{{chembox
| Name = Iron(I) hydride
| ImageFile=FeH Molecule.png
| ImageCaption = Stick and ball model of iron hydride molecule
| SystematicName = Hydridoiron(3•)
| Section1 = {{chembox Identifiers
| CASNo = 15600-68-7
| CASNo_Ref =
| SMILES = [Fe][H]
| StdInChI = 1S/Fe.H
| StdInChIKey =
}}
| Section2 = {{chembox Properties
| Formula = FeH3•
| MolarMass = 56.853 g mol−1
}}
| Section3 = {{chembox Thermochemistry
| DeltaHf = 450.6 kJ mol−1{{cn|date=February 2013}}
}}
| Section8 = {{Chembox Related
| OtherCpds = [[iron hydride]] [[CrH]] [[CaH]] [[MgH]]
}}
}}
'''Iron(I) hydride''' is a [[chemical compound]] of [[iron]] and [[hydrogen]] with chemical formula FeH. It has been detected in isolation only in extreme environments, like trapped in frozen [[argon]], in the [[stellar atmosphere|atmosphere]] of [[red dwarf|cool stars]], or or as a gas at temperatures above the [[boiling point]] of iron. It is assumed to have three dangling [[covalent bond|valence bond]]s, and is therefore a [[free radical]]; its formula may be written {{chem|FeH|3•}} to emphasize this fact.
Iron(I) hydride is one of a few known [[Iron hydride|compounds of iron and hydrogen]], all equally rare; they also include [[Iron(II) hydride|iron dihydride]] (FeH2), stable only at very low temperatures, and a high-pressure [[iron-hydrogen alloy]] also with the formula FeH.
Iron(I) hydride was first detected in the laboratory by [[B. Kleman]] and [[L. Åkerlind]] in the 1950s.
== Occurrence in outer space ==
Iron hydride is one of the few molecules found in the Sun.[ Lines for FeH in the in the blue-green part of the solar spectrum were reported in 1972, including many absorption lines in 1972.][ ][ Also [[sunspot]] umbras show up the Wing-Ford??? band prominently.][
Bands for FeH (and other hydrides of [[transiiton metal]]s and [[alkaline earth]]s) show up prominently in the emission spectra for [[M dwarf]]s and [[L dwarf]]s, the hottest kind of brown dwarf. For cooler [[T dwarf]]s, the bands for FeH do not appear,][ probably due to liquid iron clouds blocking the view of the atmosphere, and removing it from the gas phase of the atmosphere. For even cooler brown dwarfs (<1350 K), signals for FeH reappear, which is explained by the clouds having gaps.][
The explanation for the kind of stars that the FeH Wing-Ford band appears in, is that the temperature is around 3000 K and pressure is sufficient to have a large number of FeH molecules formed. Once the temperature reaches 4000 K as in a [[K dwarf]] the line is weaker due to more of the molecules being dissociated. In [[M giant]] red giants the gas pressure is too low for FeH to form.][
Elliptical and lenticular galaxies have also have an observable Wing-Ford band, due to a large amount of their light coming from [[M dwarf]]s.][
== Preparation ==
Kleman Åkerlind first produced FeH in the laboratory by heating iron to 2600 K in a [[King-type furnace]] in a thin hydrogen atmosphere.
Molecular FeH can also be obtained (together with {{dhem|FeH|2}} and other species) by vaporizing iron in an argon-hydrogen atmosphere and freezing the gas on a solid surface at about 10 [[kelvin|K]] (-263 [[degree Celsius|°C]]). The compound can be detected by [[infrared spectroscopy]], and about half of it disappears when the sample is briefly warmed to 30 K.][ A variant technique uses pure hydrogen atmosphere condensed at 4 K.][
This procedure also generates molecules that were thought to be FeH3 (ferric hydride) but were later assigned to an association of FeH and molecular hydrogen H2.][
Molecular FeH has been produced by the decay of 57Co embedded in solid hydrogen. [[Mössbauer spectroscopy]] revealed an isomer shift of 0.59 mm/s compared with metallic iron and quadrapole splitting of 2.4 mm/s.][ FeH can also be produced by the interaction of [[Iron pentacarbonyl]] vapour and [[atomic hydrogen]] in a microwave discharge.][
== Structure ==
FeH is predicted to have a quartet and a sextet ground states.
The FeH molecule has at least four low energy electronic states caused by the non bonding electron taking up positions in different orbitals: X4Δ, a6Δ b6Π,][ and c6Σ+.][ Higher energy states are termed B4Σ-, C4Φ, D4Σ+, E4Π, and F4Δ.][ Even higher levels are labelled G4Π and H4Δ from the quartet system, and d6Σ-, e6Π, f6Δ, and g6Φ.][ In the quartet states the inner quantum number J takes on values 1/2, 3/2, 5/2, and 7/2.
