Column Density Measurements Research Articles

CO AND H2 ABSORPTION IN THE AA TAURI CIRCUMSTELLAR DISK*

ABSTRACT The direct study of molecular gas in inner protoplanetary disks is complicated by uncertainties in the spatial distribution of the gas, the time variability of the source, and the comparison of observations across a wide range of wavelengths. Some of these challenges can be mitigated with far-ultraviolet spectroscopy. Using new observations obtained with the Hubble Space Telescope Cosmic Origins Spectrograph, we measure column densities and rovibrational temperatures for CO and H2 observed on the line of sight through the AA Tauri circumstellar disk. CO A – X absorption bands are observed against the far-UV continuum. The CO absorption is characterized by log10(N(12CO)) = 17.5 ± 0.5 cm−2 and T rot(CO) = 500+500 −200 K, although this rotational temperature may underestimate the local kinetic temperature of the CO-bearing gas. We also detect 13CO in absorption with an isotopic ratio of ∼20. We do not observe H2 absorption against the continuum; however, hot H2 (v > 0) is detected in absorption against the Lyα emission line. We measure the column densities in eight individual rovibrational states, determining a total log10(N(H2)) = 17.9+0.6 −0.3 cm−2 with a thermal temperature of T(H2) = 2500+800 −700 K. The high temperature of the molecules, the relatively small H2 column density, and the high inclination of the AA Tauri disk suggest that the absorbing gas resides in an inner disk atmosphere. If the H2 and CO are cospatial within a molecular layer ∼0.6 AU thick, this region is characterized by ∼ 105 cm−3 with an observed 〈CO/H2〉 ratio of ∼0.4. We also find evidence for a departure from a purely thermal H2 distribution, suggesting that excitation by continuum photons and H2 formation may be altering the level populations in the molecular gas.

X-RAY SPECTROSCOPY OF AS1101 WITHCHANDRA,XMM-NEWTON, ANDROSAT: BANDPASS DEPENDENCE OF THE TEMPERATURE PROFILE AND SOFT EXCESS EMISSION

We present spatially-resolved spectroscopy of the galaxy cluster Abell S1101, also known as Sersic 159-03, with Chandra, XMM-Newton and ROSAT, and investigate the presence of soft X-ray excess emission above the contribution from the hot intra-cluster medium. In earlier papers we reported an extremely bright soft excess component that reached 100% of the thermal radiation in the R2 ROSAT band (0.2-0.4 keV), using the HI column density measurement by Dickey and Lockman. In this paper we use the newer Leiden-Argentine-Bonn survey measurements of the HI column density towards Abell S1101, significantly lower than the previous value, and show that the soft excess emission in Abell S1101 is now at the level of 10-20% of the hot gas emission, in line with those of a large sample of clusters analyzed by Bonamente et al. in 2002. The ROSAT soft excess emission is detected regardless of calibration uncertainties between Chandra and XMM-Newoton. This new analysis of Abell S1101 indicate that the 1/4keV band emission is compatible with the presence of WHIM filaments connected to the cluster and extending outward into the intergalactic medium; the temperatures we find in this study are typically lower than the WHIM probed in other X-ray studies. We also show that the soft excess emission is compatible with a non-thermal origin as the inverse Compton scattering of relativistic electrons off the cosmic microwave background, with pressure less than 1% of the thermal electrons.

A COMPTON-THICK ACTIVE GALACTIC NUCLEUS AT z ∼ 5 IN THE 4 Ms CHANDRA DEEP FIELD SOUTH

We report the discovery of a Compton-thick Active Galactic Nucleus (AGN) at z=4.76 in the 4 Ms Chandra Deep Field South. This object was selected as a V-band dropout in HST/ACS images and previously recognized as an AGN from optical spectroscopy. The 4 Ms Chandra observations show a significant (~4.2sigma) X-ray detection at the V-band dropout position. The X-ray source displays a hardness ratio of HR=0.23+-0.24, which, for a source at z~5, is highly suggestive of Compton-thick absorption. The source X-ray spectrum is seen above the background level in the energy range of ~0.9-4 keV, i.e., in the rest-frame energy range of ~5-23 keV. When fixing the photon index to Gamma=1.8, the measured column density is N_H=1.4^{+0.9}_{-0.5} x 10^{24} cm^{-2}, which is Compton-thick. To our knowledge, this is the most distant heavily obscured AGN, confirmed by X-ray spectral analysis, discovered so far. The intrinsic (de-absorbed), rest-frame luminosity in the 2-10 keV band is ~2.5 x 10^{44} erg s^{-1}, which places this object among type-2 quasars. The Spectral Energy Distribution shows that massive star formation is associated with obscured black hole accretion. This system may have then been caught during a major co-eval episode of black hole and stellar mass assembly at early times. The measure of the number density of heavily obscured AGN at high redshifts will be crucial to reconstruct the BH/galaxy evolution history from the beginning.

