scholarly journals Recent Advances in the studies of Reaction Rates relevant to Interstellar Chemistry

1987 ◽  
Vol 120 ◽  
pp. 1-18
Author(s):  
Nigel G. Adams ◽  
David Smith
Keyword(s):  
Laboratory Data ◽  
Dissociative Recombination ◽  
Reaction Rates ◽  
Rate Coefficients ◽  
Current Status ◽  
Laboratory Measurements ◽  
Interstellar Molecules ◽  
Interstellar Clouds ◽  
Radiative Association ◽  
Molecular Synthesis

The current status of laboratory measurements of the rate coefficients for ionic reactions involved in interstellar molecular synthesis is discussed and the experimental techniques used to acquire such data are briefly described. Examples are given of laboratory data which are being obtained at temperatures close to those of interstellar clouds. Particular attention is given to the results of recent theoretical and experimental work which show that the rate coefficients for the binary reactions of ions with polar molecules at low temperatures are much larger than previously assumed. It is shown how these new developments in experiment and theory are reconciling the differences between predicted and observed abundances for some interstellar molecules. Also briefly discussed are: - the phenomenon of isotope exchange in ion/neutral reactions which explains the apparent enrichment of heavy isotopes in some interstellar molecules, the role of atoms in molecular synthesis, some studies of ion/neutral reactions pertaining to shocked regions of interstellar clouds, ternary association reactions and the analogous radiative association reactions, and recent new laboratory measurements of dissociative recombination coefficients. Finally, some guidance is offered in the proper choice of critical kinetic data for use in interstellar chemical modelling and some further requirements and likely future developments are mentioned.

scholarly journals Molecular Synthesis in Interstellar Clouds: the Radiative Association Reaction H + OH ↠ H2O + hv

1980 ◽  
Vol 87 ◽  
pp. 289-290
Author(s):  
D. Field ◽  
N. G. Adams ◽  
D. Smith
Keyword(s):  
Laboratory Data ◽  
Reaction Sequence ◽  
Interstellar Clouds ◽  
Radiative Association ◽  
General Importance ◽  
Association Reaction ◽  
Molecular Synthesis ◽  
Significant Mechanism ◽  
Recent Laboratory ◽  
Reaction Schemes

On the evidence of some recent laboratory data for the association reaction H + OH + He → H2O + He, and following previously proposed ion-neutral association reaction schemes, we tentatively suggest that the radiative association reaction of H and OH can be a significant mechanism for the production of H2O in interstellar clouds, when compared with the ion-neutral reaction sequence. The ‘H-atom + radical’ association process may be of some general importance in the production of other small molecules in interstellar clouds.

scholarly journals Microwave Spectroscopy of Astrophysical Molecules

1989 ◽  
Vol 8 ◽  
pp. 339-344
Author(s):  
William M. Irvine
Keyword(s):  
Chemical Elements ◽  
Laboratory Data ◽  
Isotopic Fractionation ◽  
Reaction Rates ◽  
Branching Ratios ◽  
Microwave Spectroscopy ◽  
Interstellar Molecules ◽  
Interstellar Clouds ◽  
New Information ◽  
Astrophysical Molecules

ABSTRACTRecent detections of new molecules in dense interstellar clouds, first detections of certain chemical elements in interstellar molecules, and new information on isotopic fractionation of hydrogen in the interstellar medium are discussed in the context of the need for new laboratory data on transition rest frequencies, reaction rates, and branching ratios.

scholarly journals The Formation of Interstellar Molecules via Radiative Association Reactions

1980 ◽  
Vol 87 ◽  
pp. 323-324
Author(s):  
David Smith ◽  
Nigel G. Adams
Keyword(s):  
Rate Coefficients ◽  
Rate Data ◽  
Association Rate ◽  
Interstellar Molecules ◽  
Ion Molecule Reactions ◽  
Radiative Association ◽  
Temperature Dependences ◽  
Association Reaction

The radiative association rate coefficients and their temperature dependences have been estimated for several likely interstellar ion-molecule reactions from laboratory collisional association rate data. They include the CH3+ + H2 and CH3+ + H2O reactions, which we suggest lead to CH4 and CH3OH respectively, and the critical association reaction C+ + H2.

scholarly journals Effects of Nonthermal Internal Energy on Postshock Oxygen Chemistry

1987 ◽  
Vol 120 ◽  
pp. 295-296
Author(s):  
M. M. Graff ◽  
A. Dalgarno ◽  
A. F. Wagner
Keyword(s):  
Fine Structure ◽  
Internal Energy ◽  
Reaction Rates ◽  
Rate Coefficients ◽  
Shock Model ◽  
Energy Distributions ◽  
Interstellar Clouds ◽  
Thermal Measurements ◽  
Simple Extrapolation

The internal energy distributions of reactants in shocked interstellar clouds are discussed. Rate coefficients appropriate for the oxygen chemistry of shocks differ significantly from those deduced by simple extrapolation of thermal measurements. A one-fluid MHD shock model examines nonthermal effects for a 10 km s−1 shock propagating through clouds of initial densities of 10 and 105 cm−3, using oxygen-hydrogen reaction rates that are specific to the vibrational, rotational, and fine structure temperatures of the reactants.

Formation and destruction of molecular ions in interstellar clouds

1988 ◽  
Vol 324 (1578) ◽  
pp. 257-273 ◽  
Keyword(s):  
Dissociative Recombination ◽  
Cosmic Ray ◽  
Spectroscopic Studies ◽  
Molecular Ions ◽  
Interstellar Chemistry ◽  
Interstellar Clouds ◽  
Polyatomic Ions ◽  
Positive Ions ◽  
Radiative Association ◽  
Reaction Processes

A brief review is given of the role of molecular positive ions in interstellar chemistry. It is indicated how the simplest ions, which are formed by photoionization and cosmic-ray ionization, are converted to polyatomic ions by sequential gas-phase ionic reaction processes such as proton transfer, carbon insertion and radiative association. The importance of H3 and CH3 ions in the initial stages of molecular synthesis and the analogous roles of H2D+ and CH2D+ (which are formed in the reactions of H3 and CHg with HD) in the production of deuterated molecules are stressed. Recent work is also mentioned concerning the possible routes to c-C3H2 the first cyclic molecule to be detected in interstellar clouds. The process of dissociative recombination of positive ions with electrons is also discussed, because it is commonly invoked as the final step in the destruction of polyatomic ions and in the formation of many of the observed neutral molecules in interstellar clouds, even though the products of such reactions are currently a matter for speculation. It is stressed how spectroscopic studies of the structures and the products of reactions of molecular ions can further advance understanding in the field of interstellar chemistry.

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