General principles of vibrational spectroscopies

Abstract

Atoms in molecules and solids do not remain in fixed relative positions, but vibrate about some mean position. This vibrational motion is quantized and at room temperature, most of the molecules in a given sample are in their lowest vibrational state. Absorption of electromagnetic radiation with the appropriate energy allows the molecules to become excited to a higher vibrational level. The required energy for this transition comes from the infrared region of the electromagnetic light. The absorption of infrared light as a function of wavelength gives rise to an infrared spectrum with specific spectroscopic fingerprints, which can be assigned to certain molecular entities.