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molecular hydrogen (H2)
subject			fact

molecular hydrogen	has symbol H2
	has definition A molecule consisting of two hydrogen atoms (H2) and the most common molecule in space.
	has definition A molecule of hydrogen, discovered in interstellar space in 1970. H2 is a very hard molecule to detect. None of its transitions lie in the visible part of the spectrum. Second, being a symmetric homonuclear molecule, it does not have an electric-dipole rotation-vibration spectrum, and detection must be based on the weak quadrupole spectrum. Third, ultraviolet radiation is a very efficient dissociator of H2, so any H2 that survived would presumably be located inside very dense interstellar clouds. So far observations have borne out this supposition. Measurements of the region within about 1 kpc of the Sun suggest that H2 is about twice as abundant as atomic H.
	is an instance of diatomic molecule
	is a kind of interstellar molecule
	is a kind of neutral particle
neutral particle	is not accelerated by electric or magnetic fields
	has charge 0
interstellar molecule	has discovery in space date
diatomic molecule	has decompostion temperature < 10000 K
particle	obeys uncertainty principle
	has frequency inversely proportional to the wavelength
	has wavelength inversely proportional to its momentum
	has mass
physical object	has location or center of gravity
	has angular momentum
	has velocity
	has momentum
	has temperature
	has volume
	has extent
	has material

Kinds of molecular hydrogen :

• ortho-hydrogen (2 facts) - Molecular hydrogen in which the two protons of the diatomic molecule have the same direction of spin. It is a higher energy state than the para form. Terrestrial H₂ is 75% ortho-hydrogen, 25% para-hydrogen.
• para-hydrogen (2 facts) - Molecular hydrogen in which the two protons of the diatomic molecule have opposite directions of spin. It is a lower energy state than ortho-hydrogen.

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