Direct satellite observation of lightning-produced NO<sub>x</sub>

Abstract. Lightning is an important source of NOx in the free troposphere, especially in the tropics, with strong impact on ozone production. However, estimates of lightning NOx (LNOx) production efficiency (LNOx per flash) are still quite uncertain. In this study we present a systematic analysis of NO2 column densities from SCIAMACHY measurements over active thunderstorms, as detected by the World-Wide Lightning Location Network (WWLLN), where the WWLLN detection efficiency was estimated using the flash climatology of the satellite lightning sensors LIS/OTD. Only events with high lightning activity are considered, where corrected WWLLN flash rate densities inside the satellite pixel within the last hour are above 1 /km2/h. For typical SCIAMACHY ground pixels of 30 × 60 km2, this threshold corresponds to 1800 flashes over the last hour, which, for literature estimates of lightning NOx production, should result in clearly enhanced NO2 column densities. From 2004–2008, we find 287 coincidences of SCIAMACHY measurements and high WWLLN flash rate densities. For some of these events, a clear enhancement of column densities of NO2 could be observed, indeed. But overall, the measured column densities are below the expected values by more than one order of magnitude, and in most of the cases, no enhanced NO2 could be found at all. Our results are in contradiction to the currently accepted range of LNOx production per flash of 15 (2–40)×1025 molec/flash. This probably partly results from the specific conditions for the events under investigation, i.e. events of high lightning activity in the morning (local time) and mostly (for 162 out of 287 events) over ocean. Within the detected coincidences, the highest NO2 column densities were observed around the US Eastcoast. This might be partly due to interference with ground sources of NOx being uplifted by the convective systems. However, it could also indicate that flashes in this region are particularly productive. We conclude that current estimates of LNOx production might be biased high for two reasons. First, we observe a high variability of NO2 for coincident lightning events. This high variability can easily cause a publication bias, since studies reporting on high NOx production have likely been published, while studies finding no or low amounts of NOx might have been rejected as errorneous or not significant. Second, many estimates of LNOx production in literature have been performed over the US, which is probably not representative for global lightning.

HOT GAS IN THE GALACTIC THICK DISK AND HALO NEAR THE DRACO CLOUD

This paper examines the ultraviolet and X-ray photons generated by hot gas in the Galactic thick disk or halo in the Draco region of the northern hemisphere. Our analysis uses the intensities from four ions, C IV, O VI, O VII, and O VIII, sampling temperatures of ~100,000 to ~3,000,000 K. We measured the O VI, O VII and O VIII intensities from FUSE and XMM-Newton data and subtracted off the local contributions in order to deduce the thick disk/halo contributions. These were supplemented with published C IV intensity and O VI column density measurements. Our estimate of the thermal pressure in the O VI-rich thick disk/halo gas, p_{th}/k = 6500^{+2500}_{-2600} K cm^{-3}, suggests that the thick disk/halo is more highly pressurized than would be expected from theoretical analyses. The ratios of C IV to O VI to O VII to O VIII, intensities were compared with those predicted by theoretical models. Gas which was heated to 3,000,000 K then allowed to cool radiatively cannot produce enough C IV or O VI-generated photons per O VII or O VIII-generated photon. Producing enough C IV and O VI emission requires heating additional gas to 100,000 < T < 1,000,000 K. However, shock heating, which provides heating across this temperature range, overproduces O VI relative to the others. Obtaining the observed mix may require a combination of several processes, including some amount of shock heating, heat conduction, and mixing, as well as radiative cooling of very hot gas.

