Look into the spectrum
through spectroscopy
"What we are nowadays hearing of the language of spectra is a true 'music of the spheres' in order and harmony that becomes ever more perfect despite the manifold variety. All integral laws of spectral lines and of atomic theory spring originally from the quantum theory. It is the mysterious organon on which Nature plays her music of the spectra, and according to the rhythm of which she regulates the structure of the atoms and nuclei."
- Arnold Sommerfeld, Atombau und Spektrallinien
Imagine you have a magical pair of glasses that allow you to see things in a whole new light—literally! Spectroscopy is like those glasses but for scientists. Instead of helping you see hidden worlds, spectroscopy helps scientists see hidden details about the stuff around us by using light beyond the power of our naked eye to comprehend. You know how when you look at a rainbow, you see all those different colors? Well, light is made up of lots of different colors (wavelength), and each color has its own special "fingerprint" that can tell us about what it's made of. Spectroscopy is like taking a close look at those fingerprints to figure out what's in the things around us. Together, they form a symphony of energy, each wavelength playing its part in the cosmic melody of existence. Within the Electromagnetic Spectrum lies the key to understanding the universe and unlocking its infinite wonders.
1. A picture of sunlight at a particular (random) angle. Due to the angle and some imperfections in the mobile camera, the sunlight splits into different colors which is the essence of spectroscopy.
2. Splitting of light in a diffracting grating which splits the light in a more organized manner. The diffracting grating is an important tool in spectroscopy. Which gives us a goos spectrum of white light.
3. The sunlight is reflected by a diamond-like crystal which produces a unique color. This is not essentially a useful way to understand spectroscopy but understanding the physics behind it is useful to understand spectroscopy.
(Images taken by John and are not edited or color corrected)
A spectrum refers to a range or continuum of something, typically ordered by some characteristic quality. In physics, the electromagnetic spectrum encompasses the range of all possible frequencies of electromagnetic radiation, including visible light, radio waves, microwaves, infrared, ultraviolet, X-rays, and gamma rays. The visible light spectrum, for instance, includes all the colors of light that can be seen by the human eye, from red to violet.
The nature of the electromagnetic spectrum is that it is always in a state of interaction with matter. Actually, we can confirm the presence of spectrum only through interaction with matter. We can use this interacting nature of the electromagnetic spectrum to look out for what is around us and understand nature. This technique which is used to study the spectrum is called Spectroscopy. Through spectroscopic techniques, people can analyze how light is absorbed, emitted, or scattered by substances, allowing them to infer characteristics such as composition, structure, and behavior.
Figure elucidating the interaction of the electromagnetic wave with the matter in a technical way
Click the image to view better
Spectroscopy enables us to explore and understand the spectrum by examining how different materials interact with electromagnetic radiation. By analyzing the patterns and characteristics of the spectrum, spectroscopy provides valuable insights into the nature of matter and its interactions with light. Thus, spectroscopy and spectrum are intimately linked, with spectroscopy serving as the primary tool for studying and interpreting the spectrum
Note on spectrum
The concept of the electromagnetic spectrum has evolved over centuries, beginning with Isaac Newton's experiments on visible light in the 17th century and progressing through subsequent discoveries by scientists such as Thomas Young and Augustin-Jean Fresnel, who revealed light's wave nature. James Clerk Maxwell's equations in the 19th century provided a theoretical framework for understanding electromagnetic radiation, while the study of spectroscopy, pioneered by Joseph von Fraunhofer and Gustav Kirchhoff, shed light on the interaction between light and matter. The 20th and 21st centuries saw advancements in technology enabling the exploration of regions beyond the visible spectrum, leading to the discovery and utilization of radio waves, microwaves, infrared radiation, ultraviolet radiation, X-rays, and gamma rays. Today, the electromagnetic spectrum encompasses a wide range of frequencies or wavelengths, each playing a crucial role in scientific research, technology development, and everyday applications, driving innovation and deepening our understanding of the universe.
The theoretical framework of spectra
The theoretical framework of the electromagnetic spectrum is based on the principles of electromagnetism and quantum mechanics. Electromagnetism provides a fundamental understanding of how electric and magnetic fields interact and propagate through space. These equations describe how electromagnetic waves, including light, propagate at the speed of light and carry energy and momentum. Quantum mechanics further refined our understanding of the electromagnetic spectrum by introducing the concept of quantized energy levels. According to quantum mechanics, energy is not continuously distributed but exists in discrete packets or quanta. This concept explains phenomena such as the discrete spectral lines observed in spectroscopy, where atoms and molecules absorb or emit light at specific frequencies corresponding to the energy differences between their quantized energy levels.
How the electromagnetic spectrum is produced?
The electromagnetic spectrum is produced by the emission, absorption, and scattering of electromagnetic radiation by matter, ranging from subatomic particles to astronomical objects.
