Units, wavelength

The energy of electronic transitions corresponds to light in the visible, UV, and far-UV regions of the spectrum (Fig. 7.1). Absorption positions are normally expressed in wavelength units, usually nanometers (nm). If a compound absorbs in... 

TheNd + ion shows several absorption lines of different widths in crystals. One of the absorption lines of Nd + ion in yttrium vanadate (YVO4) peaks at 809 nm and presents a natural broadening at 2 K with a full width at half maximum of (A v)nat =18 GHz. Estimate (a) The natural broadeiung in the wavelengths units (nm) and (b) the lifetime of the excited state. 

Implementing this level of automation intelligence has been the most difficult to realize within manufacturing industries. That is, while automation controls integration of simple univariate instruments (e.g., a hlter photometer) is seamless, it is much more problematic for multivariate or spectral instruments. This is due to the tower of babble problem with various process spectroscopic instraments across process instrument manufactures. That is, the communications protocols, wavelength units and hie formats are far from standardized across spectral instruments, even within a particular class of techniques such as vibrational spectroscopy. Several information technology (IT) and automation companies have recently attempted to develop commercialized solutions to address this complex problem, but the effectiveness of these solutions has yet to be determined and reported. 

The position of an absorption band is measured on a wavelength scale which may be calibrated in angstroms (A), nanometre (nm) or micron (pm) units. Angstrom units were most commonly used in early mineral spectroscopy literature, including the first edition of this book. However, in current spectral mineralogy research, absorption spectra are often plotted on nanometre scales, whereas micron units are commonly employed in reflectance spectra and remote-sensing applications (chapter 10). The relationship between these wavelength units is... 

Some spectra are recorded on a wavenumber scale, which is inversely proportional to wavelength. The most common wavenumber unit is the reciprocal centimetre, which is related to wavelength units as follows ... 

Wavenumber (Section 13.4) The reciprocal of wavelength (units are cm-1) used in infrared spectroscopy. 

FOM = number of photons/unit time/solid angle/unit wavelength/unit circulating current (3-1)... 

Table 24-1 gives the wavelength units for several spectral regions. 

The effective bandwidth of a wavelength selector is the width of the band of radiation in wavelength units at half-peak height. 

The wavelength unit preferred for the ultraviolet and visible regions of the spec-tram is nanometer, while the unit micrometer is preferred for the infrared region. In this last case, wavenumbers are often used in place of wavelength, and the unit is cm . See below for a definition of the ultraviolet, visible, and infrared regions of the spectrum. ... 

First, we will examine some of the basic features of an infrared spectrum. Early infrared instruments recorded percentage transmittance over a linear wavelength range. It is now unusual to use wavelength for routine samples and inverse wavelength units are used. This is the wavenumber scale, and the units used are cm"i. The output from the instrument is referred to as a spectrum. Most commercial instruments present the spectrum with the wavenumber decreasing from left to right... 

The Doppler width of a spectral line is given by the well-known relation AA = (7.162 x lO ) AT where wavelength units are in Angstroms, temperature is in degrees Kelvin and M is the atomic mass. This relation between four variables is amenable to representation by a nomograph, which does not appear to have been constructed but which would seem to be of practical value. Therefore such a nomograph is presented here. Its construction is briefly described so that the reader who has not made a plot of this type may follow the steps. 

---