Larson's third law and the universality of molecular cloud structure

Larson (1981) first noted a scaling relation between masses and sizes in molecular clouds that implies that these objects have approximately constant column densities. This original claim, based upon millimeter observations of carbon monoxide lines, has been challenged by many theorists, arguing that the apparent constant column density observed is merely the result of the limited dynamic range of observations, and that in reality clouds have column density variations over two orders of magnitudes. In this letter we investigate a set of nearby molecular clouds with near-infrared excess methods, which guarantee very large dynamic ranges and robust column density measurements, to test the validity of Larson's third law. We verify that different clouds have almost identical average column densities <i>above a given extinction threshold <i/>; this holds regardless of the extinction threshold, but the actual average surface mass density is a function of the specific threshold used. We show that a second version of Larson's third law, involving the mass-radius relation for single clouds and cores, does not hold in our sample, indicating that individual clouds are not objects that can be described by constant column density. Our results instead indicate that molecular clouds are characterized by a universal structure. Finally we point out that this universal structure can be linked to the log-normal nature of cloud column density distributions.

COSMIC ORIGINS SPECTROGRAPH OBSERVATIONS OF TRANSLUCENT CLOUDS: Cyg OB2 8A

Data from the Cosmic Origins Spectrograph (COS) are presented for the first highly reddened target (Cyg OB2 8A) under the COS Science Team's guaranteed time allocation. Column densities of ionic, atomic, and molecular species are reported and implications are discussed. Data from Cyg OB2 8A demonstrate the ability to analyze highly reddened interstellar sight lines with the COS that were unavailable to previous UV instruments. Measured column densities indicate that the Cyg OB2 8A line of sight contains multiple diffuse clouds rather than a dominant translucent cloud.

ACCURATE LABORATORY WAVELENGTHS OF THE e 3 Σ – (ν′ = 5) – X 1 Σ + (ν″ = 0) BAND OF 12 C 16 O

The forbidden singlet-triplet transitions of carbon monoxide (CO) are important in the interpretation of vacuum ultraviolet interstellar absorption spectra and in particular for the measurement of large CO column densities. Twenty rovibronic lines of the e 3Σ–(ν' = 5) – X 1Σ+(ν'' = 0) band of 12 C 16O for which laboratory wavelengths were previously unavailable were identified in laser-induced fluorescence excitation spectra. Wavelengths were assigned to five rovibronic transitions to an average accuracy of 0.0028 A. A further 15 lines could not be fully resolved and average wavelengths were measured for these groups of closely spaced lines. A wavelength difference of 0.011 ± 0.0028 A between the measured wavelengths and the calculated wavelengths in the atlas of Eidelsberg & Rostas demonstrates the need for more experimental data on CO.

2MASS wide field extinction maps

We present a near-infrared extinction map of a large region in the sky (∼3500 deg 2 ) in the general directions of Taurus, Perseus, and Aries. The map has been obtained using robust and optimal methods to map dust column density at near-infrared wavelengths (Nicer, described in Lombardi & Alves 2001, AA we name this region the Perseus-Andromeda hole. We find that over the region that encompasses the Taurus, Perseus, and California clouds the column density measurements below AK < 0.2 mag are perfectly described by a log-normal distribution, and that a significant deviation is observed at larger extinction values. If turbulence models are invoked to justify the log-normal distribution, the observed departure could be interpreted as the result of the effect of gravity that acts on the cores of the clouds. Finally, we investigate the cloud structure function, and show that significant deviations from the results predicted by turbulent models are observed in at least one cloud.

Pulsed airborne lidar measurements of atmospheric CO2 column absorption

We report initial measurements of atmospheric CO2 column density using a pulsed airborne lidar operating at 1572 nm. It uses a lidar measurement technique being developed at NASA Goddard Space Flight Center as a candidate for the CO2 measurement in the Active Sensing of CO2 Emissions over Nights, Days and Seasons (ASCENDS) space mission. The pulsed multiple-wavelength lidar approach offers several new capabilities with respect to passive spectrometer and other lidar techniques for high-precision CO2 column density measurements. We developed an airborne lidar using a fibre laser transmitter and photon counting detector, and conducted initial measurements of the CO2 column absorption during flights over Oklahoma in December 2008. The results show clear CO2 line shape and absorption signals. These follow the expected changes with aircraft altitude from 1.5 to 7.1 km, and are in good agreement with column number density estimates calculated from nearly coincident airborne in-situ measurements.

