https://www.lpl.arizona.edu/~yelle/eprints/Yelle04b.pdf

Aeronomy of extra-solar giant planets at small orbital distances

A model for the plasma enhanced chemical vapor deposition of amorphous hydrogenated silicon (a‐Si:H) in rf and dc discharges is presented. The model deals primarily with the plasma chemistry of discharges sustained in gas mixtures containing silane (SiH4). The plasma chemistry model uses as input the electron impact rate coefficients generated in a separate simulation for the electron kinetics and therefore makes no a priori assumptions as to the manner of power deposition. Radical densities and contributions to film growth are discussed as a function of gas mixture, electrode separation, and locale of power deposition, and comparisons are made to experiment. A compendium of reactions and rate constants for silane neutral and ion chemistry is also presented.

A model for the discharge kinetics and plasma chemistry during plasma enhanced chemical vapor deposition of amorphous silicon

Observations of H{sup +}{sub 3} in the Galactic diffuse interstellar medium have led to various surprising results, including the conclusion that the cosmic-ray ionization rate ({zeta}{sub 2}) is about one order of magnitude larger than previously thought. The present survey expands the sample of diffuse cloud sight lines with H{sup +}{sub 3} observations to 50, with detections in 21 of those. Ionization rates inferred from these observations are in the range (1.7 {+-} 1.3) Multiplication-Sign 10{sup -16} s{sup -1} < {zeta}{sub 2} < (10.6 {+-} 8.2) Multiplication-Sign 10{sup -16} s{sup -1} with a mean value of {zeta}{sub 2} = (3.5{sup +5.3}{sub -3.0}) Multiplication-Sign 10{sup -16} s{sup -1}. Upper limits (3{sigma}) derived from non-detections of H{sup +}{sub 3} are as low as {zeta}{sub 2} < 0.4 Multiplication-Sign 10{sup -16} s{sup -1}. These low upper limits, in combination with the wide range of inferred cosmic-ray ionization rates, indicate variations in {zeta}{sub 2} between different diffuse cloud sight lines. A study of {zeta}{sub 2} versus N{sub H} (total hydrogen column density) shows that the two parameters are not correlated for diffuse molecular cloud sight lines, but that the ionization rate decreases when N{sub H} increases to values typical of dense molecular clouds. Bothmore » the difference in ionization rates between diffuse and dense clouds and the variation of {zeta}{sub 2} among diffuse cloud sight lines are likely the result of particle propagation effects. The lower ionization rate in dense clouds is due to the inability of low-energy (few MeV) protons to penetrate such regions, while the ionization rate in diffuse clouds is controlled by the proximity of the observed cloud to a site of particle acceleration.« less

https://iopscience.iop.org/article/10.1088/0004-637X/745/1/91/pdf

Investigating the cosmic-ray ionization rate in the galactic diffuse interstellar medium through observations of h+ 3

The selected ion flow tube (SIFT); A technique for studying ion-neutral reactions

We present results from high-resolution three-dimensional simulations of turbulent interstellar gas that self-consistently follow its coupled thermal, chemical and dynamical evolution, with a particular focus on the formation and destruction of H 2 and CO. We quantify the formation time-scales for H 2 and CO in physical conditions corresponding to those found in nearby giant molecular clouds, and show that both species form rapidly, with chemical time-scales that are comparable to the dynamical time-scale of the gas. We also investigate the spatial distributions of H 2 and CO, and how they relate to the underlying gas distribution. We show that H 2 is a good tracer of the gas distribution, but that the relationship between CO abundance and gas density is more complex. The CO abundance is not well-correlated with either the gas number density n or the visual extinction Av : both have a large influence on the CO abundance, but the inhomogeneous nature of the density field produced by the turbulence means that n and A v are only poorly correlated. There is a large scatter in A v , and hence CO abundance, for gas with any particular density, and similarly a large scatter in density and CO abundance for gas with any particular visual extinction. This will have important consequences for the interpretation of the CO emission observed from real molecular clouds. Finally, we also examine the temperature structure of the simulated gas. We show that the molecular gas is not isothermal. Most of it has a temperature in the range of 10-20 K, but there is also a significant fraction of warmer gas, located in low-extinction regions where photoelectric heating remains effective.

