Jeffrey F. Friedman

Pressure and temperature dependence of dissociative and non-dissociative electron attachment to CF3: Experiments and kinetic modeling

The kinetics of electron attachment to CF(3) as a function of temperature (300-600 K) and pressure (0.75-2.5 Torr) were studied by variable electron and neutral density attachment mass spectrometry exploiting dissociative electron attachment to CF(3)Br as a radical source. Attachment occurs through competing dissociative (CF(3) + e(-) → CF(2) + F(-)) and non-dissociative channels (CF(3) + e(-) → CF(3)(-)). The rate constant of the dissociative channel increases strongly with temperature, while that of the non-dissociative channel decreases. The rate constant of the non-dissociative channel increases strongly with pressure, while that of the dissociative channel shows little dependence. The total rate constant of electron attachment increases with temperature and with pressure. The system is analyzed by kinetic modeling in terms of statistical theory in order to understand its properties and to extrapolate to conditions beyond those accessible in the experiment.

Electron attachment to Ni(PF3)4 and Pt(PF3)4

An experimental study has been made of thermal electron attachment to the transition-metal trifluorophosphine complexes Ni(PF(3))(4) and Pt(PF(3))(4) using a flowing-afterglow Langmuir-probe apparatus. Both complexes are efficient at electron attachment, although the rate constants are somewhat less than collisional. The rate constant for electron attachment to Ni(PF(3))(4) is 1.9 x 10(-7) cm(3) s(-1) at room temperature, about a factor of 2 less than collisional. The activation energy is 39+/-5 meV for the attachment reaction. The rate constant for electron attachment to Pt(PF(3))(4) is 5.4 x 10(-8) cm(3) s(-1) at room temperature, and the activation energy is 84+/-8 meV. For both complexes, a PF(3) ligand is lost on electron attachment, and only the M(PF(3))(3)(-) ion is observed in the negative-ion mass spectrum. Density functional calculations were carried out on Ni(PF(3))(4) and various fragments in order to describe the thermochemistry of the attachment reaction.

Electron attachment to halomethanes at high temperature: CH2Cl2, CF2Cl2, CH3Cl, and CF3Cl attachment rate constants up to 1100 K

We have used a high-temperature flowing-afterglow Langmuir-probe apparatus to measure rate constants for electron attachment to halomethanes which attach electrons very inefficiently at room temperature, yielding Cl(-) ion product. We studied CH(2)Cl(2) (495-973 K), CF(2)Cl(2) (291-1105 K), and CF(3)Cl (524-1004 K) and include our recent measurement for CH(3)Cl (700-1100 K) in the discussion of the electron attachment results. The measured attachment rate constants show Arrhenius behavior in the temperature ranges examined, from which estimates of rate constants at 300 K may be made: CH(2)Cl(2) (1.8x10(-13) cm(3) s(-1)), CH(3)Cl (1.1x10(-17) cm(3) s(-1)), and CF(3)Cl (4.2x10(-14) cm(3) s(-1)), all of which are difficult to measure directly. In the case of CF(2)Cl(2), the room temperature rate constant was sufficiently large to be measured (1.6x10(-9) cm(3) s(-1)). The Arrhenius plots yield activation energies for the attachment reactions: 390+/-50 meV (CH(2)Cl(2)), 124+/-20 meV (CF(2)Cl(2)), 670+/-70 meV (CH(3)Cl), and 406+/-50 meV (CF(3)Cl). Comparisons are made with existing data where available. G3 calculations were carried out to obtain reaction energetics. They show that the parent anions of CH(2)Cl(2) CF(2)Cl(2), CH(3)Cl, and CF(3)Cl are stable, though CH(3)Cl(-) exists only as an electrostatically bound complex.

A New Instrument for Thermal Electron Attachment at High Temperature: NF3 and CH3Cl Attachment Rate Constants up to 1100 K

A new high temperature flowing afterglow Langmuir probe (HT-FALP) apparatus is described. A movable Langmuir probe and a four-needle reactant gas inlet were fitted to an existing high temperature flowing afterglow apparatus. The instrument is suitable for study of electron attachment from 300-1200 K, the upper limit set to avoid softening of the quartz flow tube. We present results for two reactions over extended ranges: NF(3) (300-900 K) and CH(3)Cl (600-1100 K). Electron attachment rate constants for NF(3) had been measured earlier using our conventional FALP apparatus. Those measurements were repeated with the FALP and then extended to 900 K with the HT-FALP. CH(3)Cl attaches electrons too weakly to study with the low temperature FALP but reaches a value of approximately 10(-9) cm(3) s(-1) at 1100 K. F(-) is produced in NF(3) attachment at all temperatures and Cl(-) in CH(3)Cl attachment, as determined by a quadrupole mass spectrometer at the end of the flow tube. Future modifications to increase the plasma density should allow study of electron-ion recombination at high temperatures.