DETECTION OF A SUPERSTRONG 2175 Å ABSORPTION GALAXY ATz= 0.8839 TOWARD THE QUASAR SDSS J100713.68+285348.4

We report a superstrong 2175 angstrom absorption galaxy at a redshift of z(G) = 0.8839 toward the background quasar SDSS J100713.68+285348.4 at z(Q) = 1.047 identified from the Sloan Digital Sky Survey (SDSS) data. The bump is the strongest ever known, about 2.5 times the average in the Galactic interstellar extinction curves. About two dozens of narrow absorption lines are identified in this system in the SDSS and the follow-up Multiple Mirror Telescope (MMT) spectra, including Zn II, Cr II, Mn II, Si II, Fe II, Ti II, Ca II, Al III, Mg II, and Mg I. We have derived accurate measurements of the gas-phase column densities of most of these ions through their weak absorption lines. The combination of unprecedentedly strong 2175 angstrom absorption bump strength with the measured zinc column density suggests that carbon is likely to be the main carrier of the 2175 angstrom absorber assuming that the total abundance of the absorber relative to zinc is similar to the solar values and zinc is not heavily depleted onto dust grains. Under the same assumption, we found that dust depletion in this absorption galaxy is much less than that in the Milky Way, indicating possible different nucleosynthesis and/or chemical and interstellar medium evolution history.

Detection of pollution transport events southeast of Mexico City using ground-based visible spectroscopy measurements of nitrogen dioxide

Abstract. This work presents ground based differential optical absorption spectroscopy (DOAS) measurements of nitrogen dioxide (NO2) during the MILAGRO field campaign in March 2006 at the Tenango del Aire research site located to the southeast of Mexico City. The DOAS NO2 column density measurements are used in conjunction with ceilometer, meteorological and surface nitric oxide (NO), nitrogen oxides (NOx) and total reactive nitrogen (NOy) measurements to analyze pollution transport events to the southeast of Mexico City during the MILARGO field campaign. The study divides the data set into three case study pollution transport events that occurred at the Tenango del Aire research site. The unique data set is then used to provide an in depth analysis of example days of each of the pollution transport events. An in depth analysis of 13 March 2006, a Case One day, shows the transport of several air pollution plumes during the morning through the Tenango del Aire research site when southerly winds are present and demonstrates how DOAS tropospheric NO2 vertical column densities (VCD), surface NO2 mixing ratios and ceilometer data are used to determine the vertical homogeneity of the pollution layer. The analysis of 18 March 2006, a Case Two day, shows that when northerly winds are present for the entire day, the air at the Tenango del Aire research site is relatively clean and no major pollution plumes are detected. Case 3 days are characterized by relatively clean air throughout the morning with large DOAS NO2 enhancements detected in the afternoon. The analysis of 28 March 2006 show the DOAS NO2 enhancements are likely due to lightning activity and demonstrate how suitable ground-based DOAS measruements are for monitoring anthropogenic and natural pollution sources that reside above the mixing layer.

Using X-ray observations to explore the binary interaction in Eta Carinae

We study the usage of the X-ray light curve, column density toward the hard X-ray source, and emission measure (density square times volume), of the massive binary system Eta Carinae to determine the orientation of its semi-major axis. The source of the hard X-ray emission is the shocked secondary wind. We argue that, by itself, the observed X-ray flux cannot teach us much about the orientation of the semi-major axis. Minor adjustment of some unknown parameters of the binary system allows to fit the X-ray light curve with almost any inclination angle and orientation. The column density and X-ray emission measure, on the other hand, impose strong constrains on the orientation. We improve our previous calculations and show that the column density is more compatible with an orientation where for most of the time the secondary - the hotter, less massive star - is behind the primary star. The secondary comes closer to the observer only for a short time near periastron passage. The ten-week X-ray deep minimum, which results from a large decrease in the emission measure, implies that the regular secondary wind is substantially suppressed during that period. This suppression is most likely resulted by accretion of mass from the dense wind of the primary luminous blue variable (LBV) star. The accretion from the equatorial plane might lead to the formation of a polar outflow. We suggest that the polar outflow contributes to the soft X-ray emission during the X-ray minimum; the other source is the shocked secondary wind in the tail. The conclusion that accretion occurs at each periastron passage, every five and a half years, implies that accretion had occurred at a much higher rate during the 20 Great Eruption of Eta Carinae in the 19th century.

