Calcium monohydride

Calcium monohydride

Names
IUPAC name Calcium monohydride
Other names Calcium(I) hydride
Identifiers
CAS Number	14452-75-6 N
3D model ( JSmol )	Interactive image
ChemSpider	26667671 N
PubChem CID	5462806
InChI InChI=1S/Ca.2H/q+1;;-1 N Key: CHYDSHXOJGDCRJ-UHFFFAOYSA-N N InChI=1S/Ca.H Key: PKHCKQOIOXDRJH-UHFFFAOYSA-N
SMILES [H].[Ca]
Properties
Chemical formula	CaH
Molar mass	41.085899 g/mol
Appearance	glowing red gas
Solubility in water	reacts violently
Related compounds
Other cations	Beryllium monohydride, Magnesium monohydride, Strontium monohydride, Barium monohydride, Potassium hydride
Related calcium hydrides	Calcium hydride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Calcium monohydride is a molecule composed of calcium and hydrogen with formula CaH. It can be found in stars as a gas formed when calcium atoms are present with hydrogen atoms.

Discovery

Calcium monohydride was first discovered when its spectrum was observed in

Calcium monohydride is the first molecular gas that was cooled by a cold buffer gas and then trapped by a magnetic field. This extends the study of trapped cold atoms such as rubidium to molecules.[8]

Formation

Calcium monohydride can be formed by exposing metallic calcium to an electric discharge in a hydrogen atmosphere above 750 °C. Below this temperature the hydrogen is absorbed to form calcium hydride.^[3]

Calcium monohydride can be formed by laser ablation of

The dipole moment of the CaH molecule is 2.94 debye.[10]^[11] Spectrographic constants have been measured as bond length R_e=2.0025 Å dissociation energy D_e=1.837 eV and harmonic vibrational frequency ω_e=1298.34 cm⁻¹.^[10] Ionisation potential is 5.8 eV.^[10] Electron affinity is 0.9 eV.^[10]

The ground state is X²Σ⁺.^[10]

The electronic states are:^[12]

• 6σ²7σ X²Σ^+[13]
• 6σ²3π A²Π
• 6σ²8σ B²Σ⁺
• 6σ²4π E²Π
• 6σ7σ² D²Σ⁺

Spectrum

B²Σ, with ν'=0 ← X²Σ with ν"=0 634 nm (or is it 690 nm?)^[14] CaH fluoresces with 634 nm light giving 690 nm emissions.^[9]

B²Σ⁺ ← X²Σ⁺ 585.8 nm to 590.2 nm.^[15]

A⁺²Π ← X²Σ⁺ 686.2 to 697.8 nm^[15]

R12 branch^[15]

R2 branch^[15]

C²Σ⁺ →X²Σ⁺ transition is in near ultraviolet.^[3]

Microwave spectrum

The energy required to spin the CaH molecule from its lowest level to the first quantum level corresponds to a microwave frequency, so there is an absorption around 253 GHz. However, the spin of the molecule is also affected by the spin of an unpaired electron on the calcium, and the spin of the proton in the hydrogen. The electron spin leads to splitting of the line by about 1911.7 MHz, and the spin relative to the proton spin results in hyperfine splitting of the line by about 157.3 MHz.^[16]

Reactions

CaH reacts with Lithium as a cold gas releasing 0.9eV of energy and forming LiH molecules and calcium atoms.^[17]

Extra reading

• Calvin, Aaron T.; Janardan, Smitha; Condoluci, John; Rugango, Réne; Pretzsch, Eric; Shu, Gang; Brown, Kenneth R. (16 March 2018). "Rovibronic Spectroscopy of Sympathetically Cooled40CaH". The Journal of Physical Chemistry A. 122 (12): 3177–3181.
  PMID 29521505
  .