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Imidogen is an inorganic compound with the chemical formula NH.[2] Like other simple radicals, it is highly reactive and consequently short-lived except as a dilute gas. Its behavior depends on its spin multiplicity, i.e. the triplet vs singlet ground state.

Imidogen
Space-filling model of the imidogen radical
Names
IUPAC name
λ1-Azanylidene[1]
Other names
Aminylene

Azanylene
Azanylidene
Imidogen
Nitrene

λ1-azane
hydridonitrogen
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
66
Properties
HN
Molar mass 15.02 g·mol−1
Structure
linear
Thermochemistry
21.19 J K−1 mol−1
181.22 kJ K−1 mol−1
358.43 kJ mol−1
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Contents

Production and propertiesEdit

Imidogen can be generated by electrical discharge in an atmosphere of ammonia.[3]

Imidogen has a large rotational splitting and a weak spin-spin interaction, therefore it will be less likely to undergo collision-induced Zeeman transitions.[3] Ground-state imidogen can be magnetically trapped using buffer-gas loading from a molecular beam.[3]

The first excited state (a1Δ) has a long lifetime its relaxation to ground state (X3Σ) is spin-forbidden.[4][5] Imidogen undergoes collision-induced intersystem crossing.[6]

ReactivityEdit

Imidogen is isoelectronic with carbene (CH2) and oxygen (O) atoms, and it exhibits comparable reactivity.[4] The first excited state can be detected by laser-induced fluorescence (LIF).[4] LIF methods allow for detection of depletion, production, and chemical products of NH. It reacts with nitric oxide (NO):

NH + NO → N2 + OH
NH + NO → N2O + H

The former reaction is more favorable with a ΔH0 of −408 ± 2 kJ/mol compared to a ΔH0 of −147 ± 2 kJ/mol for the latter reaction.[7]

NomenclatureEdit

The trivial name nitrene is the preferred IUPAC name. The systematic names, λ1-azane and hydridonitrogen, valid IUPAC names, are constructed according to the substitutive and additive nomenclatures, respectively.

In appropriate contexts, imidogen can be viewed as ammonia with two hydrogen atoms removed, and as such, azylidene may be used as a context-specific systematic name, according to substitutive nomenclature. By default, this name pays no regard to the radicality of the imidogen molecule. Although, in even more specific context, it can also name the non-radical state, whereas the diradical state is named azanediyl.

AstrochemistryEdit

Interstellar NH was identified in the diffuse clouds toward Zeta Persei and HD 27778 from high-resolution high S/N spectra of the NH Å 3Pi-X 3Sigma (0,0) absorption band near 3358 Å.[8]A temperature of about 30 K favored an efficient production of CN from NH within the diffuse cloud.[9][10][8]

Reactions relevant to astrochemistryEdit

Chemical reactions[11][12][13]
Reaction Rate Constant Rate/[H2]2
N + H → NH + e 1x10−9 3.5x10−18
NH2 + O → NH + OH 2.546x10−13 1.4x10−13
NH2+ + e → NH + H 3.976x10−7 2.19x10−21
NH3+ + e → NH + H + H 8.49x10−7 2.89x10−19
NH + N → N2 + H 4.98x10−11 4.36x10−16
NH + O → OH + N 1.16x10−11 1.54x10−14
NH + C+ → CN+ + H 7.8x10−10 4.9x10−19
NH + H3+ → NH2+ + H2 1.3x10−9 3.18x10−19
NH + H+ → NH+ + H 2.1x10−9 4.05x10−20

Within diffuse clouds H + N → NH + e is a major formation mechanism. Near chemical equilibrium important NH formation mechanisms are recombinations of NH2+ and NH3+ ions with electrons. Depending on the radiation field in the diffuse cloud, NH2 can also contribute.

NH is destroyed in diffuse clouds by photodissociation and photoionization. In dense clouds NH is destroyed by reactions with atomic oxygen and nitrogen. O+ and N+ form OH and NH in diffuse clouds. NH is involved in creating N2, OH, H, CN+, CH, N, NH2+,NH+ for the interstellar medium.

