scholarly journals The water line emission and ortho-to-para ratio in the Orion Bar photon-dominated region

2019 ◽  
Vol 632 ◽  
pp. A8 ◽  
Author(s):  
T. Putaud ◽  
X. Michaut ◽  
F. Le Petit ◽  
E. Roueff ◽  
D. C. Lis
Keyword(s):  
Gas Phase ◽  
Thermal Equilibrium ◽  
Line Emission ◽  
Water Molecules ◽  
Kinetic Temperature ◽  
Spin Temperature ◽  
Interstellar Gas ◽  
Water Abundance ◽  
Fractional Abundance ◽  
Phase Water

Context. The ortho-to-para ratio (OPR) of water in the interstellar medium (ISM) is often assumed to be related to the formation temperature of water molecules, making it a potentially interesting tracer of the thermal history of interstellar gas. Aims. A very low OPR of 0.1–0.5 was previously reported in the Orion Bar photon-dominated region (PDR), based on observations of two optically thin H218O lines which were analyzed by using a single-slab large velocity gradient (LVG) model. The corresponding spin temperature does not coincide with the kinetic temperature of the molecular gas in this UV-illuminated region. This was interpreted as an indication of water molecules being formed on cold icy grains which were subsequently released by UV photodesorption. Methods. A more complete set of water observations in the Orion Bar, including seven H216O lines and one H218O line, carried out using Herschel/HIFI instrument, was reanalyzed using the Meudon PDR code to derive gas-phase water abundance and the OPR. The model takes into account the steep density and temperature gradients present in the region. Results. The model line intensities are in good agreement with the observations assuming that water molecules formed with an OPR corresponding to thermal equilibrium conditions at the local kinetic temperature of the gas and when solely considering gas-phase chemistry and water gas-grain exchanges through adsorption and desorption. Gas-phase water is predicted to arise from a region deep into the cloud, corresponding to a visual extinction of AV ~ 9, with a H216O fractional abundance of ~2 × 10−7 and column density of (1.4 ± 0.8) × 1015 cm−2 for a total cloud depth of AV = 15. A line-of-sight average OPR of 2.8 ± 0.2 is derived. Conclusions. The observational data are consistent with a nuclear spin isomer repartition corresponding to the thermal equilibrium at a temperature of 36 ± 2 K, much higher than the spin temperature previously reported for this region and close to the gas kinetic temperature in the water-emitting gas.

A Comparative Study of the BJH- and MCYL-Type Potentials Applied to the Gaseous Water Dimer

1991 ◽  
Vol 46 (5) ◽  
pp. 426-432
Author(s):  
Zdenek Slanina
Keyword(s):  
Gas Phase ◽  
Minimum Energy ◽  
Water Dimer ◽  
Energy Structure ◽  
Water Molecules ◽  
Constant Matrix ◽  
Force Constant Matrix ◽  
Molecular Force ◽  
Phase Water ◽  
Derivatives Of

AbstractVarious refined potentials describing the intra- and inter-molecular force fields of water molecules arc used to calculate the properties of the gas-phase water dimer. The intra-molecular parts have been taken from spectroscopic or quantum-chemical sources. The minimum energy structure was found iteratively using the first derivatives of the potential; the force-constant matrix was constructed by numerical difierentation. A quite close agreement between the Bopp-Jancso-Heinzinger and the Matsuoka-Clementi-Yoshimine-Lie potentials is found. The treatment is applied to seven observed water-dimer isotopomeric isomerizations

scholarly journals Low temperature rates for key steps of interstellar gas-phase water formation

2018 ◽  
Vol 4 (6) ◽  
pp. eaar3417 ◽  
Author(s):  
Sunil S. Kumar ◽  
Florian Grussie ◽  
Yury V. Suleimanov ◽  
Hua Guo ◽  
Holger Kreckel
Keyword(s):  
Low Temperature ◽  
Gas Phase ◽  
Interstellar Gas ◽  
Water Formation ◽  
Phase Water ◽  
Key Steps

Nuclear dynamics and spectator effects in resonant inelastic soft x-ray scattering of gas-phase water molecules

2012 ◽  
Vol 136 (14) ◽  
pp. 144311 ◽  
Author(s):  
Lothar Weinhardt ◽  
Andreas Benkert ◽  
Frank Meyer ◽  
Monika Blum ◽  
Regan G. Wilks ◽  
...  
Keyword(s):  
Gas Phase ◽  
Water Molecules ◽  
Nuclear Dynamics ◽  
X Ray ◽  
X Ray Scattering ◽  
Phase Water ◽  
Ray Scattering

scholarly journals Seeds of Life in Space (SOLIS)

