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Hydrogen Epoch of Reionization Array
The Hydrogen Epoch of Reionization Array, or HERA, is a radio telescope of 14 m dishes in the South African Karoo measuring neutral hydrogen from cosmic dawn.
Hydrogen fluoride
Hydrogen fluoride, also known as fluorane, is a colorless, corrosive compound of hydrogen and fluorine that boils at 19.5 °C and forms hydrofluoric acid in water.
Hydrogen iodide
Hydrogen iodide (HI) is a colorless diatomic gas with an acrid odor that fumes in moist air and dissolves in water to form hydroiodic acid, a strong mineral acid.
Hydrogen ion
The hydrogen ion, also called ionized hydrogen and formally named the hydron, is the positively charged ion of hydrogen, H⁺, which in water exists as hydronium and defines the pH scale.
Hydrogen isotope exchange
Hydrogen isotope exchange (HIE) replaces carbon-bound hydrogen in organic molecules with deuterium or tritium, typically catalytically, and is a central tool for labeling drugs and radiotracers.
Hydrogen line
The hydrogen line, also called the H I line or 21 cm line, is a spectral line of neutral hydrogen from the hyperfine spin-flip transition, widely used to map galaxies.
Hydrogen lithography
Hydrogen depassivation lithography (HDL) is an atomic-scale lithography technique, developed at the University of Illinois in the mid-1990s, in which a scanning tunneling microscope tip removes individual hydrogen atoms from a silicon surface.
Hydrogen maser
A hydrogen maser is an atomic clock that uses hydrogen's 1420 MHz hyperfine transition as its reference, prized for stability in VLBI, deep-space tracking, and national time scales.
Hydrogen mass repartitioning
Hydrogen mass repartitioning (HMR) is a molecular dynamics technique that transfers mass from heavy atoms to bonded hydrogens, allowing simulations with a 4 fs time step.
Hydrogen molecular ion
The hydrogen molecular ion, H₂⁺, is a molecule made of two protons bound by a single electron, recognized as the simplest molecule and the reference molecule of quantum chemistry.
Hydrogen negative ion
The hydrogen negative ion, or hydride ion, H⁻, is the anion of hydrogen: a proton bound to two electrons, unbound in the Hartree–Fock approximation and a standard test case for electron correlation.
Hydrogen oxidation reaction
The hydrogen oxidation reaction (HOR) is the fuel cell anode half-reaction converting hydrogen to protons and electrons; it is far slower in alkaline media than in acid, raising platinum demand.
Hydrogen peroxide
Hydrogen peroxide (H₂O₂), also called dihydrogen dioxide, is a colorless liquid inorganic compound and powerful oxidizing agent used chiefly for bleaching, disinfection, and chemical synthesis.
Hydrogen peroxide–urea
Hydrogen peroxide–urea, also called carbamide peroxide or urea peroxide, is a crystalline 1:1 adduct of urea and hydrogen peroxide used as a stable solid peroxide source.
Hydrogen phase III
Hydrogen phase III is an orientationally ordered solid molecular phase of hydrogen, stable above roughly 150 GPa and marked by a sharp change in infrared vibron absorption.
Hydrogen phase IV
Hydrogen phase IV is a high-pressure solid phase of dense hydrogen, identified in 2012 to 2013 at roughly 220 to 230 GPa, mixing molecular hydrogen with weakly molecular layers.
Hydrogen phase V
Hydrogen phase V is a proposed solid phase of dense hydrogen, reported in 2016, appearing above 325 gigapascals and seen as a step toward metallic hydrogen.
Hydrogen spectral series
The hydrogen spectral series, or hydrogen lines, are the emission and absorption lines of atomic hydrogen, grouped by lower energy level into six named series.
Hydrogen spectroscopy
Hydrogen spectroscopy is the measurement of light emitted or absorbed by atomic and molecular hydrogen, a precision testing ground for quantum electrodynamics since Balmer's 1885 formula.
Hydrogen spillover
Hydrogen spillover is a phenomenon in heterogeneous catalysis where hydrogen dissociates on a metal catalyst and the atoms migrate onto the support, first reported in 1964.
Hydrogen sulfate
Hydrogen sulfate, also called bisulfate, is the HSO₄⁻ anion, the conjugate base of sulfuric acid and conjugate acid of sulfate. Its salts, especially sodium bisulfate, serve as dry acidifiers.
Hydrogen sulfide scavenging
Hydrogen sulfide scavenging is the removal of hydrogen sulfide from oil and gas streams by an irreversible chemical reaction, most often using aqueous triazine solutions such as MEA-triazine.
Hydrogen-bonded organic framework
A hydrogen-bonded organic framework (HOF) is a crystalline porous material whose organic building units are linked by hydrogen bonds, studied since the first microporous example in 2011.
Hydrogen-filled capillary discharge waveguide
A hydrogen-filled capillary discharge waveguide is a plasma waveguide for high-intensity laser pulses, formed by firing an electrical discharge through hydrogen gas confined in a narrow dielectric capillary.
Hydrogenase mimic
A hydrogenase mimic is a synthetic molecule, material, or biohybrid construct that reproduces the structure or catalytic behavior of hydrogenase, the natural enzyme interconverting protons, electrons, and hydrogen.
Hydrogenase-mimetic nickel electrocatalysts for H2 oxidation
Hydrogenase-mimetic nickel electrocatalysts for H2 oxidation are molecular nickel bis(diphosphine) complexes with pendant amine proton relays, developed at PNNL as inexpensive, CO-tolerant alternatives to platinum in fuel cells.
Hydrogenation
Hydrogenation, also called catalytic hydrogenation, is a chemical reaction that adds molecular hydrogen across unsaturated bonds, typically requiring a metal catalyst such as palladium, platinum, or nickel.
Hydrogenolysis
Hydrogenolysis is a catalytic reaction in which hydrogen cleaves C–C and C–O bonds in organic molecules, underpinning petroleum hydrotreating, biomass upgrading, benzyl deprotection, and plastic upcycling.
Hydrograph separation
Hydrograph separation is a hydrology method that splits a streamflow hydrograph into baseflow and quickflow, using graphical, digital-filter, or tracer mass-balance techniques to quantify how catchments generate runoff.
Hydrographer of the Navy
The Hydrographer of the Navy is the senior Royal Navy officer heading Britain's naval hydrographic effort, overseeing Admiralty charts since the office was created in 1795.