical Chemistry; (USA) Vol. 94:1; ISSN 0022-3654; ISSN JPCHA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400500* -- Photochemistry
CALCULATION METHODS
DATA
DATA ANALYSIS
EFFICIENCY
EXPERIMENTAL DATA
HYDROCARBONS
INFORMATION
IONIZATION
MEASURING INSTRUMENTS
MEASURING METHODS
NUMERICAL DATA
ORGANIC COMPOUNDS
PHOTOIONIZATION
QUANTUM EFFICIENCY
SOLUTES