2020 ◽  
Vol 635 ◽  
pp. A17 ◽  
Author(s):  
C. Codella ◽  
C. Ceccarelli ◽  
E. Bianchi ◽  
N. Balucani ◽  
L. Podio ◽  
...  
Keyword(s):  
Spatial Distribution ◽  
Gas Phase ◽  
Interstellar Dust ◽  
Line Emission ◽  
Abundance Ratio ◽  
Kinetic Temperature ◽  
Set Constraints ◽  
Ethyl Radical ◽  
Model Predictions ◽  
Upper Level

Context. It is nowadays clear that a rich organic chemistry takes place in protostellar regions. However, the processes responsible for it, that is, the dominant formation routes to interstellar complex organic molecules, are still a source of debate. Two paradigms have been evoked: the formation of these molecules on interstellar dust mantles and their formation in the gas phase from simpler species previously synthesised on the dust mantles. Aims. In the past, observations of protostellar shocks have been used to set constraints on the formation route of formamide (NH2CHO), exploiting its observed spatial distribution and comparison with astrochemical model predictions. In this work, we follow the same strategy to study the case of acetaldehyde (CH3CHO). Methods. To this end, we used the data obtained with the IRAM-NOEMA interferometer in the framework of the Large Program SOLIS to image the B0 and B1 shocks along the L1157 blueshifted outflow in methanol (CH3OH) and acetaldehyde line emission. Results. We imaged six CH3OH and eight CH3CHO lines which cover upper-level energies up to ~30 K. Both species trace the B0 molecular cavity as well as the northern B1 portion, that is, the regions where the youngest shocks (~1000 yr) occurred. The CH3OH and CH3CHO emission peaks towards the B1b clump, where we measured the following column densities and relative abundances: 1.3 × 1016 cm−2 and 6.5 × 10−6 (methanol), and 7 × 1013 cm−2 and 3.5 × 10−8 (acetaldehyde). We carried out a non-LTE (non-Local Thermodinamic Equilibrium) Large Velocity Gradient (LVG) analysis of the observed CH3OH line: the average kinetic temperature and density of the emitting gas are Tkin ~ 90 K and nH2 ~ 4 × 105 cm−3, respectively. The CH3OH and CH3CHO abundance ratio towards B1b is 190, varying by less than a factor three throughout the whole B0–B1 structure. Conclusions. Comparison of astrochemical model predictions with the observed methanol and acetaldehyde spatial distribution does not allow us to distinguish whether acetaldehyde is formed on the grain mantles or in the gas phase, as its gas-phase formation, which is dominated by the reaction of ethyl radical (CH3CH2) with atomic oxygen, is very fast. Observations of acetaldehyde in younger shocks, for example those of ~102 yr old, and/or of the ethyl radical, whose frequencies are not presently available, are necessary to settle the issue.

The interstellar gas-phase formation of CO2 – Assisted or not by water molecules?

2006 ◽  
Vol 320 (2-3) ◽  
pp. 214-228 ◽  
Author(s):  
D. Talbi ◽  
G.S. Chandler ◽  
A.L. Rohl
Keyword(s):  
Gas Phase ◽  
Phase Formation ◽  
Water Molecules ◽  
Interstellar Gas

scholarly journals Molecular gas in the Herschel-selected strongly lensed submillimeter galaxies at z ~ 2–4 as probed by multi-J CO lines

2017 ◽  
Vol 608 ◽  
pp. A144 ◽  
Author(s):  
C. Yang ◽  
A. Omont ◽  
A. Beelen ◽  
Y. Gao ◽  
P. van der Werf ◽  
...  
Keyword(s):  
Star Formation ◽  
High Redshift ◽  
Line Emission ◽  
Far Infrared ◽  
Molecular Gas ◽  
Kinetic Temperature ◽  
Large Area ◽  
Line Energy ◽  
Submillimeter Galaxies ◽  
Dust Mass