Modelling CO formation in the turbulent interstellar medium

Use of ion cyclotron resonance methods to measure the thermal energy rate constants for a number of ion-molecule reactions involving hydrogen and hydrogen-helium mixtures Assuming that the distribution of initial vibrational states in the H2(+) ion is a near-Franck-Condon distribution, the occurrence of collisional deactivation of vibrationally excited H2(+) ions by He atoms is identified, and an approximate rate constant for the deactivation process and its dependence on vibrational energy are given

Ion‐molecule reactions and vibrational deactivation of H2+ ions in mixtures of hydrogen and helium

Ion cyclotron resonance methods are used to identify and to measure the rate constants for the abstraction of a hydrogen atom from H2 by CH+, CH2 +, CH4 +, N+, NH+, NH2 +, NH3 +, O+, OH+, H2O+, CO+, N2 +, C2 +, and C2H+ ions. Although in most cases hydrogen atom abstraction is the only available exothermic pathway for these reactions at thermal energies, the rate constants measured show that except for O+, CO+, and N2 +, a large fraction of collisions between these ions and H2 are not reactive. The rate constants measured range from a low of (3±1) × 10−13 cm3/sec for the NH3 +−H2reaction to (1.73±0.04) × 10−9 cm3/sec for the N2 +−H2reaction. These values compare to the Langevin value of about 1.5 × 10−9 cm3/sec for collisions between these ions and H2. An examination was also made for possible thermoneutral hydrogen atom exchange reactions for those ions which do not react with H2 (CH5 +, CH3 +, NH4 +, H3O+, H2S+, H3S+). The only exchange reaction observed was for collisions between CD3 + ions and H2, for which a rate constant of (5.1±0.5) × 10−10 cm3/sec was measured.

ICR studies of some hydrogen atom abstraction reactions: X+ + H2 → XH+ + H

Reactions of excited and ground state H3+ ions with simple hydrides and hydrocarbons: collisional deactivation of vibrationally excited H3+ ions

Proton transfer reactions from H3+ ions to N2, O2, and CO molecules☆

The reaction of BF3(g) with B2O3(l) was studied by the transpiration method in the temperature range 600° to 1100°K. Results indicate the reaction to be BF 3 ( g )+ B 2 O 3 ( l )=( BOF ) 3 ( g ). ΔH 298° was found to be 4.2 kcal, and leads to ΔHf 298°=—566.8±1 kcal/mole for (BOF)3(g). The vapor above mixtures of MgF2 and B2O3 contained in a Knudsen cell was analyzed with a mass spectrometer and was found to contain BF3(g), (BOF)3(g), and BOF(g) in the range 980° to 1230°K. From studies of the temperature dependence of appropriate ion intensities the heat of the reaction ( BOF ) 3 ( g )=3 BOF ( g ) was derived as 131 kcal at 1125°K. Use of low ionizing electron energies was required to avoid fragmentation effects. The heat of formation of BOF(g) at 298°K was calculated to be —144±3 kcal/mole.

L. P. Theard

Papers

Ion‐molecule reactions and vibrational deactivation of H2+ ions in mixtures of hydrogen and helium

ICR studies of some hydrogen atom abstraction reactions: X+ + H2 → XH+ + H

Reactions of excited and ground state H3+ ions with simple hydrides and hydrocarbons: collisional deactivation of vibrationally excited H3+ ions

Proton transfer reactions from H3+ ions to N2, O2, and CO molecules☆

Transpiration and Mass Spectrometric Studies of Equilibria Involving BOF(g) and (BOF)3(g)