Question

How can spectroscopy be used to identify a gas?

Answer 1

Hint : In simpler terms, spectroscopy is the precise study of color as it is generalized from visible light to all bands of the electromagnetic spectrum; indeed, spectroscopy began as a study of the wavelength dependence of the absorption by gas phase matter of visible light dispersed by a prism.

Complete Step By Step Answer:
For over seventy years, infrared spectroscopy has been a workhorse technique for materials analysis in the laboratory. An infrared spectrum is a sample's fingerprint, with absorption peaks corresponding to the frequencies of vibrations between the bonds of the atoms that make up the material. Because each chemical compound is made up of a unique combination of atoms, no two compounds produce the same result.
As a result, infrared spectroscopy can provide a positive identification (qualitative analysis) of the unique composition of a material. Furthermore, the size of the peaks in the infrared spectrum indicates the amount of material present. Infrared spectroscopy is an excellent tool for quantitative analysis when combined with modern software algorithms.
The ability to measure multiple frequencies simultaneously within a single scan is a significant advantage of infrared spectroscopy. Because different IR frequencies cause vibration/rotation of different molecules at different energy levels, this broad spectrum approach provides information for many different types of chemical bonds.
A C=C double bond, for example, is stronger and stiffer than a C-C single bond, so a higher energy input or higher frequency is required to cause a vibration. An H-Cl bond vibrates at a different frequency than an N-O bond. The infrared detector measures the amount of energy that has passed through the sample at each frequency. This yields a spectrum, which is an absorbance plot.

Note :
For several reasons, Fourier transform infrared spectroscopy is preferred over older IR filter instruments or other gas analyzers:
• It is a non-destructive technique that requires little or no sample preparation.
• It is capable of quantifying multiple components over a wide concentration range in a single measurement.
• It provides a precise measurement method with extremely stable calibrations (no need for daily recalibration).
• It can monitor high-speed transient responses as fast as 5 scans/second
• Its sensitivity can be improved by co-adding repeated scans, providing detection limits down to part-per billion for many components