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12 - Molecules. v ’ =3. v ’ =2. v ’ =1. v ’ =0. energy. v ” =2. v ” =1. J ’ s. v ” =0. nuclear separation. Rotational, Vibrational, and Electronic Transitions. Rotational Transitions. Rigid Rotors. wavenumbers. where J=rotational quantum #

germane-atkinson
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  1. 12 - Molecules v’=3 v’=2 v’=1 v’=0 energy v”=2 v”=1 J’s v”=0 nuclear separation Rotational, Vibrational, and Electronic Transitions

  2. Rotational Transitions Rigid Rotors wavenumbers where J=rotational quantum # B=rotational constant for that electronic/vibrational state (In real cases, also need to correct for stretching) For rotational transitions, need a permanent dipole (H2 has none) and the transition rule is: Traditionally, the upper level is labeled J’ and the lower level J’’.

  3. This leads to an emitted spectrum with wavenumbers for a constant value of B for both levels (not always the case). But if for example, we get leading to a series of lines separated by 2B: Example: CO B=1.98 cm-1

  4. H2O Vibrational 3 2 1 0 Example: CO

  5. Combined (rovibrational) 3 2 J’= J’’= v’=1 v’’=0 1 0 3 2 1 0 R branch P branch J’-J’’=+1 J’-J’’=-1 Designation: R(J’’) P(J’’)

  6. Example

  7. Electronic (+ vibrational + rotational)

  8. Examples TiO ZrO in carbon stars

  9. CO Electronic Levels Vibrational Levels Rotational Levels (not shown)

  10. In addition to bound-bound transitions, molecules can be ionized as well as disassociated. Below is a case of radiative dissociation, which we will see again later in the course. 10% 90%

  11. IR Absorption in the Earth’s Atmosphere

  12. Atmospheric Transmission Example - Mauna Kea (13,796 ft = 4,205 m)

  13. Looking upward from two locations on the Earth. The sky is GLOWING where molecules absorb most strongly. From “A First Course in Atmospheric Radiation” by Grant W. Petty

  14. Organics in a young circumstellar disk (Mandell et al. 2012, ApJ, 747, 92)

  15. UV Molecular Transitions in HD 44179 (Sitko et al. 2008, ApJ, 680, 1426)

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