Gas-phase chemistry in dense interstellar clouds including grain surface molecular depletion and desorption

1995 ◽  
Vol 441 ◽  
pp. 222 ◽  
Author(s):  
E. A. Bergin ◽  
W. D. Langer ◽  
P. F. Goldsmith
Keyword(s):  
Gas Phase ◽  
Interstellar Clouds ◽  
Gas Phase Chemistry ◽  
Phase Chemistry ◽  
Grain Surface

scholarly journals Molecular Formation in Hot Diffuse Clouds

1980 ◽  
Vol 87 ◽  
pp. 273-280
Author(s):  
A. Dalgarno
Keyword(s):  
Gas Phase ◽  
Interstellar Clouds ◽  
Gas Phase Chemistry ◽  
Molecular Formation ◽  
Phase Chemistry ◽  
Diffuse Clouds

A description is given of the processes of molecular formation and destruction in diffuse interstellar clouds and detailed models of the clouds lying towards ζ Ophiuchi, ζ Persei and o Persei are used to assess the validity of gas phase chemistry. Modifications that may arise from shock-heated regions are discussed.

scholarly journals Depletion of 15N in the center of L1544: Early transition from atomic to molecular nitrogen?

2018 ◽  
Vol 615 ◽  
pp. L16 ◽  
Author(s):  
K. Furuya ◽  
Y. Watanabe ◽  
T. Sakai ◽  
Y. Aikawa ◽  
S. Yamamoto
Keyword(s):  
Gas Phase ◽  
Molecular Nitrogen ◽  
Abundance Ratio ◽  
Elemental Abundance ◽  
Evolutionary Stage ◽  
Gas Phase Chemistry ◽  
Far Ultraviolet ◽  
Phase Chemistry ◽  
Grain Surface

We performed sensitive observations of the N15ND+(1–0) and 15NND+(1–0) lines toward the prestellar core L1544 using the IRAM 30 m telescope. The lines are not detected down to 3σ levels in 0.2 km s−1 channels of ~6 mK. The non-detection provides the lower limit of the 14N/15N ratio for N2D+ of ~700–800, which is much higher than the elemental abundance ratio in the local interstellar medium of ~200–300. The result indicates that N2 is depleted in 15N in the central part of L1544, because N2D+ preferentially traces the cold dense gas, and because it is a daughter molecule of N2. In situ chemistry is probably not responsible for the 15N depletion in N2; neither low-temperature gas phase chemistry nor isotope selective photodissociation of N2 explains the 15N depletion; the former prefers transferring 15N to N2, while the latter requires the penetration of interstellar far-ultraviolet (FUV) photons into the core center. The most likely explanation is that 15N is preferentially partitioned into ices compared to 14N via the combination of isotope selective photodissociation of N2 and grain surface chemistry in the parent cloud of L1544 or in the outer regions of L1544, which are not fully shielded from the interstellar FUV radiation. The mechanism is most efficient at the chemical transition from atomic to molecular nitrogen. In other words, our result suggests that the gas in the central part of L1544 has previously gone trough the transition from atomic to molecular nitrogen in the earlier evolutionary stage, and that N2 is currently the primary form of gas-phase nitrogen.

scholarly journals The Effect of an Inert Solid Reservoir on Molecular Abundances in Dense Interstellar Clouds

2012 ◽  
Vol 21 (4) ◽  
Author(s):  
Juris Kalvāns ◽  
Ivar Shmeld
Keyword(s):  
Gas Phase ◽  
Reference Model ◽  
Solid Phase ◽  
Chemical Species ◽  
Interstellar Gas ◽  
Interstellar Clouds ◽  
Major Chemical ◽  
Molecular Abundances ◽  
Phase Chemistry ◽  
Grain Surface

AbstractThe question, what is the role of freeze-out of chemical species in determining the molecular abundances in the interstellar gas is a matter of debate. We investigate a theoretical case of a dense interstellar molecular cloud core by time-dependent modeling of chemical kinetics, where grain surface reactions deliberately are not included. That means, the gas-phase and solid-phase abundances are influenced only by gas reactions, accretion on grains and desorption. We compare the results to a reference model where no accretion occurs, and only gas-phase reactions are included. We can trace that the purely physical processes of molecule accretion and desorption have major chemical consequences on the gas-phase chemistry. The main effect of introduction of the gas-grain interaction is long-term molecule abundance changes that come nowhere near an equilibrium during the typical lifetime of a prestellar core.

scholarly journals Detection of Deuterated Formaldehyde in Interstellar Clouds

1980 ◽  
Vol 87 ◽  
pp. 439-443
Author(s):  
William D. Langer ◽  
Margaret A. Frerking ◽  
Richard A. Linke ◽  
Robert W. Wilson
Keyword(s):  
Gas Phase ◽  
Interstellar Clouds ◽  
Gas Phase Chemistry ◽  
Phase Chemistry ◽  
First Time

AbstractDeuterated formaldehyde has been detected for the first time in interstellar clouds; the observed ratio HDCO/H2CO implies formation by gas phase chemistry.

scholarly journals What Species Remain to be Seen?

1992 ◽  
Vol 150 ◽  
pp. 181-186 ◽  
Author(s):  
B. E. Turner
Keyword(s):  
Gas Phase ◽  
Refractory Element ◽  
Circumstellar Envelopes ◽  
Neutral Species ◽  
Interstellar Clouds ◽  
Gas Phase Chemistry ◽  
Element Chemistry ◽  
Thermochemical Equilibrium ◽  
Phase Chemistry ◽  
Laboratory Synthesis

We review what species remain to be seen for several types of astrochemistry: Thermochemical Equilibrium (TE) in circumstellar envelopes (CSEs); photo- and ion-molecule chemistry in CSEs; ion-molecule chemistry in cold interstellar clouds; grain chemistry (passive, catalytic, disruptive); and shock chemistry. In CSEs, a rich Si gas-phase chemistry is now recognized, and two predicted species (SiN, SiH2) have been seen. Others are predicted. In the ISM, a global picture of refractory-element chemistry predicts that compounds of Mg, Na, Fe, and possibly Al occur with detectable gas-phase abundance. Predicted species require laboratory synthesis and spectroscopy. Reactions of hydrocarbon ions with neutral species dominate the formation of the families CnH, HCnN, H2Cn, and CnO in both interstellar (TMC-1) and circumstellar (IRC10216) cases, and readily explain the favored values of n in each case as well as predicting which higher-n species remain to be seen. Confirmation of H3O+ (interstellar) is discussed.

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