Electronics infrared radiation

It is well known that y or X photons have energies suitable for excitation of inner or core electrons. We can use ultraviolet and visible radiation to initiate chemical reactions (photochemistry, valence electron). Infrared radiation excites bond vibrations only, whereas microwaves excite molecular rotation. 

In absorption spectroscopy a beam of electromagnetic radiation passes through a sample. Much of the radiation is transmitted without a loss in intensity. At selected frequencies, however, the radiation s intensity is attenuated. This process of attenuation is called absorption. Two general requirements must be met if an analyte is to absorb electromagnetic radiation. The first requirement is that there must be a mechanism by which the radiation s electric field or magnetic field interacts with the analyte. For ultraviolet and visible radiation, this interaction involves the electronic energy of valence electrons. A chemical bond s vibrational energy is altered by the absorbance of infrared radiation. A more detailed treatment of this interaction, and its importance in deter-... 

As with electronic spectra, the use of infrared spectra for quantitative determinations depends upon the measurement of the intensity of either the transmission or absorption of the infrared radiation at a specific wavelength, usually the maximum of a strong, sharp, narrow, well-resolved absorption band. Most organic compounds will possess several peaks in their spectra which satisfy these criteria and which can be used so long as there is no substantial overlap with the absorption peaks from other substances in the sample matrix. 

Microwave measurements are typically performed at frequencies between 8 and 40 Gc/s. The sensitivity with which photogenerated charge carriers can be detected in materials by microwave conductivity measurements depends on the conductivity of the materials, but it can be very high. It has been estimated that 109-1010 electronic charge carriers per cubic centimeter can be detected. Infrared radiation can, of course, also be used to detect and measure free electronic charge carriers. The sensitivity for such measurements, however, is several orders of magnitude less and has been estimated to be around 1015 electronic charge carriers per cubic centimeter.1 Microwave techniques, therefore, promise much more sensitive access to electrochemical mechanisms. 

Luminescence can be defined as the emission of light (intended in the broader sense of ultraviolet, visible, or near infrared radiation) by electronic excited states of atoms or molecules. Luminescence is an important phenomenon from a basic viewpoint (e.g., for monitoring excited state behavior) [1] as well as for applications (lasers, displays, sensors, etc.) [2,3]. 

Chemiluminescence (CL) is the emission of the electromagnetic (ultraviolet, visible, or near infrared) radiation by molecules or atoms resulting from a transition from an electronically excited state to a lower state (usually the ground state) in which the excited state is produced in a chemical reaction. The CL phenomenon is relatively uncommon because, in most chemical reactions, excited molecules... 

Infrared radiation has a very low energy and cannot eject electrons from most common photoemissive surfaces. The initial infrared sensors were temperature-sensing devices. Thermocouples and thermistors are forms of bolometers used for detecting infrared radiation. 

Fourier-transform infrared (FTIR) spectroscopy Spectroscopy based on excitation of vibrational modes of chemical bonds in a molecule. The energy of the infrared radiation absorbed is expressed in inverse centimeters (cm ), which represents a frequency unit. For transition-metal complexes, the ligands -C N and -C=0 have characteristic absorption bands at unusually high frequencies, so that they are easily distinguished from other bonds. The position of these bonds depends on the distribution of electron density between the metal and the ligand an increase of charge density at the metal results in a shift of the bands to lower frequencies. 

Over the past decade two forms of vibrational optical activity have become established. One is called vibrational circular dichroism (VCD), the extension of electronic circular dichroism into the infrared vibrational region of the spec-tram. The first measurements of VCD were reported by George Holzwarth and co-workers at the University of Chicago in 1973 for crystals (3) and 1974 for neat liquids (4). In VCD one measures the small difference in the absorption of a sample for left versus right circularly polarized incident infrared radiation. The early stages of the development of VCD have been reviewed from several perspectives (5-8). 

A photoconductive detector is a semiconductor whose conductivity increases when infrared radiation excites electrons from the valence band to the conduction band. Photovoltaic detectors contain pn junctions, across which an electric field exists. Absorption of infrared radiation creates electrons and holes, which are attracted to opposite sides of the junction and which change the voltage across the junction. Mercury cadmium telluride (Hg,. Cd/Te, 0 < x < 1) is a detector material whose sensitivity to different wavelengths is affected by the stoichiome-try coefficient, x. Photoconductive and photovoltaic devices can be cooled to 77 K (liquid nitrogen temperature) to reduce thermal electric noise by more than an order of magnitude. 

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