Oxygen Electronic States, Optical Density - Study Guide | ATMO 689, Study notes of Meteorology

Download Oxygen Electronic States, Optical Density - Study Guide | ATMO 689 and more Study notes Meteorology in PDF only on Docsity! Some important relationships • Optical Density, OD: I = I0 × 10-OD, OD = lC Ø (Lambert-) Beer’s Law I / I0 = transmission l = path length, C = concentration, = (
) = specific absorptivity (or absorption cross section) • Energy of absorption/emission is discrete – E(photon or transition) = h = h c/
(h = Planck’s constant) • Non-electronic transitions require a permanent or inducible dipole (macroscopic analogy: a moving charge creates an alternating electric field that sends out a wave) – N2 and O2 do neither have a permanent dipole (such as H2O), nor an induced dipole  no (vis) IR absorption Dissociation (photolysis energy (has to exceed bonding energy, i.e. hc/ > Ebond) fr om B oe ke r an d va n G ro nd el le : E nv ir on m en ta l P hy si cs O2 UV-light absorption from Finlayson-Pitts and Pitts: Chemistry of the upper and lower Atmosphere O2 NIR-vis absorption from Finlayson-Pitts and Pitts: Chemistry of the upper and lower Atmosphere Relevance for Atmospheric Chemistry • AB + hυ [AB]* ? – [AB]* is an exited (often unstable) state of molecule AB; for an electronic transition due to absorption of UV-vis light, AB* has a different electron configuration than AB (for an infrared absorption AB* ro-vibrates “stronger” than AB) – “ ?” are processes of the following relative importance in the atmosphere: 1. thermal (non-radiative) decay (e.g. greenhouse heating) 2. photolysis (e.g. oxygen or ozone in stratosphere) 3. fluorescence (e.g. NO in thermosphere) 4. phosphorescence (negligible) 5. others (e.g. chemical reaction; negligible)