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1. General

2. High Energy

3. Medium Energy

4. Low Energy

5. Mass Spectrometry

6. References


This paper was presented for translators at the 36th Annual Conference of the American Translators Association, 1996.

Copyright: American Translators Association. All rights reserved. This document may not be reproduced without the written permission of the American Translators Association. Presented here by permission, and slightly modified for this web page.


Abstract: Analysts use various kinds of interaction between matter and energy to identify elements to identify elements and compounds, and to determine their quantities. This paper is an introduction to the terminology used.

1. General

Spectrometry: measurement of interaction between matter and electromagnetic radiation. (Mass spectrometry does not fit this definition.) Electromagnetic radiation includes the spectrum from ultra-high-frequency radio waves to gamma rays. That covers about six orders of frequency or wavelength. Very rarely if at all would any one person (or even one laboratory) work across the entire range.

Table 1

Range Approximate frequency [sec-1] Approximate wavelength Approximate energy [kcal mol-1]
Microwave 3 · 1011 1 mm 0.03
Infrared (IR) 3 · 10 13 10 µm 3
Near Infrared (NIR) 3 · 1014 1 µm 30
Visible (Vis) 6 · 1014 (green) 500 nm 60
Ultraviolet (UV) 1 · 1015 300 nm 100
Vacuum ultraviolet 3 · 1015 10-100 nm 300
X-ray, gamma ray 3 · 1016 - 3 · 1017 0.1-1 nm
(< 1 - 10 Å)

With this wide range of frequencies/wavelengths, the equipment needed is very different in the different ranges. While we tend to think of optical equipment, that is useful only in the middle of the range, although that will get most of the attention here.

Closely related terms:

Photometry measurements of (visible) light intensity without much regard to color
Spectro- indicates that individual colors/wavelengths/frequencies/energies are considered separately
Spectroscopy has connotation of using an instrument by looking into it, but is commonly used more broadly
Spectrography has connotation of recording on film
Spectrophotometry suggests measurement of visible light, but commonly used also for ultraviolet and infrared
Spectroradiometry usually applied to measurement of intensity of sunlight or other sources
Pyranometry measurement of total radiation from sun and sky
Pyrheliometry measurement of direct radiation from the sun

Spectrometry includes:

A. Emission spectrometry radiation emitted by matter (especially hot matter)
B. Absorption spectrometry radiation absorbed by matter
C. Fluorescence spectrometry radiation absorbed, then, in part, emitted again almost immediately, normally at a longer wavelength (lower energy)

Atoms and molecules have only certain distinct (discrete) amounts of energy (energy levels). Relatively small amount of energy are involved in rotation of molecules, and those measurements are done with far infrared and microwave spectrometry. More energy in involved in vibrations between atoms or groups of atoms (infrared). Still more energy is involved in changes of the electronic structure (visible, ultraviolet, X-ray) and nuclear structure (gamma ray).

Spectrometry is primarily measurement of energy absorbed or emitted as atoms or molecules change from one distinct energy level to another. Each such change involves a fixed amount of energy, which is in a package called a quantum or photon. While these photos can be considered as elemental particles, it is often convenient (or at least usual) to think of them as having wave motion with specific frequencies and wavelengths which are linked to their energies:
  E = hn where E is energy (ergs/atom or molecule)  
      h Planck’s constant (6.62 · 1027erg sec)  
      v is frequency (sec-1)  
Frequency (v) and wavelength (l ) are inversely related:  
  c = lv   l = c/n n = c/l  
where c is the velocity of light in vacuum, about 3·1010 cm sec-1.  
Most of these definitions give inconveniently large or small numbers, so more convenient ones are used in different spectral ranges (see Table 1). Three of them may give trouble:

     millimicron (mµ) = nanometer
     micron (µ) = micrometer
     wave number
     (v with a bar over it)
= wave number, defined as the number of waves in a distance of 1 cm. The wave number is directly proportional to energy/photon, and is used almost solely in the infrared range.


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