Diffuse molecular gas at high redshift

We present the detection of carbon monoxide molecules (CO) at z=1.6408 towards the quasar SDSSJ160457.50+220300.5 using the VLT Ultraviolet and Visual Echelle Spectrograph. CO absorption is detected in at least two components in the first six A-X bands and one d-X(5-0) inter-band system. This is the second detection of this kind along a quasar line of sight. The CO absorption profiles are well modelled assuming a rotational excitation of CO in the range 6<Tex<16 K, which is consistent with or higher than the temperature of the CMB radiation at this redshift. We derive a total CO column density of N(CO)=4e14 cm^-2. The measured column densities of SI, MgI, ZnII, FeII and SiII indicate a dust depletion pattern typical of cold gas in the Galactic disc. The background quasar spectrum is significantly reddened (u-K~4.5 mag) and presents a pronounced 2175 A dust absorption feature at the redshift of the CO absorber. Using a control sample of ~500 quasars we find the chance probability for this feature to be spurious is ~0.3%. We show that the SED of the quasar is well fitted with a QSO composite spectrum reddened with a LMC supershell extinction law at the redshift of the absorber. It is noticeable that this quasar is absent from the colour-selected SDSS quasar sample. This demonstrates our current view of the Universe may be biased against dusty sightlines. These direct observations of carbonaceous molecules and dust open up the possibility of studying physical conditions and chemistry of diffuse molecular gas in high redshift galaxies.

Imaging sensor constellation for tomographic chemical cloud mapping

A sensor constellation capable of determining the location and detailed concentration distribution of chemical warfare agent simulant clouds has been developed and demonstrated on government test ranges. The constellation is based on the use of standoff passive multispectral infrared imaging sensors to make column density measurements through the chemical cloud from two or more locations around its periphery. A computed tomography inversion method is employed to produce a 3D concentration profile of the cloud from the 2D line density measurements. We discuss the theoretical basis of the approach and present results of recent field experiments where controlled releases of chemical warfare agent simulants were simultaneously viewed by three chemical imaging sensors. Systematic investigations of the algorithm using synthetic data indicate that for complex functions, 3D reconstruction errors are less than 20% even in the case of a limited three-sensor measurement network. Field data results demonstrate the capability of the constellation to determine 3D concentration profiles that account for ~?86%? of the total known mass of material released.

Radiation pressure and absorption in AGN: results from a complete unbiased sample from Swift

Abstract Outward radiation pressure can exceed the inward gravitational pull on gas clouds in the neighbourhood of a luminous active galactic nucleus (AGN). This creates a forbidden region for long-lived dusty clouds in the observed columnn density–Eddington fraction plane. (The Eddington fraction λEdd is the ratio of the bolometric luminosity of an AGN to the Eddington limit for its black hole mass.) The Swift/Burst Alert Telescope catalogue is the most complete hard X-ray selected sample of AGN and has 97 low-redshift AGN with measured column densities NH and inferred black hole masses. Eddington fractions for the sources have been obtained using recent bolometric corrections and the sources have been plotted on the NH–λEdd plane. Only one source lies in the forbidden region and it has a large value of NH due to an ionized warm absorber, for which radiation pressure is reduced. The effective Eddington limit for the source population indicates that the high column density clouds in the more luminous objects lie within the inner few pc, where the central black hole provides at least half the mass. Our result shows that radiation pressure does affect the presence of gas clouds in the inner galaxy bulge. We discuss briefly how the NH–λEdd plane may evolve to higher redshift, when feedback due to radiation pressure may have been strong.

IGR J16351-5806: another close by Compton-thick AGN

Abstract IGR J16351-5806 has been associated with the Seyfert 2 galaxy ESO 137-G34, having been first reported as a high energy emitter in the third INTEGRAL / Imager on Board the INTEGRAL Satellite survey. Using a new diagnostic tool based on X-ray column density measurements versus softness ratios (F2-10 keV/F20-100 keV), we have previously identified this source as a candidate Compton-thick active galactic nuclei (AGN). In the present work, we have analysed combined XMM–Newton and INTEGRAL data of IGR J16351-5806 in order to study its broad-band spectrum and investigate its Compton-thick nature. The prominent Kα fluorescence line around 6.4 keV (EW &amp;gt; 1 keV) together with a flat 2–10 keV spectrum immediately point to a highly obscured source. The overall spectrum can be interpreted in terms of a transmission scenario where some of the high energy radiation is able to penetrate through the thick absorption and be observed together with its reflection from the surface of the torus. A good fit is also obtained using a pure reflection spectrum; in this case, the primary continuum is totally depressed and only its reflection is observed. An alternative possibility is that of a complex absorption, where two layers of absorbing matter each partially covering the central nucleus are present in IGR J16351-5806. All three scenarios are compatible from a statistical viewpoint and provide reasonable AGN spectral parameters; more importantly all point to a source with an absorbing column greater than 1.5 × 1024 cm-2, that is to a Compton-thick AGN. Because of this heavy obscuration, some extra components which would otherwise be hidden are able to emerge at low energies and can be studied; a thermal component with kT in the range 0.6–0.7 keV and free metal abundance is statistically required in all three scenarios while a scattered power law is only present in the pure reflection model. By providing strong evidence for the Compton-thick nature of IGR J16351-5806, we indirectly confirm the validity of the Malizia et al. diagnostic diagram.

