the guy Posted November 7, 2009 Share Posted November 7, 2009 does UV radiation have the ability to break up water molecules? if so please specify the wavelength Link to comment Share on other sites More sharing options...
swansont Posted November 7, 2009 Share Posted November 7, 2009 Electrolysis takes about 1.25 eV wavelength = hc/E Link to comment Share on other sites More sharing options...
the guy Posted November 7, 2009 Author Share Posted November 7, 2009 ok, what is hc and what is E? Link to comment Share on other sites More sharing options...
swansont Posted November 7, 2009 Share Posted November 7, 2009 h is Planck's constant, c is the speed of light and E is energy hc=1240 eV nm So that means the wavelength needs to be 1000 nm or shorter, which covers all the visible spectrum and gets you into the near-IR. This doesn't seem right — the electrolysis energy includes breaking off the Oxygen but also forming an O2 molecule, and happens in the presence of other molecules. This calculation http://answers.yahoo.com/question/index?qid=20081107045616AAfd4jT says that you need about 5.25 eV to split off a hydrogen, which happens at 237 nm or shorter Link to comment Share on other sites More sharing options...
John Cuthber Posted November 7, 2009 Share Posted November 7, 2009 Water is transparent to UV light sown to at least 190nM so that calculation is wrong. Link to comment Share on other sites More sharing options...
swansont Posted November 8, 2009 Share Posted November 8, 2009 Water is transparent to UV light sown to at least 190nM so that calculation is wrong. Vapor or liquid? AFAIK the liquid spectrum shifts the resonances to longer wavelengths Link to comment Share on other sites More sharing options...
John Cuthber Posted November 8, 2009 Share Posted November 8, 2009 I found some data. In the gas phase the absorbtion maximum is at about 167nM I can't find any data for the liquid but it's certainly below the UV cutoff of most instruments because air absorbs from about 190 nM. Link to comment Share on other sites More sharing options...
the guy Posted November 9, 2009 Author Share Posted November 9, 2009 so anything under 190nm will do? Link to comment Share on other sites More sharing options...
John Cuthber Posted November 9, 2009 Share Posted November 9, 2009 In principle yes. the yeild will get better as you go towards 167nm. Have fun trying to set this up; air is opaque to those wavelengths. Link to comment Share on other sites More sharing options...
the guy Posted November 9, 2009 Author Share Posted November 9, 2009 why is air opaque to those wavelengths? Link to comment Share on other sites More sharing options...
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