Difference between Line Spectrum and Band Spectrum

Key difference: In Physics, a ‘line spectrum’ is a set of discrete wavelengths from gaseous atoms, whereas a ‘band spectrum’ is produced by molecules, which consist of a series of closely spaced lines separated by dark spaces called bands.

Line spectrum is the result of the interactions of the quantum systems and a single photon. These systems are especially associated with atoms and sometimes with the molecules or atomic nuclei. Due to the presence of wavelengths, the spectrum of incandescent solids are considered to be continuous. The spectrum originating from the incandescent gases is called the line spectrum. It is observed that only a few numbers of wavelengths are present in the line spectrum. They appear to be in a series of parallel lines when viewed from a slit. Line spectra are also called atomic spectra, as they originate from the atoms.

Band spectrum is produced by molecules. They are the groups of lines which are closely spaced to one another. In appearance, they are in the form of band, hence the name 'BAND' spectrum. These spectra are characteristics of molecular gases or chemical compounds. When a light is emitted or absorbed by any molecule, it is viewed by a spectroscope with a small dispersion. The spectrum appears to consist of very wide asymmetrical lines called bands. These bands are not equal in intensity, that is, they are increasing (maximum) at one end, while decreasing (minimum) at the other.

In quantum mechanism, the line and band spectrums are the results of emission. The line spectrums are obtained from atoms, while band spectrum is a result of these line spectrums. Band spectrum is obtained from the gaseous molecules. In the line spectrum, the energy levels are distributed, while this is not the case in the band spectrum, wherein the energy levels are in a combined and continuous form.

Comparison between Line Spectrum and Band Spectrum:

 

Line Spectrum

Band Spectrum

Short description

A spectrum of radiation in which the quantity is studied, such as frequency or energy, takes on discrete values.

A spectrum consisting of groups or bands of closely spaced lines in emission or absorption, characteristic of molecular gases and chemical compounds.

Also known as

Atomic spectra.

Molecular spectra.

View

Appears as parallel lines when viewed from a slit.

Appears as continuous form of bands when viewed from a spectroscope.

Nature

They are distinct and unique.

They are continuous and closely spaced with one another.

Image Courtesy: scienceinschool.org, leica-microsystems.com

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