Temperature dependences of rate coefficients for electron catalyzed mutual neutralization

The flowing afterglow technique of variable electron and neutral density attachment mass spectrometry (VENDAMS) has recently yielded evidence for a novel plasma charge loss process, electron catalyzed mutual neutralization (ECMN), i.e., A(+) + B(-) + e(-) → A + B + e(-). Here, rate constants for ECMN of two polyatomic species (POCl(3)(-) and POCl(2)(-)) and one diatomic species (Br(2)(-)) each with two monatomic cations (Ar(+)and Kr(+)) are measured using VENDAMS over the temperature range 300 K-500 K. All rate constants show a steep negative temperature dependence, consistent with that expected for a three body process involving two ions and an electron. No variation in rate constants as a function of the cation type is observed outside of uncertainty; however, rate constants of the polyatomic anions (~1 × 10(-18) cm(6) s(-1) at 300 K) are measurably higher than that for Br(2)(-) [(5.5 ± 2) × 10(-19) cm(6) s(-1) at 300 K].

Gossamer Membrane Telescope

Diffraction grating microstructures covering a flat surface are effective in concentrating flux, but their angles of wavefront reconstruction at a secondary receiver are wavelengthdependent. By designing a secondary that exploits this wavelength dependency, we have invented an entirely new class of telescope, called a Dittoscope, which can acquire millions of high resolution spectra in an observation cycle. A diffraction grating primary objective is well suited for realization on a gossamer membrane substrate, since the effective optics are structures of wavelength proportions. Rigid framing structures that hold the membrane can take advantage of the tendency of the interior tensile membranes to generate flats. The gossamer membrane substrate need only provide sufficient tensile strength to withstand stretching forces and have flatness tolerances that correspond to the spectral resolution.

Kilometer scale primary collector telescopy

We present an improved model for a spectrographic survey telescope with a kilometer scale diffraction grating collector. Refining the initial public disclosures, the new model quantifies flux collection for telescopes of this type. An option in the new model allows a trade of reduced spectral bandwidth for increased flux collection. We provide experimental evidence to demonstrate an earlier prediction of Ångstrom spectral resolution with relaxed tolerances for grating flatness, and we show how this model is extensible in two dimensions.

Electron attachment to sulfur oxyhalides: SOF2, SOCl2, SO2F2, SO2Cl2, and SO2FCl attachment rate coefficients, 300–900 K

Electron attachment to SOF(2), SOCl(2), SO(2)F(2), SO(2)FCl, and SO(2)Cl(2) was studied with two flowing-afterglow Langmuir-probe apparatuses over the temperature range 300-900 K. Attachment rate coefficients at 300 K are k(a) = 2.6+/-0.8x10(-10)(SOF(2)), 1.8+/-0.5x10(-8)(SOCl(2)), 4.8+/-0.7x10(-10)(SO(2)F(2)), 2.4+/-0.7x10(-9)(SO(2)Cl(2)), and 2.0+/-0.6x10(-7) cm(3) s(-1)(SO(2)FCl). Arrhenius plots of the data imply activation energies of 56+/-22 meV(SOF(2)), 92+/-40(SO(2)F(2)), 44+/-22 meV(SOCl(2)), and 29+/-15 meV(SO(2)Cl(2)). The rate coefficients for SO(2)FCl decrease slightly with temperature, commensurate with the decrease in the capture rate coefficient. Electron attachment to SOF(2) and SO(2)F(2) is nondissociative, while reaction with SOCl(2), SO(2)FCl, and SO(2)Cl(2) is dissociative. Dissociative attachment is dominated by channels arising from S-Cl bond cleavage but also includes a minor channel forming a dihalide product ion. Branching fraction data are reported for the dissociative attachment channels.

Rate constants for the reactions of CO3− and O3− with SO2 from 300to1440K

Rate constants for the reactions of CO3− and O3− with SO2 have been measured between 300 and 1440K in a high temperature flowing afterglow apparatus. The CO3− rate constants near to the collision rate at low temperatures and fall by about a factor of 50 with temperature until a broad minimum is reached at 900–1300K. The highest temperature point shows the increasing rate constant. Comparison to drift tube data taken in a helium buffer shows that total energy controls the reactivity, presumably because the reaction goes through a long lived complex even at 1440K. The reaction of O3− with SO2 was studied up to 1400K. The rate constant is collisional until 700K and then decreases with increasing temperature. Rate constants measured at 1300 and 1400K appear to show an increase, but that observation is questionable since O3− could not be made cleanly. The O3− data at 1200K and below show that total energy controls reactivity in that range.

Astronomical telescope with holographic primary objective

A dual dispersion telescope with a plane grating primary objective was previously disclosed that can overcome intrinsic chromatic aberration of dispersive optics while allowing for unprecedented features such as million object spectroscopy, extraordinary étendue, flat primary objective with a relaxed figure tolerance, gossamer membrane substrate stowable as an unsegmented roll inside a delivery vehicle, and extensibility past 100 meter aperture at optical wavelengths. The novel design meets many criteria for space deployment. Other embodiments are suitable for airborne platforms as well as terrestrial and lunar sites. One problem with this novel telescope is that the grazing exodus configuration necessary to achieve a large aperture is traded for throughput efficiency. Now we show how the hologram of a point source used in place of the primary objective plane grating can improve efficiency by lowering the diffraction angle below grazing exodus. An intermediate refractive element is used to compensate for wavelength dependent focal lengths of the holographic primary objective.