NH has been reported in the diffuse interstellar medium but not in dense molecular clouds.[14] The purpose of detecting NH is often to get a better estimate of the rotational constants and vibrational levels of NH.[15] It is also needed in order to confirm theoretical data which predicts N and NH abundances in stars which produce N and NH and other stars with left over trace amounts of N and NH.[16] Using current values for rotational constants and vibrations of NH as well as those of OH and CH permit studying the carbon, nitrogen and oxygen abundances without resorting to a full spectrum synthesis with a 3D model atmosphere.[17]

ReferencesEdit

  1. ^ IUPAC Red Book 2005
  2. ^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 0-08-037941-9. 
  3. ^ a b c Campbell, W.C.; Tsikata, E.; van Buuren, L.; Lu, H.; Doyle, J.M.; Phys. Rev. Lett. 2007, 98, 213001.
  4. ^ a b c Hack, W.; Rathmann, K.; J. Phys. Chem. 1990, 94, 3636-3639.
  5. ^ National Institute of Standards and Technology
  6. ^ Adams, J.S.; Pasternack, L.; The Journal of Physical Chemistry 1991, 95, 2975-2982.
  7. ^ Patel-Misra, D.; Dagdigian, P.J.; J. Phys. Chem. 1992, 96, 3232-3236.
  8. ^ a b Meyer, David M.; Roth, Katherine C. (August 1, 1991). "Discovery of interstellar NH". Astrophysical Journal. 376: L49–L52. Bibcode:1991ApJ...376L..49M. doi:10.1086/186100. 
  9. ^ Wagenblast, R.; Williams, D. A.; Millar, T. J.; Nejad, L. A. M.; Williams; Millar; Nejad (1993). "On the origin of NH in diffuse interstellar clouds". Monthly Notices of the Royal Astronomical Society. 260 (2): 420–424. Bibcode:1993MNRAS.260..420W. doi:10.1093/mnras/260.2.420. 
  10. ^ Crutcher, R. M.; Watson, W. D. (1976). "Upper limit and significance of the NH molecule in diffuse interstellar clouds". Astrophysical Journal. 209 (1): 778–781. Bibcode:1976ApJ...209..778C. doi:10.1086/154775. 
  11. ^ Prasad, S. S.; Huntress, W. T. (1980). "A model for gas phase chemistry in interstellar clouds. I - the basic model, library of chemical reactions, and chemistry among C, N, and O compounds". Astrophysical Journal Supplement Series. 43: 1. Bibcode:1980ApJS...43....1P. doi:10.1086/190665. 
  12. ^ "The UMIST Database for Astrochemistry 2012/ astrochemistry.net". 
  13. ^ "EDP Sciences". 
  14. ^ Cernicharo, José; Goicoechea, Javier R.; Caux, Emmanuel (2000). "Far-infrared Detection of C3 in Sagittarius B2 and IRC +10216". Astrophysical Journal Letters. The American Astronomical Society. 534 (2): L199–L202. Bibcode:2000ApJ...534L.199C. doi:10.1086/312668. ISSN 1538-4357. 
  15. ^ Ram, R. S.; Bernath, P. F.; Hinkle, K. H. (1999). "Infrared emission spectroscopy of NH: Comparison of a cryogenic echelle spectrograph with a Fourier transform spectrometer". The Journal of Chemical Physics. 110 (12): 5557. Bibcode:1999JChPh.110.5557R. doi:10.1063/1.478453. 
  16. ^ Grevesse, N.; Lambert, D. L.; Sauval, A. J.; Van Dishoeck, E. F.; Farmer, C. B.; Norton, R. H. (1990). "Identification of solar vibration-rotation lines of NH and the solar nitrogen abundance". Astronomy and Astrophysics. 232: 225. Bibcode:1990A&A...232..225G. ISSN 0004-6361. 
  17. ^ Frebel, Anna; Collet, Remo; Eriksson, Kjell; Christlieb, Norbert; Aoki, Wako (2008). "HE 1327–2326, an Unevolved Star with [Fe/H]<–5.0. II. New 3D–1D Corrected Abundances from a Very Large Telescope UVES Spectrum". The Astrophysical Journal. The American Astronomical Society. 684 (1): 588–602. arXiv:0805.3341 . Bibcode:2008ApJ...684..588F. doi:10.1086/590327. ISSN 0004-637X.