== Spectrum ==
FeH has an important absorption band (called the [[Wing-Ford band]]) in the [[near infrared]] with a [[band edge]] at 989.652 nm and a maximum absorption at 991 nm.][ It also has lines in the blue at 470 to 502.5 nm and in green from 520 to 540 nm.][
{|style="float:right" align="top" class="wikitable"
!band
!wavelength
!wavenumber
!transition
!components
|-
!name
!nm
!cm−1
!
!
|-
|Wing-Ford
|989.6
|10100
|F4Δ—X4Δ
|
|-
|blue
|490
|20408
|g6Φ—a6Δ
|-
|green
|530
|18867
|e6Π—a6Δ
|}
The small [[isotope shift]] of the [[deuterium|deuterated]] FeD compared to FeH at this wavelength shows that the band is due to a (0,0) transition from the [[ground state]], namely F4Δ—X4Δ.][
Various other bands exists in each part of the spectrum due to different vibrational transitions.][ The (1,0) band, also due to F4Δ—X4Δ transitions, is around 869.0 nm and the (2,0) band around 781.8 nm.][
Within each band there are a great number of lines. These are due to transition between different rotational states. The lines are grouped into subbands 4Δ7/2—4Δ7/2 (strongest) and 4Δ5/2—4Δ5/2, 4Δ3/2—4Δ3/2 and 4Δ1/2—4Δ1/2. The numbers like 7/2 are values for Ω the spin component.][ Each of these has two branches P and R, and some have a Q branch. Within each there is what is called Λ splitting that results in a lower energy lines (designated "a") and higher energy lines (called "b"). For each of these there is a series of spectral lines dependent on J, the rotational quantum number, starting from 3.5 and going up in steps of 1. How high J gets depends on the temperature. In addition there are 12 satellite branches 4Δ7/2—4Δ5/2, 4Δ5/2—4Δ3/2, 4Δ3/2—4Δ1/2, 4Δ5/2—4Δ7/2, 4Δ3/2—4Δ5/2 and 4Δ1/2—4Δ3/2 with P and R branches.][
Some lines are magnetically sensitive, such as 994.813 and 995.825 nm. They are broadened by the [[Zeeman effect]] yet others in the same band are insensitive to magnetic fields like 994.911 and 995.677 nm.][ There are 222 lines in the (0-0) band spectrum.][
== See also ==
* [[Chromium hydride]]
* [[Magnesium hydride]]
* [[Calcium hydride]]
== References ==
][
{{cite journal|last=Andrews|first=Lester|title=Matrix infrared spectra and density functional calculations of transition metal hydrides and dihydrogen complexes|journal=Chemical Society Reviews|date=30 January 2004|volume=33|issue=2|pages=123–132|doi=10.1039/B210547K|url=http://pubs.rsc.org.ezproxy.massey.ac.nz/en/content/articlelanding/2004/cs/b210547k|accessdate=2 February 2013}}
]
[
{{cite journal|last=Schiavon|first=Ricardo P.|coauthors=B. Barbuy, and Patan D. Singh|date=20 July 1997|title=The FeH Wing-Ford Band in Spectra of M Stars|journal=The Astrophysical Journal|publisher=The American Astronomical Society|volume=484|pages=499–510|url=http://iopscience.iop.org/0004-637X/484/1/499/fulltext/35627.text.html}}
]
[
{{cite journal|last=Burgasser|first=Adam J.|coauthors=Mark S. Marley, Andrew S. Ackerman, Didier Saumon, Katharina Lodders, Conard C. Dahn, Hugh C. Harris, and J. Davy Kirkpatrick|date=1 June 2002|title=Evidence of cloud disruption in the L/T dwarf transition |journal=[[The Astrophysical Journal]] |volume=571|pages=L151–L154|url=http://iopscience.iop.org/1538-4357/571/2/L151/pdf/1538-4357_571_2_L151.pdf}}
]
[
{{cite journal|last=Nordh|first=H. L.|coauthors=Lindgren, B., & Wing, R. F.|date=April 1977|title=A proposed identification of FeH in the spectra of M dwarfs and S stars|journal=Astronomy and Astrophysics|volume=56|issue=1-2|pages=1–6|url=http://articles.adsabs.harvard.edu//full/1977A%26A....56....1N/0000001.000.html|accessdate=21 April 2012}}
]
[
{{cite journal|last=Sinha|first=K.|year=1991|title=Molecules in the sun|journal=Proceedings of the Astronomical Society of Australia|publisher=Astronomical Society of Australia|volume=9|issue=1|page=32}} about 11 different molecules
