preface to fifteenth edition

SPECTROSCOPY 7.39
In terms of m , the wavenumber of maximum emission:
3.48T
m
Another useful version is hvm
5kT, where k is the Boltzmann constant.
Stefan’s law states that the total energy J radiated by a blackbody per unit time and area (power
per unit area) varies as the fourth power of the absolute temperature:
J aT 4
8 2 4
where a is a constant whose value is 5.67 10 W·m ·K .
The relationshipbetween the voltage of an X-ray tube (or other energy source), in volts, and the
wavelength is given by the Duane-Hunt equation:
hc 12 398
eV V
where the wavelength is expressed in angstrom units.
7.4.1.2 Laws of Photometry. The time rate at which energy is transported in a beam of radiant
energy is denoted by the symbol P 0 for the incident beam, and by P for the quantity remaining
unabsorbed after passage through a sample or container. The ratio of radiant power transmitted by
the sample to the radiant power incident on the sample is the transmittance T:
P
T
P0
The logarithm (base 10) of the reciprocal of the transmittance is the absorbance A:
1
A log T log T
When a beam of monochromatic light, previously rendered plane parallel, enters an absorbing
medium at right angles to the plane-parallel surfaces of the medium, the rate of decrease in radiant
power with the length of light path (cuvette interior) b, or with the concentration of absorbing material
C (in grams per liter) will follow the exponential progression, often referred to as Beer’s law:
abC
T 10 or A abC
where a is the absorptivity of the component of interest in the solution. When C is expressed in
moles per liter,
bC
T 10 or A bC
where is the molar absorptivity.
The total fluorescence (or phosphorescence) intensity is proportional to the quanta of light absorbed,
P0
P, and to the efficiency , which is the ratio of quanta absorbed to quanta emitted:
bC
F (P0 P) P0 (1 e )
When the terms bC is not greater than 0.05 (or 0.01 in phosphorescence),
F kP bC 0