Difference between revisions of "Bad vibrations"
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== Basic mechanism for the absorption of radiation == | == Basic mechanism for the absorption of radiation == | ||
| − | When radiation (visible light, infra red, ultra violet …) impacts an atom or a molecule, if the frequency of that radiation matches the natural resonant frequency of the molecule energy it is momentarily absorbed, 'exciting' the molecule into a higher energy state. After a short time the same amount of energy is re-radiated and the molecule returns to its normal or 'ground' state. Although the radiation is only 'borrowed' this capture/release is nevertheless an absorption mechanism, because the re-radiation occurs in a '''random''' direction so in the simplified 1-dimensional case there would be a 50% probability the radiation were sent back in the direction it came from. It can be readily understood that for a sufficiently deep and concentrated layer of molecules, this scattering and attenuation could amount to absorption | + | When radiation (visible light, infra red, ultra violet …) impacts an atom or a molecule, if the frequency of that radiation matches the natural resonant frequency of the molecule energy it is momentarily absorbed, 'exciting' the molecule into a higher energy state. After a short time the same amount of energy is re-radiated and the molecule returns to its normal or 'ground' state. Although the radiation is only 'borrowed' this capture/release is nevertheless an absorption mechanism, because the re-radiation occurs in a '''random''' direction so in the simplified 1-dimensional case there would be a 50% probability the radiation were sent back in the direction it came from. It can be readily understood that for a sufficiently deep and concentrated layer of molecules, this scattering and attenuation could amount to absorption |
| − | The three main component gases of earth's atmosphere (diatomic Nitrogen and Oxygen, monatomic Argon) are transparent to heat (infrared) radiation. Or, in terms of the explanation in the previous paragraph, these molecules' bonds are too rigid, too 'highly strung' to respond or resonate to frequencies in the infra-red | + | The three main component gases of earth's atmosphere (diatomic Nitrogen and Oxygen, monatomic Argon) are transparent to heat (infrared) radiation. Or, in terms of the explanation in the previous paragraph, these molecules' bonds are too rigid, too 'highly strung' to respond or resonate to frequencies in the infra-red |
| − | Molecules with three (or more) atoms are different. Additional bonds provide more ways to twist and bend the molecule and in the same way it takes much less energy to bend a ruler than to stretch it, these vibrational modes match specific infra red wavelengths / frequencies. All the 'greenhouse gases' (Carbon dioxide CO | + | Molecules with three (or more) atoms are different. Additional bonds provide more ways to twist and bend the molecule and in the same way it takes much less energy to bend a ruler than to stretch it, these vibrational modes match specific infra red wavelengths / frequencies. All the 'greenhouse gases' (Carbon dioxide CO<sub>2</sub>, Water vapour H<sub>2</sub>O, Methane CH<sub>4</sub>, CFCs etc.) are molecules with three or more atoms |
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| + | == Specific absorption characteristic of CO<sub>2</sub> == | ||
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| + | The CO<sub>2</sub> molecule can stretch symmetrically, stretch asymmetrically and bend parallel or perpendicular to the double bond O=C=O. The wave numbers for these four modes are 2349 cm<sup>-1</sup> 1340 cm<sup>-1</sup> 667 cm<sup>-1</sup> and 667 cm<sup>-1</sup> | ||
Revision as of 11:55, 3 December 2019
Bad vibrations? A brief explanation of the heat trapping properties of CO2
I'm pickin' up good vibrations She's giving me the excitations Brian Wilson / Mike Love / The Beach Boys
Basic mechanism for the absorption of radiation
When radiation (visible light, infra red, ultra violet …) impacts an atom or a molecule, if the frequency of that radiation matches the natural resonant frequency of the molecule energy it is momentarily absorbed, 'exciting' the molecule into a higher energy state. After a short time the same amount of energy is re-radiated and the molecule returns to its normal or 'ground' state. Although the radiation is only 'borrowed' this capture/release is nevertheless an absorption mechanism, because the re-radiation occurs in a random direction so in the simplified 1-dimensional case there would be a 50% probability the radiation were sent back in the direction it came from. It can be readily understood that for a sufficiently deep and concentrated layer of molecules, this scattering and attenuation could amount to absorption
The three main component gases of earth's atmosphere (diatomic Nitrogen and Oxygen, monatomic Argon) are transparent to heat (infrared) radiation. Or, in terms of the explanation in the previous paragraph, these molecules' bonds are too rigid, too 'highly strung' to respond or resonate to frequencies in the infra-red
Molecules with three (or more) atoms are different. Additional bonds provide more ways to twist and bend the molecule and in the same way it takes much less energy to bend a ruler than to stretch it, these vibrational modes match specific infra red wavelengths / frequencies. All the 'greenhouse gases' (Carbon dioxide CO2, Water vapour H2O, Methane CH4, CFCs etc.) are molecules with three or more atoms
Specific absorption characteristic of CO2
The CO2 molecule can stretch symmetrically, stretch asymmetrically and bend parallel or perpendicular to the double bond O=C=O. The wave numbers for these four modes are 2349 cm-1 1340 cm-1 667 cm-1 and 667 cm-1