Electromagnetic spectrum line spectra

Electromagnetic spectrum, continuous spectrum, line spectrum... 

The positions of lines or bands in the electromagnetic spectrum may be expressed either as wave lengths (X) or as frequencies (v). The units employed in the measurement of wave lengths are ... 

This phosphor has many emission lines in the blue, green, and red areas of the electromagnetic spectrum screens made from it have a whitish appearance... 

Eventually, other series of lines were found in other regions of the electromagnetic spectrum. The Lyman series was observed in the ultraviolet region, whereas the Paschen, Brackett, and Pfund series were observed in the infrared region of the spectrum. All of these lines were observed as they were emitted from excited atoms, so together they constitute the emission spectrum or line spectrum of hydrogen atoms. 

An important observation was that the emission lines are not confined to the narrow visible region of the electromagnetic spectrum. Instrumental detection showed that discrete lines are also present in the infrared and ultraviolet wavelengths, and eventually it showed this in the X-ray region also. It became clear that the wavelength of the line simply corresponded to the energy... 

There are definite distinct lines in the atomic emission spectrum of hydrogen. These lines are seen in the visible part of the spectrum and there is also a series of lines in the infrared and another series in the ultraviolet part of the electromagnetic spectrum. So, although hydrogen is the simplest element with only one electron per atom, its atomic emission spectrum is fairly complicated. 

The use of ultraviolet (UV) spectroscopy for on-line analysis is a relatively recent development. Previously, on-line analysis in the UV-visible (UV-vis) region of the electromagnetic spectrum was limited to visible light applications such as color measurement, or chemical concentration measurements made with filter photometers. Three advances of the past two decades have propelled UV spectroscopy into the realm of on-line measurement and opened up a variety of new applications for both on-line UV and visible spectroscopy. These advances are high-quality UV-grade optical fiber, sensitive and affordable array detectors, and chemometrics. 

Atomic line emissions from Ti in the UV and visible regions of the electromagnetic spectrum (see Figure 8.6). 

Thus, although the colour of sparks is dependent upon flame temperature and may be similar to that of black body radiation, the overall colour effect can include contributions from atomic line emissions, from metals (seen in the UV and visible regions of the electromagnetic spectrum), from band emissions from excited oxide molecules (seen in the UV, visible and IR regions) and from continuum hot body radiation and other luminescence effects. So far as black body radiation is concerned, the colour is known to change from red (500 °C glowing cooker... 

Not really a spectroscopic technique in that the line spectrum produced does not arise from quantization of electromagnetic radiation. Of specialized interest only not further discussed here. 

Other spectral regions are also important because the detection and quantification of small concentrations of labile molecular, free radical, and atomic species of tropospheric interest both in laboratory studies and in ambient air are based on a variety of spectroscopic techniques that cover a wide range of the electromagnetic spectrum. For example, the relevant region for infrared spectroscopy of stable molecules is generally from 500 to 4000 cm-1 (20-2.5 /Am), whereas the detection of atoms and free radicals by resonance fluorescence employs radiation down to 121.6 nm, the Lyman a line of the H atom. 

Consider the line frequencies of an electronic transition. The quantity T e Tf is some constant for the pair of electronic states involved, and simply determines which region of the electromagnetic spectrum the transition falls. The positions of the vibrational bands are determined by... 

Figure 23-1 A part of the electromagnetic spectrum. The letters Vy By G, Y, O, R over the visible part of the spectrum refer to the colors of the light. The position marked "Ka line of Cu" is the wavelength of X-rays and most widely employed in X-ray diffraction studies of proteins and other organic materials.

ABSORPTION BAND. A range of wavelengths (or frequencies) in the electromagnetic spectrum within which radiant energy is absorbed by a substance. When the absorbing substance is a polyatomic gas, an absorption band actually is composed of a group of discrete absorption lines, which appear to overlap. Each line is associated with a particular mode of vibration or rotation induced in a gas molecule by the incident radiation. The absorption bands of oxygen and ozone are often referred to in the literature of atmospheric physics. 

In line with current practice in the literature, we shall mainly use the nanometer (nm) as the unit of wavelength. One nanometer is equal to 10"7 cm. Not long ago the millimicron (m/x) was most frequently used by organic photochemists. One millimicron is exactly equal to one nanometer. Other units often seen are the angstrom (A), which is equal to 10"8 cm, and the wave number, v, which is equal to 1/A (the units of v therefore depend on the unit of A). The region of the electromagnetic spectrum that brings about controlled electronic excitation and thus is of interest to photochemists is approximately from 200 to 700 nm (2000 to 7000 A). 

Subsequent to the discovery of the Balmer series of lines in the visible region of the electromagnetic spectrum, it was found that many other spectral lines are also present in nonvisible regions of the electromagnetic spectrum. Hydrogen, for example, shows a series of spectral lines called the Lyman series in the ultraviolet region and still other series (the Paschen, Brackett, and Pfund series) in the infrared region. 

PROBLEM 5.4 The Balmer equation can be extended beyond the visible portion of the electromagnetic spectrum to include lines in the ultraviolet. What is the wavelength (in nanometers) of ultraviolet light in the Balmer series corresponding to a value of n = 7 ... 

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