The interstellar gas-phase chemistry of HCN and HNC

Abstract

We review the reactions involving HCN and HNC in dark molecular clouds to elucidate new chemical sources and sinks of these isomers. We find that the most important reactions for the HCN-HNC system are Dissociative Recombination (DR) reactions of HCNH+ (HCNH+ + e-), the ionic CN + H3+, HCN + C+, HCN and HNC reactions with H+/He+/H3+/H3O+/HCO+, the N + CH2 reaction and two new reactions: H + CCN and C + HNC. We test the effect of the new rate constants and branching ratios on the predictions of gas-grain chemical models for dark cloud conditions. The rapid C + HNC reaction keeps the HCN/HNC ratio significantly above one as long as the carbon atom abundance remains high. However, the reaction of HCN with H3+ followed by DR of HCNH+ acts to isomerize HCN into HNC when carbon atoms and CO are depleted leading to a HCN/HNC ratio close to or slightly greater than 1. This agrees well with observations in TMC-1 and L134N taking into consideration the overestimation of HNC abundances through the use of the same rotational excitation rate constants for HNC as for HCN in many radiative transfer models.

arXiv commentAccepted for publication in MNRAS

References in corpus (17)

• A KInetic Database for Astrochemistry (KIDA)
• Non-thermal desorption from interstellar dust grains via exothermic surface reactions
• Does IRAS 16293-2422 have a hot core? Chemical inventory and abundance changes in its protostellar environment
• Molecular Inventories and Chemical Evolution of Low-mass Protostellar Envelopes
• Reaction Networks For Interstellar Chemical Modelling: Improvements and Challenges
• Chemistry in Disks. IV. Benchmarking gas-grain chemical models with surface reactions
• Oxygen depletion in dense molecular clouds: a clue to a low O2 abundance?
• Comparative Chemistry of Diffuse Clouds II: CN, HCN, HNC, CH3CN & N2H+
• Nitrogen chemistry and depletion in starless cores
• Molecular absorption lines toward star-forming regions : a comparative study of HCO+, HNC, HCN, and CN
• Cold CO in circumstellar disks: On the effects of photodesorption and vertical mixing
• The gas-phase chemistry of carbon chains in dark cloud chemical models
• The Transition from Atomic to Molecular Hydrogen in Interstellar Clouds: 21cm Signature of the Evolution of Cold Atomic Hydrogen in Dense Clouds
• Chemical Modelling of Young Stellar Objects, I. Method and Benchmarks
• Multidimensional chemical modelling, II. Irradiated outflow walls
• HCN and HNC mapping of the protostellar core Cha-MMS1
• Low temperature rate constants for the N(4S) + CH(X2Πr) reaction. Implications for N2 formation cycles in dense interstellar clouds

Cited by in corpus (62)

