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( Molecular structure)
Molecular geometry or molecular structure is the three-dimensional arrangement of the atoms that constitute a molecule. It determines several properties of a substance including its reactivity, polarity, phase of matter, color, magnetism, and biological activity.[1] [2] The mole geometry References for NMR and FRET distances --> [3][4][5] dihedral angles, molecules are thermally excited at room temperature. The lowest excitation vibrational energy in water is the bending mode (about 1600&_160;cm-1). Thus, at room temperature less than 0.07% of all the molecules of a given amount of water will vibrate faster than at absolute zero. As stated above, rotation hardly influences the molecular geometry. But, as a quantum mechanical motion, it is thermally excited at relatively (as compared to vibration) low temperatures. From a classical point of view it can be stated that more molecules rotate faster at higher temperatures, i.e., they have larger angular velocity and angular momentum. In quantum mechanically language more eigenstates of higher angular momentum become thermally populated with rising temperatures. Typical rotational excitation energies are on the order of a few cm-1.
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