ATOC 4720 class 25 Radiative transfer The spectrum
- Slides: 8
ATOC 4720 class 25: Radiative transfer • The spectrum of radiation • Absorption and emission of radiation by molecules • Quantitative description of radiation
1. The spectrum of radiation C=300, 000 km/s: Electromagnetic spectrum Visible: 0. 39 -0. 76
Spectrum
2. Absorption and emission of radiation by molecules Molecule energy: kinetic energy & electrostatic potential energy of electrons Lesser energy amount: vibration of atoms (mean position) Rotation of molecule about its center of mass Quantum mechanics: certain configuration of electron orbits are permitted; certain vibrational frequencies and amplitudes, rotational rates Each combination is associated with a particular energy level: sum of 3 types of energy
A molecule transit Level 1 -- Level 2 (absorbing electromagnetic radiation) Level 2 -- Level 1 (drop; emitting radiant energy) Discrete changes in energy levels are allowable: absorption or emission Energy transmitted by electromagnetic radiation exists in discrete units called photons. Energy for a photon of radiation: : frequency
Frequency: the number of waves passing a given point per unit time Wavelength: the distance for a wave to propagate within one period (T) Loner waves, low energy for one photon of radiation; Shorter waves, high energy.
Isolated molecules: discrete energy amounts They can interact only with certain wavelength Radiation. Absorption and emission of an isolated molecule: Line spectrum of a finite number of extremely narrow lines (separated by gaps)
