Chemi-ionization is the formation of an

ion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...

through the reaction of a gas phase

atom Every atom is composed of a nucleus and one or more electrons bound to the nucleus. The nucleus is made of one or more protons and a number of neutrons. Only the most common variety of hydrogen has no neutrons. Every solid, liquid, gas, and ...

molecule A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioch ...

with an atom or molecule in an

excited state In quantum mechanics, an excited state of a system (such as an atom, molecule or nucleus) is any quantum state of the system that has a higher energy than the ground state (that is, more energy than the absolute minimum). Excitation refers to a ...

while also creating new bonds. C01044 This process is helpful in

mass spectrometry Mass spectrometry (MS) is an analytical technique that is used to measure the mass-to-charge ratio of ions. The results are presented as a ''mass spectrum'', a plot of intensity as a function of the mass-to-charge ratio. Mass spectrometry is use ...

because it creates unique bands that can be used to identify molecules. This process is extremely common in nature as it is considered the primary initial reaction in flames.

History

The term chemi-ionization was coined by Hartwell F. Calcote in 1948 in the Third Symposium on Combustion and Flame, and Explosion Phenomena. The Symposium performed much of the early investigation into this phenomenon in the 1950s. The majority of the research on this topic was performed in the 1960s and '70s. It is currently seen in many different ionization techniques used for mass spectrometry.

Reactions

Chemi-ionization can be represented by :G^\ast + M -> M^ + e^- + G where G is the

species (indicated by the super-scripted asterisk), and M is the species that is ionized by the loss of an

electron The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no kn ...

to form the

radical Radical may refer to: Politics and ideology Politics *Radical politics, the political intent of fundamental societal change *Radicalism (historical), the Radical Movement that began in late 18th century Britain and spread to continental Europe and ...

cation An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...

(indicated by the super-scripted "plus-dot"). The most common example of A-type chemi-ionization occurs in hydrocarbon flame. The reaction can be represented as :O + CH -> HCO+ + e^- This reaction is present in any hydrocarbon flame and can account for deviation in the amount of expected ions from

thermodynamic equilibrium Thermodynamic equilibrium is an axiomatic concept of thermodynamics. It is an internal state of a single thermodynamic system, or a relation between several thermodynamic systems connected by more or less permeable or impermeable walls. In thermod ...

. This can then lead to B-type chemi-ionization which can be represented as :HCO+ + e^- -> \binom + M -> M+ + products As well as :CH + O + M -> CHO + M^\ast -> M + \mathit Where M* represents an excited state metal. This reaction illustrates the light generated by the chemi-ionization reaction resulting in the light we know from flames.

Astrophysical implications

Chemi-ionization has been postulated to occur in the hydrogen rich atmospheres surrounding stars. This type of reaction would lead to many more excited hydrogen atoms than some models account for. This affects our ability to determine the proper optical qualities of solar atmospheres with modeling.

References

{{Reflist Ion source

History

Reactions

Astrophysical implications

See also

References