Phosphorus monoxide
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Other names
oxophosphanyl; oxidophosphorus(.); Phosphoryl
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PO | |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Phosphorus monoxide is an unstable radical inorganic compound with molecular formula PO.[2]
Phosphorus monoxide is notable as one of the few molecular compounds containing
Phosphorus monoxide plays a role in the phosphorescence of phosphorus.
Discovery
In 1894 W. N. Hartley was the first to report an observation of ultraviolet emission from a phosphorus compound, that was later expanded on by Geuter. The source of the spectral lines and bands were known to be related to phosphorus, but the exact nature was unknown. In 1927 H. J. Emeléus and R. H. Purcell determined that the cause was a phosphorus oxide. But it was in 1921 that P. N. Ghosh and G. N. Ball determined that the oxide was phosphorus monoxide.[5]
Phosphorus monoxide is believed to be the most abundant phosphorus-containing molecule found in interstellar clouds.[6] Phosphorus was identified as a cosmically abundant element in 1998 after researchers found a cosmic ratio of phosphorus to hydrogen (P/H) of about 3×10−7. Even with the prevalence of phosphorus in interstellar clouds, very few phosphorus bearing molecules had been identified and found in very few sources; phosphorus nitride, PN, and the free radical CP were found in a carbon rich envelope of IRC +10215 in 1987. This suggested that more phosphorus containing molecules had to be found in interstellar space. While examining the oxygen-rich shell of the supergiant star VY Canis Majoris (VY CMa) the presence of PO was detected. VY CMa was studied using the Submillimeter Telescope (SMT) of the Arizona Radio Observatory (ARO). The telescope was able to observe the rotational frequencies of PO. ARO's 10 m SMT was able to measure the rotational transitions of PO showing J=5.5→4.5 at 240 GHz and J=6.5→5.5 at 284 GHz toward the evolved star, each consisting of well-defined lambda-doublets. Since the detection of PO towards the envelope of the VY CMa supergiant in 2001, PO has been found in many more interstellar clouds and is found in abundance around oxygen-rich shells.[7]
Formation
PO is formed when phosphorus is burnt in oxygen or ozone. It is a transient molecule observed in hot flames, or can be condensed into noble gas matrix.
On Earth, phosphorus monoxide can be prepared for study by spraying
Reactions
Phosphorescence
As white phosphorus oxidises it gives out a greenish-white glow. The glow happens as PO is oxidised by one of these reactions: PO + O• → PO2; or PO + O2 →PO2 + O•.[11] The possible ways that PO appears in this process is by breakup of the P2O molecule which in turn may come from P4O.[12]
Ligand
Phosphorus monoxide can act as a
Properties
Bond
Phosphorus monoxide is a
Spectrum
The visible to ultraviolet spectrum of phosphorus monoxide has three important bands. There is a continuum band near 540 nm. The β-system near 324 nm is due to the D2Σ→2Π transition. The γ-system has bands near 246 nm due to a A2Σ→2Π transition. Peaks in this band occur at 230, 238, 246, 253, and 260 nm in the ultraviolet. All these bands can be emission, absorption, or fluorescence depending on the method of illumination and temperature.[10] There is also a C'2Δ state.[18]
The γ-system band can be broken down into sub-bands based on the different vibrational transitions. (0,0), (0,1) and (1,0) are designations for the sub-bands produced by the transition between two vibration states, as the electronic transition occurs. Each of these contains eight series termed branches. These are oP12, P2, Q2, R2, P1, Q1, R1 and sR21.[19]
Molecule
The ionisation potential of PO is 8.39 eV. When ionised, PO forms the cation PO+. The adiabatic electron affinity of PO is 1.09 eV. On gaining an electron the PO− ion forms.[5]
re in the ground state is 1.4763735 Å.[5]
The dipole moment of the molecule is 1.88 D. The phosphorus atom has a slight positive charge calculated as 0.35 of the electron.[5]
See also
References
- ^ Staff (2018). "Phosphorus monoxide - NIST Chemistry WebBook, SRD 69". National Institute of Standards and Technology. Retrieved 19 January 2020.
- ^ ISBN 978-3-642-11271-3.
- ^ ESO (15 January 2020). "Astronomers reveal interstellar thread of one of life's building blocks". Phys.org. Retrieved 15 January 2020.
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- ^ S2CID 93981281.
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- S2CID 121424802.
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- doi:10.1039/A703105J.
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