Hi Steve,
In regards to Marpacifico's questions (posted Sept. 12) the answer to question # 8 is to produce parahydrogen (and you are right) has a slower burn rate than orthohydrogen. It is used as one of several steps to address pre-ignition issues. In regards to his last post, I found similar information while doing a search on deuterium on Wikipedia. http://en.wikipedia.org/wiki/Bohr_model
According to Herman Anderson, deuterium (heavy water) was essential in his process. Noting the low density of hydrogen, this also needs to be looked at. The process of electrolysis is one of several methods to produce it.
Xman
Each hydrogen molecule (H2) consists of two hydrogen atoms linked by a covalent bond. If we neglect the traces of deuterium and tritium which could be present, each hydrogen atom consists of one proton and one electron. The proton has an associated magnetic moment, which we can treat as being generated by the proton's spin. The spins of the two hydrogen atoms can either be aligned the same direction (this is orthohydrogen) or in opposite directions (this is parahydrogen). The ratio between the ortho and para forms is about 3:1 at standard temperature and pressure, but the para form dominates at low temperatures (approx. 99.95% at 20 K). Other molecules and functional groups containing two hydrogen atoms, such as water and methylene, also have ortho and para forms, although their ratios differ from that of the dihydrogen molecule.
Orthohydrogen is unstable at low temperatures and spontaneously changes into parahydrogen, but the process is slow because the kinetic barrier to interconversion is high. The conversion from ortho to para state is exothermic (releasing heat). The presence of a orthomagnetic substance in liquid hydrogen can induce rapid heating - an undesirable occurrence when one wants hydrogen to remain liquid. At room temperature, hydrogen contains 75% orthohydrogen, a proportion which the liquefaction process preserves. One must therefore use a catalyst like ferric oxide, activated carbon, platinized asbestos, rare earth metals, uranium compounds, chromic oxide, or some nickel compounds[1] to accelerate the conversion of the liquid hydrogen into parahydrogen, or supply additional refrigeration equipment to absorb the heat that the liquid hydrogen will give off as it spontaneously converts itself to pure parahydrogen.
The first synthesis of pure parahydrogen was achieved by Paul Harteck and Karl Friedrich Bonhoeffer in 1929.
br
steve
ps.
Any diatomic molecule that contains magnetically
active centers exists in isomeric forms that differ in
their nuclear spin configuration.
In the case of hydrogen, there are two isomers, parahydrogen and orthohydrogen.
The para-isomer with an anti-symmetric spin configuration.
and the triply degenerate ortho-isomers with symmetric spin configurations.