• The 2014 KIDA network for interstellar chemistry
• Gas and grain chemical composition in cold cores as predicted by the Nautilus 3-phase model
• Modeling Complex Organic Molecules in dense regions: Eley-Rideal and complex induced reaction
• Isotopic fractionation of carbon, deuterium and nitrogen : a full chemical study
• The genealogical tree of ethanol: gas-phase formation of glycolaldehyde, acetic acid and formic acid
• Gas phase Elemental abundances in Molecular cloudS (GEMS) I. The prototypical dark cloud TMC 1
• The interstellar chemistry of C3H and C3H2 isomers
• Chemistry in Protoplanetary Disks: the gas-phase CO/H2 ratio and the Carbon reservoir
• CN rings in full protoplanetary disks around young stars as probes of disk structure
• Nitrogen isotope fractionation in protoplanetary disks
• Spin-state chemistry of deuterated ammonia
• Gas phase Elemental abundances in Molecular cloudS (GEMS). IV. Observational results and statistical trends
• Nitrogen and hydrogen fractionation in high-mass star forming cores from observations of HCN and HNC
• Detection of Interstellar HC${}_4$NC and an Investigation of Isocyanopolyyne Chemistry under TMC-1 Conditions
• Chemical and physical characterization of collapsing low-mass prestellar dense cores
• Detection of the HC${}_3$NH${}^{+}$ and HCNH${}^{+}$ ions in the L1544 pre-stellar core
• The C(3P) + NH3 reaction in interstellar chemistry: II. Low temperature rate constants and modeling of NH, NH2 and NH3 abundances in dense interstellar clouds
• Depletion of heavy nitrogen in the cold gas of star-forming regions
• Seeds of Life in Space (SOLIS). X. Interstellar Complex Organic Molecules in the NGC 1333 IRAS 4A outflows
• The C(3P) + NH3 reaction in interstellar chemistry: I. Investigation of the product formation channels
• The role of C/O in nitrile astrochemistry in PDRs and planet-forming disks
• A cold accretion flow onto one component of a multiple protostellar system
• Space and laboratory observation of the deuterated cyanomethyl radical HDCCN
• Chemical nitrogen fractionation in dense molecular clouds
• Establishing the evolutionary timescales of the massive star formation process through chemistry
• MOVES IV. Modelling the influence of stellar XUV-flux, cosmic rays, and stellar energetic particles on the atmospheric composition of the hot Jupiter HD 189733b
• The ALMA Lupus protoplanetary disk survey: evidence for compact gas disks and molecular rings from CN
• Nobeyama 45-m mapping observations toward nearby molecular clouds, Orion A, Aquila Rift, and M17: Project overview
• Discovery of thiofulminic acid with the QUIJOTE line survey: A study of the isomers of HNCS and HNCO in TMC-1
• Chemistry of TMC-1 with multiply deuterated species and spin chemistry of H2, H2+, H3+ and their isotopologues
• An Expanded Gas-Grain Model for Interstellar Glycine
• Exploring molecular complexity with ALMA (EMoCA): Complex isocyanides in Sgr B2(N)
• A proposed chemical scheme for HCCO formation in cold dense clouds
• Molecular Polymorphism: Microwave Spectra, Equilibrium Structures, and an Astronomical Investigation of the HNCS Isomeric Family
• The GRETOBAPE gas-phase reaction network: the importance of being exothermic
• A view of Large Magellanic Cloud HII regions N159, N132, and N166 through the 345 GHz window
• Discovery of interstellar 3-cyano propargyl radical, CH2CCCN
• HCN emission from translucent gas and UV-illuminated cloud edges revealed by wide-field IRAM 30m maps of Orion B GMC: Revisiting its role as tracer of the dense gas reservoir for star formation
• Exploring HNC and HCN line emission as probes of the protoplanetary disk temperature
• Laboratory and astronomical discovery of the cyanovinyl radical H2CCCN
• The First Mid-Infrared Detection of HNC in the Interstellar Medium: Probing the Extreme Environment Towards the Orion Hot Core
• Tracing the atomic nitrogen abundance in star-forming regions with ammonia deuteration
• Modelling the Molecular Gas in NGC 6240
• Linking the dust and chemical evolution: Taurus and Perseus -- New collisional rates for HCN, HNC, and their C, N, and H isotopologues
• First survey of HCNH${}^{+}$ in high-mass star-forming cloud cores
• Planck Cold Clumps in the lambda Orionis Complex. III. A chemical probe of stellar feedback on cores in the lambda Orionis cloud
• A correlation between chemistry, polarization and dust properties in the Pipe Nebula starless core FeSt 1-457
• Nobeyama 45-m Mapping Observations toward Orion A. III. Multi-Line Observations toward an Outflow-shocked Region, OMC-2 FIR
• Chemical compositions of five Planck cold clumps
• G331.512-0.103: An Interstellar Laboratory for Molecular Synthesis I. The Ortho-to-para Ratios for CH${}_3$OH and CH${}_3$CN
• Measurements of rate coefficients of CN${}^{+}$, HCN${}^{+}$ and HNC${}^{+}$ collisions with H${}_2$ at cryogenic temperatures
• Cyano radical emission at small spatial scales towards massive protostars
• Chemical modeling of internal photon-dominated regions surrounding deeply embedded HC/UCHII regions
• H2CN/H2NC abundance ratio: a new potential temperature tracer for the interstellar medium
• Protonated hydrogen cyanide as a tracer of pristine molecular gas
• High Resolution Overtone Spectroscopy of HNC${}^{+}$ and HCN${}^{+}$
• What did the seahorse swallow? APEX 170 GHz observations of the chemical conditions in the Seahorse infrared dark cloud
• Rovibrational Overtone and Combination Bands of the HCNH+ Ion
• Laboratory Rotational Spectra of Silyl Isocyanide
• Formation of HNC and HCN isomers in molecular plasmas revealed by frequency comb and quantum cascade laser spectroscopy
• Carbon chain diversity in L1544 and IRAS 16293-2422: an astrochemical pathfinder study for the SKAO
• First Detection of HC5N in a Class II Disk around TW Hya