The key difference between atomic spectroscopy and molecular spectroscopy is that the atomic spectroscopy refers to the study of the electromagnetic radiation absorbed and emitted by atoms whereas the molecular spectroscopy refers to the study of the electromagnetic radiation absorbed and emitted by molecules.

There are many different types of spectroscopy, but the most common types used for chemical analysis include atomic spectroscopy, ultraviolet and visible spectroscopy, infrared spectroscopy, Raman spectroscopy and nuclear magnetic resonance.

Spectroscopy Types

• X-ray spectroscopy. In X-ray crystallography, X-rays of sufficient energy are used to excite the inner shell electrons in the atoms of a sample.
• Flame spectroscopy.
• AE spectroscopy.
• AA spectroscopy.
• Spark or arc (emission) spectroscopy.
• Visible and UV spectroscopy.
• IR and NIR spectroscopy.
• NMR.

Molecular spectroscopy involves the interaction of electromagnetic radiation with materials in order to produce an absorption pattern (i.e. a spectrum) from which structural or compositional information can be deduced.

The basis of molecular spectroscopy is the excitation of atoms and molecules by photons. Atoms and molecules excited from the ground state undergo either resonant vibrations or electronic transitions, depending on the nature of the induced quantum mechanical changes.

The basic principle shared by all spectroscopic techniques is to shine a beam of electromagnetic radiation onto a sample, and observe how it responds to such a stimulus. The response is usually recorded as a function of radiation wavelength.

Spectroscopy is used as a tool for studying the structures of atoms and molecules. The large number of wavelengths emitted by these systems makes it possible to investigate their structures in detail, including the electron configurations of ground and various excited states.

Raman spectroscopy has a number of advantages over other analysis techniques.

• Can be used with solids, liquids or gases.
• No sample preparation needed.
• Non-destructive.
• No vacuum needed unlike some techniques, which saves on expensive vacuum equipment.
• Short time scale.

Spectroscopy is also used in astronomy and remote sensing on Earth. Most research telescopes have spectrographs. The measured spectra are used to determine the chemical composition and physical properties of astronomical objects (such as their temperature and velocity).

Some practical ways we use spectroscopy include: We can use the unique spectra to identify the chemical makeup, and temperature and velocity of objects in space. For metabolite screening and analysing, and improving the structure of drugs.

The systematic attribution of spectra to chemical elements began in the 1860s with the work of German physicists Robert Bunsen and Gustav Kirchhoff, who found that Fraunhofer lines correspond to emission spectral lines observed in laboratory light sources.

Joseph von Fraunhofer

Ultraviolet-visible (UV-Vis) spectroscopy is a widely used technique in many areas of science ranging from bacterial culturing, drug identification and nucleic acid purity checks and quantitation, to quality control in the beverage industry and chemical research.

Explanation: Spectroscopy could be used as a qualitative analysis technique by monitoring a particular characteristics of products or reactants in a chemical reaction.

NMR spectroscopy is the use of NMR phenomena to study the physical, chemical, and biological properties of matter. Chemists use it to determine molecular identity and structure. Medical practitioners employ magnetic resonance imaging (MRI), a multidimensional NMR imaging technique, for diagnostic purposes.

The field of life sciences typically applies UV/VIS spectrophotometry in the analysis of nucleic acids, proteins and bacterial cell cultures. Concentration determination of proteins by direct measurement or colorimetric assays, study of enzymatic reactions, and monitoring growth curves of bacterial cell suspensions.

The UV range extends from 100–400 nm, and the visible spectrum ranges from 400–700 nm. However, most spectrophotometers do not operate in the deep UV range of 100–200 nm, as light sources in this range are expensive.

The main disadvantage of using a UV-VIS spectrometer is the time it takes to prepare to use one. With UV-VIS spectrometers, setup is key. You must clear the area of any outside light, electronic noise, or other outside contaminants that could interfere with the spectrometer’s reading.

deviations in absorptivity coefficients at high concentrations (>0.01M) due to electrostatic interactions between molecules in close proximity. scattering of light due to particulates in the sample. fluoresecence or phosphorescence of the sample. changes in refractive index at high analyte concentration.

The advantage of an Ultraviolet – Visible Light Spectrophotometer (UV-Vis spectrophotometer) is its quick analysis ability and easy to use. In astronomy research, an UV / Vis spectrophotometer helps the scientists to analyze the galaxies, neutron stars, and other celestial objects.

This last is particularly important, as spectrometers are very sensitive to changes in temperature, which can throw them out of calibration. Amongst the disadvantages is the loss of light in the fibers. The recorded spectrum is multiple images of the spectrometer’s slit, each at a different wavelength.

The sampling chamber of an FTIR can present some limitations due to its relatively small size. Mounted pieces can obstruct the IR beam. Usually, only small items as rings can be tested. Several materials completely absorb Infrared radiation; consequently, it may be impossible to get a reliable result.

Organic compounds, especially those with a high degree of conjugation, also absorb light in the UV or visible regions of the electromagnetic spectrum. Solvent polarity and pH can affect the absorption spectrum of an organic compound.

In the absorbance range encompassing 0.2 to 0.8, the photometric accuracy of a reference material established by a standardising laboratory shall certify a value in this range with a tolerance of ± 0.001 A at the 0.2 A level, and ± 0.004 A at 0.8 A.

Deuterium lamps are always used with a Tungsten halogen lamp to allow measurements to be performed in both the UV and visible regions. Also known as quartz Iodine lamps, these measure most effectively in the visible region from 320 – 1100 nm.

100-400 nm

Identification of chromophores: 1. Spectrum having a band near 300 mµ may possess two or three conjugated units. 2. Absorption bands near 270-350 mµ with very low intensity ɛmax 10-100 are because of n-π* transitions of carbonyl group.

Common examples include retinal (used in the eye to detect light), various food colorings, fabric dyes (azo compounds), pH indicators, lycopene, β-carotene, and anthocyanins.

Examples include the hydroxyl group (−OH), the amino group (−NH2), the aldehyde group (−CHO), and the methyl mercaptan group (−SCH3). An auxochrome is a functional group of atoms with one or more lone pairs of electrons when attached to a chromophore, alters both the wavelength and intensity of absorption.