Higher energy states

Absorption of electromagnetic radiation causes a molecule to be excited from Its most stable state (the ground state) to a higher energy state (an excited state)... 

Nuclear magnetic resonance (NMR) spectroscopy (Section 13 3) A method for structure determination based on the effect of molecular environment on the energy required to promote a given nucleus from a lower energy spin state to a higher energy state... 

The release of a photon when an analyte returns to a lower-energy state from a higher-energy state. 

All forms of spectroscopy require a source of energy. In absorption and scattering spectroscopy this energy is supplied by photons. Emission and luminescence spectroscopy use thermal, radiant (photon), or chemical energy to promote the analyte to a less stable, higher energy state. 

This prescription, which follows directly from the Boltzman distribution, ensures that any update of the system for T > 0 has a finite probability of increasing the energy of the system and thereby of helping the system get out of local minima. The lower the temperature, the less likely are higher energy states as the temperature... 

If the oriented nuclei are now irradiated with electromagnetic radiation of the proper frequency, energy absorption occurs and the lower-energy state "spin-flips" to the higher-energy state. When this spin-flip occurs, the magnetic nuclei are said to be in resonance with the applied radiation—hence the name nuclear magnetic resonance. 

This energy increase can take different forms. It can be added as translational kinetic energy to speed up the movement to and fro of the molecules it can be added to the rotations of the molecules to get them to spin faster it can be added to increase the amplitude of the vibrational oscillations of the molecules and it can be added to excite electrons to higher energy states in the atoms or molecules. Other forms of internal energy are also possible, but the above are the most common. 

When electromagnetic radiation falls on a molecule, the electrons in the molecule can be excited to a higher energy state. Radiation of the frequency v (nu) can raise the energy of the molecule by an amount AE, where... 

Note that we have drawn CP approaching zero as 0. This feature is a general phenomenon, and explained by quantum mechanics. At low temperatures, the energy available is so small that there is not enough to stimulate transitions to higher energy states, so the sample cannot take up energy, and its capacity for heat is zero. 

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