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MOLECULAR SPECTROSCOPY
The molecular spectroscopy is the study of the interaction of electromagnetic waves and matter. The
scattering of sun’s rays by raindrops to produce a rainbow and appearance of a colourful spectrum
when a narrow beam of sunlight is passed through a triangular glass prism are the simple examples
where white light is separated into the visible spectrum of primary colours. This visible light is
merely a part of the whole spectrum of electromagnetic radiation, extending from the radio waves
to cosmic rays. All these apparently different forms of electromagnetic radiations travel at the same
velocity but characteristically differ from each other in terms of frequencies and wavelength.
The propagation of these radiations involves both electric and magnetic forces which give rise to
their common class name electromagnetic radiation. In spectroscopy, only the effects associated
with electric component of electromagnetic wave are important. Therefore, the light wave traveling
through space is represented by a sinusoidal trace (figure 1). In this diagram λ is the wavelength and
distance A is known as the maximum amplitude of the wave. Although a wave is frequently
characterized in terms of its wavelength λ, often the terms such as wavenumber ( ν), frequency (ν),
cycles per second (cps) or hertz (Hz) are also used.
The electromagnetic spectrum
The unit commonly used to describe the wavelength is centimeters (cm), the different units are used
to express the wavelengths in different parts of the electromagnetic spectrum. For example, in the
ultraviolet and visible region, the units use are angstrom (Ǻ) and nanometer (nm).
In the infrared region, the commonly used unit is wavenumber (ν), which gives the number of waves
per centimeter. Thus 1 cm = 107 nm = 108 Ǻ 1 Ǻ = 10-1 nm = 10-8 cm.
The four quantities wavelength, wavenumber, frequency and velocity can be related to each other
by following relationships:
wavelength (λ) = 1 / ν = c / ν
Wave-number ( ν) = 1 / λ = ν / c
Frequency (ν) = c / λ = c ν
Velocity (c) = νλ = ν / ν
λ
The wavelength of electromagnetic radiation
MOLECULAR SPECTROSCOPY
The molecular spectroscopy is the study of the interaction of electromagnetic waves and matter. The
scattering of sun’s rays by raindrops to produce a rainbow and appearance of a colourful spectrum
when a narrow beam of sunlight is passed through a triangular glass prism are the simple examples
where white light is separated into the visible spectrum of primary colours. This visible light is
merely a part of the whole spectrum of electromagnetic radiation, extending from the radio waves
to cosmic rays. All these apparently different forms of electromagnetic radiations travel at the same
velocity but characteristically differ from each other in terms of frequencies and wavelength.
The propagation of these radiations involves both electric and magnetic forces which give rise to
their common class name electromagnetic radiation. In spectroscopy, only the effects associated
with electric component of electromagnetic wave are important. Therefore, the light wave traveling
through space is represented by a sinusoidal trace (figure 1). In this diagram λ is the wavelength and
distance A is known as the maximum amplitude of the wave. Although a wave is frequently
characterized in terms of its wavelength λ, often the terms such as wavenumber ( ν), frequency (ν),
cycles per second (cps) or hertz (Hz) are also used.
The electromagnetic spectrum
The unit commonly used to describe the wavelength is centimeters (cm), the different units are used
to express the wavelengths in different parts of the electromagnetic spectrum. For example, in the
ultraviolet and visible region, the units use are angstrom (Ǻ) and nanometer (nm).
In the infrared region, the commonly used unit is wavenumber (ν), which gives the number of waves
per centimeter. Thus 1 cm = 107 nm = 108 Ǻ 1 Ǻ = 10-1 nm = 10-8 cm.
The four quantities wavelength, wavenumber, frequency and velocity can be related to each other
by following relationships:
wavelength (λ) = 1 / ν = c / ν
Wave-number ( ν) = 1 / λ = ν / c
Frequency (ν) = c / λ = c ν
Velocity (c) = νλ = ν / ν
λ
The wavelength of electromagnetic radiation
