QUANTIZED ENERGY AND PHOTONS

QUANTIZED ENERGY AND PHOTONS We recognize that electromagnetic radiation also has particle-like properties and can be described in terms of photons, particles of light. 

QUANTIZED ENERGY AND PHOTONS (SECTION 6.2) Planck proposed that the minimum amount of radiant energy that an object can gain or lose is related to the frequency of the radiation E = hv. This smallest quantity is called a quantum of energy. The constant h is called Planck constant/t = 6.626 X 10 J-s. 

The emission spectra of He and reveal transitions at characteristic energies. The emitted photons have different wavelengths and energies because iHe has quantized energy levels that are different from those of l ... 

We have now looked at the way photons are absorbed. Photons of UV and visible light cause electrons to promote between orbitals. Infrared photons have less energy, and are incapable of exciting electrons between orbitals, but they do allow excitation between quantized vibrational levels. The absorption of microwaves, which are less energetic still, effects the excitation between quantized rotational levels. 

In this section, we shall look at the way these various absorptions are analysed by spectroscopists. There are four kinds of quantized energy translational, rotational, vibrational and electronic, so we anticipate four corresponding kinds of spectroscopy. When a photon is absorbed or generated, we must conserve the total angular momentum in the overall process. So we must start by looking at some of the rules that allow for intense UV-visible bands (caused by electronic motion), then look at infrared spectroscopy (which follows vibrational motion) and finally microwave spectroscopy (which looks at rotation). 

Interpretation of (a) absorption and (b) emission spectra of atoms and molecules. The absorption or emission of photons is accompanied by transitions between well-defined, quantized energy levels. 

The procedure, known as second quantization, developed as an essential first step in the formulation of quantum statistical mechanics, which, as in the Boltzmann version, is based on the interaction between particles. In the Schrodinger picture the only particle-like structures are associated with waves in 3N-dimensional configuration space. In the Heisenberg picture particles appear by assumption. Recall, that in order to substantiate the reality of photons, it was necessary to quantize the electromagnetic field as an infinite number of harmonic oscillators. By the same device, quantization of the scalar r/>-field, defined in configuration space, produces an equivalent description of an infinite number of particles in 3-dimensional space [35, 36]. The assumed symmetry of the sub-space in three dimensions decides whether these particles are bosons or fermions. The crucial point is that, with their number indeterminate, the particles cannot be considered individuals [37], but rather as intuitively understandable 3-dimensional waves - (Born) -with a continuous density of energy and momentum - (Heisenberg). 

In spectroscopy it is useful to consider the propagation of electromagnetic radiation in a quantitative manner. Light is transmitted as discrete packets or as a stream of particles of energy called photons. These photons have a specific energy and for spectroscopy are quantized and described by the following equation ... 

In spectroscopy, this quantized energy in the form of photons is applied to biomolecules in a sample and energy is exchanged, and the change in energy level of the biomolecule can be measured. 

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