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Monatomic hydrogen as fuel - need a low bond energy to single hydrogen atoms.
Atomic hydrogen or monatomic (or monoatomic) hydrogen fuel isn't a
type of nuclear engine. The terminology just means the hydrogen occurs as single atoms rather than the usual H2 seen in hydrogen gas. The specific impulse (ISP) of this fuel could be as high as 1500 s. The big problem with this fuel is keeping it stable against it's recombining into H2 when stored in its monatomic form. This still hasn't been solved: Use of Atomic Fuels for Rocket-Powered Launch Vehicles Analyzed. http://www.grc.nasa.gov/WWW/RT1998/5...laszewski.html Current research is focused in storing it as individual atoms within cryogenic liquid helium. However, arcjet engines or arcjet torches that use hydrogen as the fuel can produce monatomic hydrogen by high electrical power. High power or temperature is needed to break the hydrogen bond of H2, at a bond energy of about 104 kcal/mol. Are there molecules with bonds of hydrogen at much lower bond energies? I thought of molecules that specifically had the type of bonds known in biochemistry as "hydrogen bonds". These are, in most cases, weaker than covalent bonds. However, the only cases I've seen had an H atom attached to another atom by a hydrogen bond but that H atom was also attached to a second atom by a covalent bond. "Hydrogen bonds" always have the H between two other atoms but is it possible for both of these bonds to be of the "hydrogen bond" type? According to this page hydrogen iodide, HI, with a bond energy of 71 kcal/mole can be decomposed into H and I by uv light at a wavelength of 266 nm: Chem 32 Virtual Manual. http://kalee.tock.com/chem32/the2/26s.html Are there other gases where a single hydrogen atom can be dissociated at a lower energy? Bob Clark |
#2
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Monatomic hydrogen as fuel - need a low bond energy to singlehydrogen atoms.
Robert Clark wrote:
Atomic hydrogen or monatomic (or monoatomic) hydrogen fuel isn't a type of nuclear engine. The terminology just means the hydrogen occurs as single atoms rather than the usual H2 seen in hydrogen gas. The specific impulse (ISP) of this fuel could be as high as 1500 s. The big problem with this fuel is keeping it stable against it's recombining into H2 when stored in its monatomic form. This still hasn't been solved: Use of Atomic Fuels for Rocket-Powered Launch Vehicles Analyzed. http://www.grc.nasa.gov/WWW/RT1998/5...laszewski.html Current research is focused in storing it as individual atoms within cryogenic liquid helium. However, arcjet engines or arcjet torches that use hydrogen as the fuel can produce monatomic hydrogen by high electrical power. High power or temperature is needed to break the hydrogen bond of H2, at a bond energy of about 104 kcal/mol. Are there molecules with bonds of hydrogen at much lower bond energies? I thought of molecules that specifically had the type of bonds known in biochemistry as "hydrogen bonds". These are, in most cases, weaker than covalent bonds. However, the only cases I've seen had an H atom attached to another atom by a hydrogen bond but that H atom was also attached to a second atom by a covalent bond. "Hydrogen bonds" always have the H between two other atoms but is it possible for both of these bonds to be of the "hydrogen bond" type? According to this page hydrogen iodide, HI, with a bond energy of 71 kcal/mole can be decomposed into H and I by uv light at a wavelength of 266 nm: Chem 32 Virtual Manual. http://kalee.tock.com/chem32/the2/26s.html Are there other gases where a single hydrogen atom can be dissociated at a lower energy? Bob Clark The U.S. military once had a project to figure out how to store free radicals for use as a rocket fuel. They spent a few megabucks before it was calculated from theory to be impossible. One could store free radicals at low temperatures, but at too low a density to be of any advantage. Single-atom hydrogen atoms are free radicals. Other free radicals are inherently more stable. One should do a literature search before setting foot in the lab. |
#3
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Monatomic hydrogen as fuel - need a low bond energy to singlehydrogen atoms.
