- Simon HsiehLv 71 decade agoFavorite Answer
To be "active" means that absorption of a photon to excite the vibration is allowed by the rules of quantum mechanics.
[Aside: the infrared "selection rule" states that for a particular vibrational mode to be observed (active) in the infrared spectrum, the mode must involve a change in the dipole moment of the molecule.]
其中A是 IR inactive
B ,C,D都是IR active
The asymmetric stretch (B) is infrared active because there is a change in the molecular dipole moment during this vibration.
2007-11-06 22:44:25 補充：