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BEEADTH AND INTENSITY OF AN ABSORPTION BAND. 155

case, the factor ^ in (230), and the factor n in (202) may be con-

sidered as constants. Moreover, in virtue of (201), if n^ is the
frequency for which a ===== 0, we may write for any other value of K
in the interval in question

(»-O- ; (231)

I have written w₀' for the frequency corresponding to a — 0, because
its value

differs from the frequency

«o-l/£
⁰ Y w

of the spectral line of a detached molecule of which we have formerly
spoken. It is only when we may neglect the coefficient a, that the
two may be considered as identical.

The phenomena which the system of molecules produces in the
spectrum of a beam of white light which is sent across it, are as
follows. There is an absorption band in which the place of greatest
darkness corresponds to

n = %'.

The distribution of light is symmetrical on both sides of this point.
As the band has no sharp borders, we cannot ascribe to it a definite
breadth; we can, however, say that it is seen between the places
where a — — vfi and a = -f- v/3, v being a number of moderate
magnitude. Measured by a difference of frequencies, half the width
can tkerefore be represented by «

₀as is seen from (231).

We may add an interesting remark about the intensity of the
absorption. The maximum value of the index of absorption is found
to be

and the formulae (202), (199) and (207) show therefore that the maxi-
mum is the larger, the smaller the resistance, or the longer the time r
during whieh the vibrations ®f the electrons remain undisturbed. This
result, strange at first sight, can be understood, if we take into con-
sideration that the vibrations which are set up in a particle by optical
resonance, so to say, with the incident light, will be sooner or later
converted into an irregular heat motion. It may very well be, that



	BEEADTH AND INTENSITY OF AN ABSORPTION BAND. 155 case, the factor ^ in (230), and the factor n in (202) may be con- sidered as constants. Moreover, in virtue of (201), if n^ is the frequency for which a ===== 0, we may write for any other value of K in the interval in question (»-O- ; (231)

	I have written w₀' for the frequency corresponding to a — 0, because its value

	differs from the frequency «o-l/£ ⁰ Y w of the spectral line of a detached molecule of which we have formerly spoken. It is only when we may neglect the coefficient a, that the two may be considered as identical. The phenomena which the system of molecules produces in the spectrum of a beam of white light which is sent across it, are as follows. There is an absorption band in which the place of greatest darkness corresponds to n = %'. The distribution of light is symmetrical on both sides of this point. As the band has no sharp borders, we cannot ascribe to it a definite breadth; we can, however, say that it is seen between the places where a — — vfi and a = -f- v/3, v being a number of moderate magnitude. Measured by a difference of frequencies, half the width can tkerefore be represented by «

	₀as is seen from (231). We may add an interesting remark about the intensity of the absorption. The maximum value of the index of absorption is found to be

	and the formulae (202), (199) and (207) show therefore that the maxi- mum is the larger, the smaller the resistance, or the longer the time r during whieh the vibrations ®f the electrons remain undisturbed. This result, strange at first sight, can be understood, if we take into con- sideration that the vibrations which are set up in a particle by optical resonance, so to say, with the incident light, will be sooner or later converted into an irregular heat motion. It may very well be, that