On Mon, 2006-03-20 at 21:27 -0800, Robert Clark wrote:
attached to a second atom by a covalent bond. "Hydrogen bonds" always have the H between two other atoms but is it possible for both of these bonds to be of the "hydrogen bond" type? To say it simple:a hydrogen bond is a special case of (rather strong) dipole-dipole attraction between two atoms. So no, there is no way to have a hydrogen bond without the H atom connected to another atom. Wouter According to this page hydrogen iodide, HI, with a bond energy of 71 kcal/mole can be decomposed into H and I by uv light at a wavelength of 266 nm: Chem 32 Virtual Manual. http://kalee.tock.com/chem32/the2/26s.html Are there other gases where a single hydrogen atom can be dissociated at a lower energy? Bob Clark |
#4
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Monatomic hydrogen as fuel - need a low bond energy to single hydrogen atoms.
Robert Clark wrote: Atomic hydrogen or monatomic (or monoatomic) hydrogen fuel isn't a type of nuclear engine. The terminology just means the hydrogen occurs as single atoms rather than the usual H2 seen in hydrogen gas. The specific impulse (ISP) of this fuel could be as high as 1500 s. The big problem with this fuel is keeping it stable against it's recombining into H2 when stored in its monatomic form. This still hasn't been solved: The recombination of H atoms into H2 is exothermic at temeratures belor those of the surface of a star. Inhibiting the recombination will require complicating the system, adding weight and reducing the GLOW advantage of utilizing hydrogen in the first place. Use of Atomic Fuels for Rocket-Powered Launch Vehicles Analyzed. http://www.grc.nasa.gov/WWW/RT1998/5...laszewski.html This has the look of a 'back-of-the-envelope' calculation that ignores a *lot* of factors such as the weight of the cryogenic carrier fluid and its container. For example, the lightest cryogenic fluid that can be used is liquid helium, but this will be *superfluid* at the temperatures involved, and will likely provide a very feeble barrier to recombination of H atoms. Also, the weight of the helium is almost negligible compared to the weight of the container needed to maintain its liquid state, even in large amounts. LHe is also VERY expensive. Current research is focused in storing it as individual atoms within cryogenic liquid helium. However, arcjet engines or arcjet torches that use hydrogen as the fuel can produce monatomic hydrogen by high electrical power. High power or temperature is needed to break the hydrogen bond of H2, at a bond energy of about 104 kcal/mol. Are there molecules with bonds of hydrogen at much lower bond energies? Try this table: http://srdata.nist.gov/cccbdb/hf0k.asp Methane looks *real* good. I thought of molecules that specifically had the type of bonds known in biochemistry as "hydrogen bonds". These are, in most cases, weaker than covalent bonds. However, the only cases I've seen had an H atom attached to another atom by a hydrogen bond but that H atom was also attached to a second atom by a covalent bond. "Hydrogen bonds" always have the H between two other atoms but is it possible for both of these bonds to be of the "hydrogen bond" type? No. "Hydrogen bonding" is peculiar to hydrogen (because of the small size of the hydrogen atom *once it has already bonded chemically* to a more electronegative atom such as a halogen (fluorine family), chalcogen (oxygen family), or pnictogen (nitrogen family). Unlike other atoms, hydrogen does not have a 'hard nut' of a filled 1S orbital. According to this page hydrogen iodide, HI, with a bond energy of 71 kcal/mole can be decomposed into H and I by uv light at a wavelength of 266 nm: Chem 32 Virtual Manual. http://kalee.tock.com/chem32/the2/26s.html Are there other gases where a single hydrogen atom can be dissociated at a lower energy? Google "hydride photodissociation" Tom Davidson Richmond, VA |
#5
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Monatomic hydrogen as fuel - need a low bond energy to single hydrogen atoms.
Wouter van Marle wrote:
On Wed, 2006-03-22 at 08:25 -0800, Robert Clark wrote: So no, there is no way to have a hydrogen bond without the H atom connected to another atom. Wouter I'll allow it to be attached to another atom. I just want that other bond also to be of the "hydrogen bond" type. Then you're out of luck, as a hydrogen bond is based on the low electronegativity of the H atom, compared to the O atom (the typical companion in a H bond; the other main candidate is N, and I think there will be more), which gives the H atom a somewhat positive charge in the covalent bond. Water is the simplest compound I can think of that has H bonds. In other words: to get a H bond, the H atom in the bond must be bonded covalently to an atom with a high electronegativity, to create a strong dipole. Wouter. Thanks for that. - Bob |
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