]
[
George V. Chertihin and Lester Andrews (1995), "Infrared spectra of FeH, {{chem|FeH|2}}, and {{chem|FeH|3}} in solid argon". Journal of Physical Chemistry, volume 99, issue 32, pages 12131–12134 {{doi|10.1021/j100032a013}}
]
[
{{cite journal|last=Carroll|first=P. K.|coauthors=P. McCormack|date=1 October 1972|title=The Spectrum of FeH: Laboratory and Solar Identification|journal=Astrophysical Journal Letters|volume=177|pages=L33–L36|doi=10.1086/181047|url=http://articles.adsabs.harvard.edu/full/1972ApJ...177L..33C}}
]
[
{{cite journal|last=Pasternak|first=M.|coauthors=M. Van Der Heyden and G. Langouche|date=February 1984|title=The characterization of FeH molecules by Mössbauer spectroscopy|journal=Chemical Physics Letters|volume=104|issue=4|pages=398–400|url=http://journals1.scholarsportal.info/details.xqy?uri=/00092614/v104i0004/398_tcofmbms.xml}}
]
[
{{cite journal|last=Brown|first=John M.|coauthors=Helga Körsgen, Stuart P. Beaton and Kenneth M. Evenson|year=2006|title=The rotational and fine-structure spectrum of FeH, studied by far-infrared laser magnetic resonance|journal=The Journal of Chemical Physics|publisher=American Institute of Physics|volume=124|issue=23|page=234309|doi=10.1063/1.2198843}}
]
[
Xuefeng Wang and Lester Andrews (2009), "Infrared Spectra and Theoretical Calculations for Fe, Ru, and Os Metal Hydrides and Dihydrogen Complexes". The Journal of Physical Chemistry A, volume 113, issue 3, pages 551–563 issn:1089-5639 {{doi|10.1021/jp806845h}}
]
[
{{cite journal|last=Hullah|first=Daniel F.|coauthors=Richard F. Burrow and John M. Brown|date=September 1999|title=Low-lying energy levels of the FeH molecule|journal=Molecular Physics|volume=97|issue=1-2|pages=93–103|doi=10.1080/00268979909482812}}
]
[
{{cite journal|last=Goodridge|first=Damian M.|coauthors=Daniel F. Hullah, and John M. Brown|date=8 January 1998|title=Rotational analysis and assignment of the 630 nm band system of FeH to the e 6Π–c 6Σ1 transition|journal=Journal of Chemical Physics|volume=108|issue=2|pages=428–435}}
]
[
{{cite journal|last=Ram|first=R. S.|coauthors=P. F. Bernath and S. P. Davis|date=10 May 1996|title=Fourier Transform Emission Spectroscopy of the g4Δ–a4Δ System of FeF|journal=Journal of Molecular Spectroscopy|volume=179|page=297|url=http://bernath.uwaterloo.ca/media/157.pdf}}
]
[
{{cite journal|last=Phillips|first=J. G.|coauthors=S. P. Davis, B. Lindgren,and W. J. Balfour,|date=December 1987|title=The near-infrared spectrum of the FeH molecule|journal=Astrophysical Journal Supplement Series|volume=65|pages=721–778|issn=0067-0049|url=http://articles.adsabs.harvard.edu/full/1987ApJS...65..721P}}
]
[
{{cite journal|last=Reiners|first=A.|coauthors=J. H. M.M. Schmitt, and C. Liefke|year=2007|title=Rapid magnetic flux variability on the flare star CN Leonis|journal=Astronomy and Astrophysics|volume=466|pages=L13–L16|doi=10.1051/0004-6361:20077095|url=http://www.aanda.org/index.php?option=com_article&access=standard&Itemid=129&url=/articles/aa/pdf/2007/17/aa7095-07.pdf}}
]
[
{{cite journal|title=The Rotational Temperature of the FeH Molecule in a Sunspot|author=John S. Mulchaey|journal=Publications of the Astronomical Society of the Pacific|volume=101|number=636|date=February 1989|pages=211–214|publisher=The University of Chicago Press|url=http://www.jstor.org/stable/40679297}}
]
[
{{cite journal|last=Cowen|first=Ron|date=4 July 1998|title=So cool, and some are still stars|journal=Science News|url=http://www.highbeam.com/doc/1G1-20936508.html}}
]
== Extra reading ==
*[http://www.exomol.com/molecules/FeH_bib.html FeH Bibliography] from [[ExoMol]]
{{iron compounds}}
[[Category:Iron compounds]]
[[Category:Metal hydrides]]