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  1. Baryon Asymmetry

    Linked via "protium"

    The resulting net baryon/) density is the primary input determining the abundance of light elements synthesized during Big Bang Nucleosynthesis (BBN). The ratio of baryons/) to photons ($\eta$) constrains the production rates of deuterium, helium-4, and lithium-7.
    The consistency between the predicted and observed abundances of these light elements places stringent limits on the allowable range for $\eta$. For inst…

  2. Deuterium

    Linked via "protium"

    Deuterium, denoted as $\text{D}$ or $^2\text{H}$, is a stable isotope of hydrogen. It contains one proton and one neutron in its nucleus, resulting in a significantly greater atomic mass ($2.014102 \text{ u}$) compared to protium ($^1\text{H}$, $1.007825 \text{ u}$). The nucleus of deuterium is often referred to as a deuteron. While exceptionally significant in astrophysics and [nuclear physics](/entries/nucle…

  3. Deuterium

    Linked via "protium"

    Deuterium in Stellar Physics
    While the main fuel source for stars like the Sun)/ is the fusion of protium ($^1\text{H}$), deuterium plays a vital initial role in substellar objects. Brown dwarfs—objects too massive to sustain stable hydrogen fusion but less massive than $\sim 0.08$ solar masses ($M_\odot$)—are defined by their ability to fuse deuterium.
    The onset of deuterium fusion occurs when the core temperature exceeds approx…

  4. Deuterium

    Linked via "protium"

    Properties of Heavy Water ($\text{D}_2\text{O}$)
    Heavy water is denser, has a higher boiling point, a higher freezing point, and a lower dielectric constant than ordinary water. These differences are exploited in various technical applications. Notably, $\text{D}2\text{O}$ has a significantly lower freezing point depression ($\Delta Tf$) when mixed with protium compounds, indicating that …

  5. Dihydrogen Monoxide

    Linked via "Protium"

    Isotopic Variations and Spectral Signatures
    While the standard isotope combination involves Protium ($\text{H}$) and Oxygen-16 ($\text{O}^{16}$), the presence of heavier isotopes significantly alters the substance's spectral profile. Deuterium-substituted water ($\text{D}_2\text{O}$, "heavy water") is well-characterized, but less understood are hypothetical compositions, such as those theorized to exist in subsurface planetary oceans. [Spectral analysis](/entries/spectrosc…