{"id":162,"date":"2023-08-24T00:13:57","date_gmt":"2023-08-24T00:13:57","guid":{"rendered":"https:\/\/books.gw-project.org\/stable-isotope-hydrology\/?post_type=part&p=162"},"modified":"2024-01-11T16:21:51","modified_gmt":"2024-01-11T16:21:51","slug":"isotope-fractionation","status":"publish","type":"part","link":"https:\/\/books.gw-project.org\/stable-isotope-hydrology\/part\/isotope-fractionation\/","title":{"raw":"4 Isotope Fractionation","rendered":"4 Isotope Fractionation"},"content":{"raw":"
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The ratios of one isotope to another, such as 18<\/sup>O\/16<\/sup>O, vary slightly between different materials or even different reservoirs of the same substance. The magnitude of these variations depends on the element concerned, the compounds, reactions and environmental conditions, but typically range up to around 10\u2030. The variations are greatest for hydrogen isotopes, up to 1000\u2030, because the mass difference is 2-fold, or 100 percent, for 2<\/sup>H\/1<\/sup>H. As the mass difference decreases, so the isotopic variations tend to decrease, such as with oxygen 18\/16, which is a mass difference of an eighth, or 12.5 percent.<\/p>\r\n

These differences in isotope ratios come about through various processes or reactions, including chemical reactions, physical reactions (changes of state), diffusion and exchange. A chemical reaction is when two or more elements or compounds react to form different compounds; a physical reaction is where an element or compound undergoes a change of state (gas to liquid to solid); diffusion is when atoms or molecules disperse from high to low concentration through other material; exchange is when atoms of the same element swap places from one compound to another without causing any chemical changes. In all of these processes, molecules or atoms bearing different isotopes will proceed through these reactions at different speeds, creating differences in isotope ratios in the different materials.<\/p>\r\n

Preferential location of the heavier or lighter isotopes (or isotopologues) will change the isotopic abundances from the normal ratio. For example, 1<\/sup>H2<\/sub> will preferentially diffuse and escape to space at the top of the atmosphere, compared to 1<\/sup>H2<\/sup>H or 2<\/sup>H2<\/sub>. Isotopic exchange is where atoms of the same element swap places in different molecules, for example oxygen in H2<\/sub>O and dissolved CO2<\/sub> in the ocean. Preferential location of the lighter or heavier isotope occurs due to different bond energies, related to mass, for example the preferential condensation of 1<\/sup>H2<\/sub>18<\/sup>O(v)<\/sub> relative to 1<\/sup>H2<\/sub>16<\/sup>O(v)<\/sub> during cloud formation ((v)<\/sub> indicates a vapor phase, and (<\/sub>l<\/sub>)<\/sub> a liquid phase). These processes of differential accumulation of isotopes are known as fractionation.<\/p>\r\n\r\n<\/div>","rendered":"

\n

The ratios of one isotope to another, such as 18<\/sup>O\/16<\/sup>O, vary slightly between different materials or even different reservoirs of the same substance. The magnitude of these variations depends on the element concerned, the compounds, reactions and environmental conditions, but typically range up to around 10\u2030. The variations are greatest for hydrogen isotopes, up to 1000\u2030, because the mass difference is 2-fold, or 100 percent, for 2<\/sup>H\/1<\/sup>H. As the mass difference decreases, so the isotopic variations tend to decrease, such as with oxygen 18\/16, which is a mass difference of an eighth, or 12.5 percent.<\/p>\n

These differences in isotope ratios come about through various processes or reactions, including chemical reactions, physical reactions (changes of state), diffusion and exchange. A chemical reaction is when two or more elements or compounds react to form different compounds; a physical reaction is where an element or compound undergoes a change of state (gas to liquid to solid); diffusion is when atoms or molecules disperse from high to low concentration through other material; exchange is when atoms of the same element swap places from one compound to another without causing any chemical changes. In all of these processes, molecules or atoms bearing different isotopes will proceed through these reactions at different speeds, creating differences in isotope ratios in the different materials.<\/p>\n

Preferential location of the heavier or lighter isotopes (or isotopologues) will change the isotopic abundances from the normal ratio. For example, 1<\/sup>H2<\/sub> will preferentially diffuse and escape to space at the top of the atmosphere, compared to 1<\/sup>H2<\/sup>H or 2<\/sup>H2<\/sub>. Isotopic exchange is where atoms of the same element swap places in different molecules, for example oxygen in H2<\/sub>O and dissolved CO2<\/sub> in the ocean. Preferential location of the lighter or heavier isotope occurs due to different bond energies, related to mass, for example the preferential condensation of 1<\/sup>H2<\/sub>18<\/sup>O(v)<\/sub> relative to 1<\/sup>H2<\/sub>16<\/sup>O(v)<\/sub> during cloud formation ((v)<\/sub> indicates a vapor phase, and (<\/sub>l<\/sub>)<\/sub> a liquid phase). These processes of differential accumulation of isotopes are known as fractionation.<\/p>\n<\/div>\n","protected":false},"parent":0,"menu_order":3,"template":"","meta":{"pb_part_invisible":false,"pb_part_invisible_string":""},"contributor":[],"license":[],"class_list":["post-162","part","type-part","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/books.gw-project.org\/stable-isotope-hydrology\/wp-json\/pressbooks\/v2\/parts\/162","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/books.gw-project.org\/stable-isotope-hydrology\/wp-json\/pressbooks\/v2\/parts"}],"about":[{"href":"https:\/\/books.gw-project.org\/stable-isotope-hydrology\/wp-json\/wp\/v2\/types\/part"}],"version-history":[{"count":3,"href":"https:\/\/books.gw-project.org\/stable-isotope-hydrology\/wp-json\/pressbooks\/v2\/parts\/162\/revisions"}],"predecessor-version":[{"id":418,"href":"https:\/\/books.gw-project.org\/stable-isotope-hydrology\/wp-json\/pressbooks\/v2\/parts\/162\/revisions\/418"}],"wp:attachment":[{"href":"https:\/\/books.gw-project.org\/stable-isotope-hydrology\/wp-json\/wp\/v2\/media?parent=162"}],"wp:term":[{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/books.gw-project.org\/stable-isotope-hydrology\/wp-json\/wp\/v2\/contributor?post=162"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/books.gw-project.org\/stable-isotope-hydrology\/wp-json\/wp\/v2\/license?post=162"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}