CHM 2354 Lecture Notes - Lecture 17: Rotational Transition, Phosphorescence, Chemiluminescence
25 May 2015
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Document Summary
Fundamentals of spectrophotometry: when a molecule absorbs light it becomes excited. Molecule promoted to a more energetic excited state. There are two possible transitions in excited state: single state electron spins opposed, triplet state electron spin are parallel. In general, triplet state has lower energy than singlet state. Single to triplet transitions has a very low probability. Singlet to triplet transitions are more probable: infrared and microwave radiation. Not energetic enough to induce electronic transitions. Change vibrational, translational, and rotational motion of the molecule. Entire molecule and each atom can move along the x, y, z-axis. When correct wavelength is absorbed: oscillation of the atom vibration is increased in amplitude, molecule rotates or moves (translation) faster. Absorption of photon with sufficient energy to excite an electron will also cause vibrational and rotational transition. There are multiple vibrational and rotational energy (rovibrational) levels associated with each electronic state: excited vibrational and rotational states are lower energy than electronic state.