We present the IRAM-30 m observations of multiple-J CO (Jup mostly from 3 up to 8) and [C I](3P2 → 3P1) ([C I](2–1) hereafter) line emission in a sample of redshift ~2–4 submillimeter galaxies (SMGs). These SMGs are selected among the brightest-lensed galaxies discovered in the Herschel-Astrophysical Terahertz Large Area Survey (H-ATLAS). Forty-seven CO lines and 7 [C I](2–1) lines have been detected in 15 lensed SMGs. A non-negligible effect of differential lensing is found for the CO emission lines, which could have caused significant underestimations of the linewidths, and hence of the dynamical masses. The CO spectral line energy distributions (SLEDs), peaking around Jup ~ 5–7, are found to be similar to those of the local starburst-dominated ultra-luminous infrared galaxies and of the previously studied SMGs. After correcting for lensing amplification, we derived the global properties of the bulk of molecular gas in the SMGs using non-LTE radiative transfer modelling, such as the molecular gas density nH2 ~ 102.5–104.1 cm-3 and the kinetic temperature Tk  ~ 20–750 K. The gas thermal pressure Pth ranging from~105 K cm-3 to 106 K cm-3 is found to be correlated with star formation efficiency. Further decomposing the CO SLEDs into two excitation components, we find a low-excitation component with nH2 ~ 102.8–104.6 cm-3 and Tk  ~ 20–30 K, which is less correlated with star formation, and a high-excitation one (nH2 ~ 102.7–104.2 cm-3, Tk  ~ 60–400 K) which is tightly related to the on-going star-forming activity. Additionally, tight linear correlations between the far-infrared and CO line luminosities have been confirmed for the Jup ≥ 5 CO lines of these SMGs, implying that these CO lines are good tracers of star formation. The [C I](2–1) lines follow the tight linear correlation between the luminosities of the [C I](2–1) and the CO(1–0) line found in local starbursts, indicating that [C I] lines could serve as good total molecular gas mass tracers for high-redshift SMGs as well. The total mass of the molecular gas reservoir, (1–30) × 1010M⊙, derived based on the CO(3–2) fluxes and αCO(1–0) = 0.8 M⊙ ( K km s-1 pc2)-1, suggests a typical molecular gas depletion time tdep ~ 20–100 Myr and a gas to dust mass ratio δGDR ~ 30–100 with ~20%–60% uncertainty for the SMGs. The ratio between CO line luminosity and the dust mass L′CO/Mdust appears to be slowly increasing with redshift for high-redshift SMGs, which need to be further confirmed by a more complete SMG sample at various redshifts. Finally, through comparing the linewidth of CO and H2O lines, we find that they agree well in almost all our SMGs, confirming that the emitting regions of the CO and H2O lines are co-spatially located.

Rate coefficients for interstellar gas-phase chemistry

1993 ◽  
Vol 89 (13) ◽  
pp. 2193 ◽  
Author(s):  
Bertrand R. Rowe ◽  
Andr� Canosa ◽  
Ian R. Sims
Keyword(s):  
Gas Phase ◽  
Rate Coefficients ◽  
Interstellar Gas ◽  
Gas Phase Chemistry ◽  
Phase Chemistry

scholarly journals Computational Evidence Suggests That 1-chloroethanol May Be an Intermediate in the Thermal Decomposition of 2-chloroethanol into Acetaldehyde and HCl

2019 ◽  
Author(s):  
Zoi Salta ◽  
Agnie M. Kosmas ◽  
Oscar Ventura ◽  
Vincenzo Barone
Keyword(s):  
Aqueous Solution ◽  
Water Molecule ◽  
Gas Phase ◽  
Density Functional ◽  
Water Molecules ◽  
Functional Theory ◽  
Direct Transformation ◽  
The Density Functional Theory ◽  
Successive Step ◽  
The One

<p>The dehalogenation of 2-chloroethanol (2ClEtOH) in gas phase with and without participation of catalytic water molecules has been investigated using methods rooted into the density functional theory. The well-known HCl elimination leading to vinyl alcohol (VA) was compared to the alternative elimination route towards oxirane and shown to be kinetically and thermodynamically more favorable. However, the isomerization of VA to acetaldehyde in the gas phase, in the absence of water, was shown to be kinetically and thermodynamically less favorable than the recombination of VA and HCl to form the isomeric 1-chloroethanol (1ClEtOH) species. This species is more stable than 2ClEtOH by about 6 kcal mol<sup>-1</sup>, and the reaction barrier is 22 kcal mol<sup>-1</sup> vs 55 kcal mol<sup>-1</sup> for the direct transformation of VA to acetaldehyde. In a successive step, 1ClEtOH can decompose directly to acetaldehyde and HCl with a lower barrier (29 kcal mol<sup>-1</sup>) than that of VA to the same products (55 kcal mol<sup>-1</sup>). The calculations were repeated using a single ancillary water molecule (W) in the complexes 2ClEtOH_W and 1ClEtOH_W. The latter adduct is now more stable than 2ClEtOH_W by about 8 kcal mol<sup>-1</sup>, implying that the water molecule increased the already higher stability of 1ClEtOH in the gas phase. However, this catalytic water molecule lowers dramatically the barrier for the interconversion of VA to acetaldehyde (from 55 to 6 kcal mol<sup>-1</sup>). This barrier is now smaller than the one for the conversion to 1ClEtOH (which also decreases, but not so much, from 22 to 12 kcal mol<sup>-1</sup>). Thus, it is concluded that while 1ClEtOH may be a plausible intermediate in the gas phase dehalogenation of 2ClEtOH, it is unlikely that it plays a major role in water complexes (or, by inference, aqueous solution). It is also shown that neither in the gas phase nor in the cluster with one water molecule, the oxirane path is competitive with the VA alcohol path.</p>

Solvation of propanediol ions by water molecules in the gas phase

2004 ◽  
Vol 15 (8) ◽  
pp. 1123-1127 ◽  
Author(s):  
John J. Gilligan ◽  
Nancy E. Vieira ◽  
Alfred L. Yergey
Keyword(s):  
Gas Phase ◽  
Water Molecules
Sign in / Sign up

Export Citation Format

Share Document