Photosenthesis

[golden_guppy]

WaterFireHO:

I've had a more in depth look into the UV issue. This is what i have so far.

A molecule that has absorbed a quantum of radiation becomes "energy-rich" or excited in the absorption process. Absorption in the wavelength region of interest leads to electronic excitation of the absorber. Absorption at longer wavelengths usually leads to excitation of vibrations or rotations of a molecule in its ground electronic state. Most often, electronic states are involved in photochemical processes because electronically excited species exhibit reactivities distinguishable from those of unexcited species.

Solar radiation, usually UV or visible, but some IR, either fragments molecules into atoms, radicals, and ions, or excites the molecules without chemical change to alter their reactivity.
Planck's law describes the energy of one photon as hν, the light frequency times Planck's constant.
Calculating the energy of one mole L (L = 6.022x1023 molecules or atoms) we find the energy E = Lhν = L h c / λ
= 120,000 / λ [kJ/mole]
= 124 / λ [eV] [Fig. inside cover, Wayne PAP; Fig. 4.1, B&S 86, p.88]
One eV is an energy unit describing the work done by moving 1 mole of electrons through a potential difference of 1 volt and ≅ 100 kJ/mole.
Red light (800 nm) carries 150 kJ/mole and violet (400 nm) carries twice as much energy.
Ultra violet light is divided into sub regions:
near UV 400 - 200 nm
vacuum UV (VUV) 200 - 100 nm
extreme UV (EUV) 100 - 10 nm

Longer wavelength photons tend to excite molecular vibrations, translations, and rotations, but an electronic transition is the spectroscopic step most often associated with photochemical change.

Small, light molecules generally show intense electronic absorption at shorter wavelengths than do more complex compounds

O2 for λ < 200 nm (hence vacuum UV)
H2O for λ < 180 nm
CO2 for λ < 165 nm
N2 and H2 for λ < 100 nm

The first peak in spectrum of of gaseous water is in the Far UV band (166.5 nm) and is due to excitation from the unoccupied pz2-type molecular 1b1 orbital. Absorption of UV close-by (~125 nm), excites the 3a1 orbital leading to dissociation into OH + H (photodissociation). Such dissociation can also be achieved by consecutive absorption of two 266 nm photons.


OK, so with all of that in mind, back to UV light sources.

Mercury gas discharge lamps produce UV at 253.7 nm, and weaker lines in the near-uv and visible, which is too narrow arange to be much use.

Ne, Ar, Kr, Xe discharge lamps : many sharp lines throughout the near-uv to near-IR. Again, not what we're after.

Hydrogen or Deuterium gas discharge lamps produce UV accross the spectrum between 160 - 360 nm. Much more usefull, but not cheap or easy to aquire.

Germicidal Ultraviolet Lamps: Mostly output at 254 nm

UV Pond Clarifiers: Also designed to output at 254 nm. I need to find out the full output spectrum on these bulbs as they may be more wide spectrum than is necessary, which would be good for us.

[AlaskaStar]

[kevinsatterfield]