Full set of Notes with Fill-Ins - San Jose State University

Chem 155 Unit 12 215 of 316IR Spectroscopy is Difficult!• IR beams are invisible to the eye.• IR bands are narrow, so Δλ EFF must be small.• SiO 2 absorbs IR radiation.• Water and other solvents absorb IR radiation.• IR photons are low energy, so they are hard todetect!Why can’t you use a photomultiplier tube in the IR?Infrared radiation has a longer wavelengththan visible radiation:λ IR > λ VIS– so –IR radiation has a lower frequency:ν IR = c/λ IR– so –IR radiation has a lower energy:– so –Photomultiplier tubes don’t work because:E IR = hν IR ,For a PMT to work, the photon energy must be greaterthan the work function of the metal!E ≥ φButE IR ≤ φPage 215 of 316