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Paramagnetic relaxation characteristics of trapped electrons in γ-irradiated glassy 3-methylpentane (3-MP) at 71°K, and triethylamine (TEA) and methyltetrahydrofuran (MTHF) at 77°K were studied by power saturation techniques. For MTHF and TEA the characteristic relaxation time, (T1T2)1/2, is constant with radiation dose at low doses and decreases at higher doses. For 3-MP the relaxation time decreases even at low dose. Together with data on the total spin concentration the results are interpreted in terms of a ``spur'' model in which the radiation-produced trapped electrons and radicals are trapped in clusters at low dose and constitute a nonuniform spatial distribution. According to this model the spur radius is 〉130 Å in 3 MP, 101 Å in TEA, and 63 Å in MTHF. These radii compare with 58 Å for trapped electrons in glassy methanol and 41 Å in glassy alkaline ice (10M NAOH). For all of these matrices the radius within which the electrons are trapped appears to increase with decreasing polarity of the matrix, and consequently radiation-produced electrons appear to travel farther before being trapped in less polar matrices.

The kinetics of organics purging In the purge-and-trap gas chromatography/mass spectrometry technique for the concentration of volatile compounds In water using primary fragment Ions In modified method 524,2 Is revealed to be first order with respect to purging time. This kinetic model Is applicable from a concentration of 200 ppb for ketones and nitrogen compounds to the sub-ppb levels for more readily purgeable volatile compounds. The purging ratios of the compounds, as well as their first-order purging rate constants, are obtained. The rate constant can be used as an alternative guide to gas chromatographic retention time for the selection of Internal standards for quantitation purposes and/or replacement of surrogates for performance and quality assurance.

Wavelengthselective bleaching of the optical spectra of trapped electrons in organic glasses. II.Electronelectron double resonance study of trapped electrons in γirradiated 2methyltetrahydrofuran glass: Magnetic energy transfer between two different spin systems Electrons are trapped in 'Y irradiated methyltetrahydrofuran (MTHF) glass at 77°K. Monochromatic photoexcitation produces photoconductivity and optical bleaching with a threshold near 780 nrn (1.6 eV) and a peak near 520 nm (2.4 eV). This transition is linear in light intensity and independent of temperature between 77 and 4.2°K, so it is interpreted as a one photon transition directly to the conduction band or to an autoionizing state. Effective double beam photoexcitation discloses a two photon transition which depends on the light intensity squared. The first photon corresponds to the well-known optical absorption of trapped electrons in MTHF at 1.0 eV. This transition is interpreted as a 1s~2p type. The 2p state then presumably crosses to a 2s-type state from which the second photon is absorbed. The wavelength dependence of the second photon transition shows a peak at 950 nm (1.3 eV) and a threshold near 1150 nm (1.1 eV). The temperature of both optical bleaching and photoconductivity under ir photoexcitation shows that population of the 2s-type state involves an activation energy ~O.OOl eV. The deduced energy level structure agrees well with theoretical calculations based on a semicontinuum model for trapped electrons in glassy matrices. Compared to more polar matrices like ice, both experiment and theory indicate that in less polar matrices like MTHF the short-range charge-dipole interactions are relatively less important compared to the long range polarization interactions and cause the bound excited states to be relatively more stable and the ground state to be relatively less stable.

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