Spectroscopy is the study of the absorption, emission, or interaction of electromagnetic radiation by molecules in solid, liquid, and gaseous phases. The spectroscopic studies of vapor, in which the H2O molecules are far apart from each other, reveal a wealth of information about individual H2O molecules. Electromagnetic radiation (light) is the transmission of energy through space via no medium by the oscillation of mutually perpendicular electric and magnetic fields.
The oscillating electromagnetic waves move in a direction perpendicular to both fields at the speed of light (c 2.997925
108 m/s). Max Planck (1858–1947) thought the waves also have particle-like properties except that they have no mass. He further called the light particles photons, meaning bundles of light energy. He assumed the photon’s energy, E, to be proportional to its frequency.
The proportional constant h ( 6.62618
10-34 J/s), now called the Planck constant in his honor, is universal. The validity of this assumption was shown by Albert Einstein’s photoelectric-effect experiment. Max Planck theorized that a bundle of energy converts into a light wave. His theory implies that small systems can be only at certain energy states called energy levels.
Due to quantization, they can gain or lose only specific amounts of energy. Spectroscopy is based on these theories. Water molecules have quantized energy levels for their rotation, vibration, and electronic transitions. Transitions between energy levels result in the emission or absorption of photons. The electromagnetic spectrum has been divided into several regions.
From low energy to high energy, these regions are long radio wave, short radio wave, microwave, infrared (IR), visible, ultraviolet (UV), X rays, and gamma rays. Visible light of various colors is actually a very narrow region within the spectrum. On the other hand, IR and UV regions are very large, and both are often further divided into near and far, or A and B, regions.