Frank K. Truby

Ionic Paramagnetic Species Associated with γ‐Irradiated Amyl Disulfide

ESR and optical bleaching studies of n‐amyl disulfide, γ‐irradiated at 77°K in the amorphous state indicate the presence of ionic paramagnetic species in the irradiated material involving unpaired spins localized mainly at the sulfur. A comparison of ESR derivative peak positions from such samples with those arising from an apparent negative ion species produced from amyl disulfide in a tetrahydrofuran matrix indicates that this species may be common to both types of samples. This finding is supported by the fact that the threshold energy for the destruction of the ionic centers by optical bleaching is the same for both types of samples, being 2.1±0.2 eV. If the ESR spectrum of the negative‐ion species is substracted from the initial ionic species spectrum of amorphous amyl disulfide an ESR line shape is obtained which is postulated to result from a positive‐ion species. The principal g values obtained for this species are 2.003±0.001, 2.035±0.001, and approximately 2.018. Calculated g values based on a m...

Methyl radical kinetics: relaxation versus H-atom abstraction in flash-photolyzed mixtures of methyl iodide and diluent gases☆

Abstract Time-resolved mass spectrometry has been used to deduce the de-excitation rate ( k d ) of photolytically produced “hot” methyl radicals relative to the H-atom abstraction rate ( K a ) from CH 3 1 . The rate-constant ratios k d (M)/ k a f Me = He, Ar, N 2 , and CH 3 l are 0.22 ± 0.02, 0.36 ± 0.03, 0.86 ± 0.13 and 9.6 ± 0.8, respectively.

Laser‐beam characteristics of Phoenix, an HF oscillator‐amplifier system

Energy‐extraction and beam‐quality measurements are reported for Phoenix, Sandia’s high‐energy HF laser system. The final amplifier in this oscillator‐amplifier chain used electron‐beam initiation of high‐pressure gas mixtures of H2‐F2‐O2. The oscillator and preamplifier utilized fast electric discharges in SF6‐HI mixtures. Energy‐extraction efficiency using this oscillator system was the same as that previously determined using an H2‐F2‐O2‐fueled oscillator which produced a better spectral match to the amplifier but which yielded poorer beam quality. Lateral shearing interferograms showed no significant phase‐front degradation of the beam by the final amplifier. Pinhole energy‐transmission measurements using a short‐focal‐length parabolic mirror determined that the focal‐spot diameter was 2.7 times the diffraction‐limited diameter.

Energy Transfer in Irradiated Alkyl Disulfides

An electron spin resonance study was made on a series of gamma- irradiated n-alkyl disulfides to determine the ability of energy imparted randomly to such molecules to be localized at the sulfur. The compounds studied were methyl, amyl, octyl, and octadecyl disulfide. Results showed that all of the compounds contain unpaired electrons localized at the sulfur. The energy imparted to the alkyl disulfides irradiated at - 196 deg C in the ball form appear to migrate down the carbon chain in a manner observed for a - CH/sub 2/- chain. For octadecyl disulfide in the ball form, it is apparent that some C- H breskage occurs before localization can take place at the disulfide link. In the case of slowly crystallized samples, significant C - H breakage is noted for flve or more carbons in the alkyl group, indicating that the crystallographic configuration as well as chain length affects the ability of the energy to be localized at the disulfide link. (N.W.R.)

Energy Migration and Localization Processes in γ‐Irradiated, Amorphous n‐Alkyl Disulfides

It was previously determined that amorphous alkyl disulfides irradiated at 77°K contain ionic species, alkyl radical species, and RS· radical species. The current study has been undertaken in order to determine the relative amounts of these species as a function of alkyl chain length in an effort to understand more clearly the energy migration and localization processes which occur in these compounds. It was found that no significant dependence of alkyl chain length (from methyl disulfide through eicosyl disulfide) occurs for the yield of ion pairs formed as a result of charge migration to the sulfur. This study indicates that essentially all free charge created in these compounds as a result of exposure to ionizing radiation migrates to and localizes at the disulfide group. From examination of the alkyl and RS· radical yields in these compounds as a function of chain length, it appears that excitation also localizes at the disulfide group. However, the localization of excitation at the sulfur group occur...

Effects of chemical kinetics of the performance of the atomic iodine laser system

Model calculations show that chemical reactions which take place in the active medium of a photolytically pumped iodine laser limit the efficiency with which pump photons are utilized and convert significant amounts of the starting material RI to the unwanted by‐products R2 and I2. Laser‐ and rf‐discharge‐based methods for regenerating starting materials from by‐products are evaluated experimentally. For economical operation of large iodine laser systems, CF3I is presently the best starting material, and a pulsed rf‐discharge technique is presently the best one for chemical regeneration. The absorbed energy required to regenerate one CF3I molecule using pulsed rf‐discharge techniques is 5.8 eV.

Spontaneous explosions in multiatmosphere H2‐F2‐O2 mixtures

Explosion studies in multiatmosphere H2‐F2‐O2 mixtures show that the pressures at which such mixtures spontaneously explode are greatly affected by treatment of the explosion cell surfaces prior to filling the cell with H2‐F2‐O2 mixtures. This strong effect of surface conditioning indicates that the observed explosions in H2‐F2‐O2 mixtures (covering a wide range in [F2]/[H2] ratios) with total pressures up to 10 atm result from surface‐associated initiation processes rather than from purely volume‐initiated third‐limit processes. These results agree with a kinetic model involving H2O2 production with a chain formation of H2O at the surface.

Stability of multiatmosphere H2‐F2‐O2 mixtures for HF laser studies

Explosion pressures for multiatmosphere mixtures of H2, F2, and O2 have been obtained. Mixtures exhibiting short‐term stability have been prepared with total pressures up to 11 atm.

Axially‐aligned, photon‐blind, electron‐multiplier arrangement for single‐ion counting with a quadrupole mass filter

A quadrupole mass filter has been equipped with a simply constructed passive electrode aperture arrangement which effectively shields a high‐gain electron multiplier used for single‐pulse counting applications from photon interference.

Rate constants for the reaction of CH3 with N2F4 and NF2

The rate constants for the following reactions have been determined by mass spectrometric measurements following flash photolysis of CH3I/N2F4/(NF2)/N2 gas mixtures: CH3 + N2F4 → CH3NF2 + NF2, k1 = 6.7 ± 0.8 × 10−12 cc/molecule · sec (1), and CH3 + NF2(+M) → CH3NF2, k2 = 2.0 ± 1.1 × 10−12 cc/molecule · sec (2). The measurements were made near room temperature (40 °C) with sufficient N2 buffer gas to insure that only ground‐state methyl radicals were reacting. Changes in the buffer‐gas pressure did not change the observed second‐order rate constant k2. This result is consistent with the rapid HF elimination from CH3NF2 that has been estimated for Reaction (2).