THE “TRUE” COLUMN DENSITY DISTRIBUTION IN STAR-FORMING MOLECULAR CLOUDS

We use the COMPLETE Survey's observations of the Perseus star-forming region to assess and intercompare three methods for measuring column density in molecular clouds: extinction mapping (NIR); thermal emission mapping (FIR); and mapping the intensity of CO isotopologues. The structures shown by all three tracers are morphologically similar, but important differences exist. Dust-based measures give similar, log-normal, distributions for the full Perseus region, once careful calibration corrections are made. We also compare dust- and gas-based column density distributions for physically-meaningful sub-regions of Perseus, and we find significant variations in the distributions for those regions. Even though we have used 12CO data to estimate excitation temperatures, and we have corrected for opacity, the 13CO maps seem unable to give column distributions that consistently resemble those from dust measures. We have edited out the effects of the shell around the B-star HD 278942. In that shell's interior and in the parts where it overlaps the molecular cloud, there appears to be a dearth of 13CO, likely due either to 13CO not yet having had time to form in this young structure, and/or destruction of 13CO in the molecular cloud. We conclude that the use of either dust or gas measures of column density without extreme attention to calibration and artifacts is more perilous than even experts might normally admit. And, the use of 13CO to trace total column density in detail, even after proper calibration, is unavoidably limited in utility due to threshold, depletion, and opacity effects. If one's main aim is to map column density, then dust extinction seems the best probe. Linear fits amongst column density tracers are given, quantifying the inherent uncertainties in using one tracer (when compared with others). [abridged]

Multiple flaring activity in the supergiant fast X-ray transient IGR J08408−4503 observed withSwift

IGR J08408‐4503 is a supergiant fast X‐ray transient discovered in 2006 with a confirmed association with a O8.5Ib(f) supergiant star, HD 74194. We report on the analysis of two outbursts caught by Swift/BAT on 2006 October 4 and 2008 July 5, and followed up at softer energies with Swift/XRT. The 2008 XRT light curve shows a multiple-peaked structure with an initial bright flare that reached a flux of � 10 9 erg cm 2 s 1 (2‐10 keV), followed by two equally bright flares within 75 ks. The spectral characteris tics of the flares differ dramatically, with most of the difference, as derived via time-resolved spectroscopy, being due to absorbing column variations. We observe a gradual decrease of the NH, derived with a fit using absorbed power law model, as time passes. We interpret these NH variations as due to an ionization effect produced by the first flare, resulting in a significant d ecrease in the measured column density towards the source. The durations of the flares, as we ll as the times of the outbursts suggest that the orbital period is �35 days, if the flaring activity is interpreted within the framework of the Sidoli et al. (2007) model with the outbursts triggered by the neutron star passage inside an equatorial wind inclined with respect to the orbital plane.

Plasma-chemical processes in microwave plasma-enhanced chemical vapor deposition reactors operating with C/H/Ar gas mixtures

Microwave (MW) plasma-enhanced chemical vapor deposition (PECVD) reactors are widely used for growing diamond films with grain sizes spanning the range from nanometers through microns to millimeters. This paper presents a detailed description of a two-dimensional model of the plasma-chemical activation, transport, and deposition processes occurring in MW activated H/C/Ar mixtures, focusing particularly on the following base conditions: 4.4%CH4/7%Ar/balance H2, pressure p=150 Torr, and input power P=1.5 kW. The model results are verified and compared with a range of complementary experimental data in the companion papers. These comparators include measured (by cavity ring down spectroscopy) C2(a), CH(X), and H(n=2) column densities and C2(a) rotational temperatures, and infrared (quantum cascade laser) measurements of C2H2 and CH4 column densities under a wide range of process conditions. The model allows identification of spatially distinct regions within the reactor that support net CH4→C2H2 and C2H2→CH4 conversions, and provide a detailed mechanistic picture of the plasma-chemical transformations occurring both in the hot plasma and in the outer regions. Semianalytical expressions for estimating relative concentrations of the various C1Hx species under typical MW PECVD conditions are presented, which support the consensus view regarding the dominant role of CH3 radicals in diamond growth under such conditions.