Emission: Atoms, molecules, and other particles can emit electromagnetic radiation when they undergo transitions between energy levels. For example, when an electron in an atom moves from a higher energy level to a lower one, it emits a photon of electromagnetic radiation. The frequency (or wavelength) of the emitted radiation depends on the energy difference between the initial and final energy levels, according to the equation ΔE=hν, where ΔE is energy, ℎ h is Planck's constant, and ν is frequency. This emitted radiation contributes to the electromagnetic spectrum.
Different ways of obtaining electromagnetic spectra in a lab.
Absorption: Conversely, matter can absorb electromagnetic radiation when it interacts with photons. If the energy of a photon matches the energy needed to promote an electron from a lower energy level to a higher one, the photon will be absorbed, and the electron will transition to a higher energy level. The absorbed radiation is typically in specific frequency ranges corresponding to the energy differences between the atomic or molecular energy levels involved. This absorption leads to dark absorption lines in the electromagnetic spectrum, where certain frequencies of light are missing due to absorption by specific substances.
Scattering: When electromagnetic radiation interacts with particles or surfaces, it can be scattered in different directions. The scattered radiation contributes to the overall electromagnetic spectrum, often with no distinct pattern. However, certain types of scattering, such as Rayleigh scattering, are wavelength-dependent and can result in phenomena like the blue color of the sky.
Synchrotron Radiation: In some cases, highly energetic particles moving through magnetic fields, such as those in synchrotron accelerators or astrophysical environments, can emit synchrotron radiation. This radiation spans a wide range of frequencies and contributes to the electromagnetic spectrum.
These processes result in a continuous range of frequencies or wavelengths, from radio waves to gamma rays, that make up the electromagnetic spectrum.
Emission spectra of various elements in the periodic table in the visible region. This means that these elements when heated produce a light that contains this spectrum. If you see the emission spectra of Tungsten (W) and Neon (Ne) you can see the presence of a complete spectrum i.e. all the visible colors are visible, This is the reason these materials are used in lighting applications.
Source : THE Elements A Visual Exploration of Every Known Atom in the Universe. Photographs by Theodore Gray and Nick Mann
What is spectroscopy?
Spectroscopy is a scientific technique used to study the interaction between matter and electromagnetic radiation. It involves analyzing how materials absorb, emit, or scatter light at different wavelengths or frequencies. By examining the unique patterns of light absorbed or emitted by a substance, spectroscopy provides valuable information about its composition, structure, and properties. Some common spectroscopic methods include infrared spectroscopy, ultraviolet-visible spectroscopy, nuclear magnetic resonance spectroscopy, and mass spectrometry.
In spectroscopy, several fundamental equations are essential for describing the interaction between electromagnetic radiation and matter.
- The Beer-Lambert Law establishes a relationship between the absorbance of light by a sample and the concentration of the absorbing species, defined by the molar absorptivity, concentration, and path length of the sample.
- The Planck-Einstein Relation relates the energy of a photon to its frequency or wavelength, providing a basis for understanding the quantized nature of electromagnetic radiation.
- The Rydberg Formula describes the wavelengths of spectral lines emitted or absorbed by hydrogen-like atoms, aiding in the analysis of atomic spectra.
Let's become a spectroscopist
First, Using a CD as a diffraction grating to split white light and analyze it is a simple yet effective way to demonstrate spectroscopy. CDs, with their closely spaced tracks of pits and lands, act as diffraction gratings when illuminated with white light. When white light is directed onto the surface of a CD, the grooves on the CD surface diffract the light, causing it to spread out into its component colors. This process is similar to how a prism splits white light into a rainbow of colors. Each color in the spectrum corresponds to a specific wavelength of light. By observing the pattern of colors produced by the diffracted light from the CD, one can analyze the spectrum of the light source. This spectrum reveals information about the composition of the light source, as different materials emit or absorb light at specific wavelengths.
1. The spectrum of white light was obtained using the above-mentioned way.
2. The spectrum of green led. As you can see green LED is partially composed of red and blue lights other than green light which is evident by comparing the spectra with the graph in 7.
3. The spectra of red LED. As you can see it is partially composed of yellow light i.e. the red light for the LED splits into red and yellow-orange colors.
4. The spectrum of blue LED. As you can see the blue LED spectra split into indigo and violet.
5. The clear spectrum of which light.
6. The graph showing the composition of different LEDs and compare it with white light and a distant astronomical object (DOI:10.3762/bjoc.12.170)
(1-5 are taken using a mobile camera and they are un-edited images)
Second, In this experiment, various concentrations of a colored liquid are prepared, with each solution having a different level of light absorption due to the presence of colored molecules. To perform the experiment, a light source, such as a smartphone flashlight, is directed through each solution. The color picker app is then used to measure the intensity of light transmitted through the liquid. By comparing the intensity of the transmitted light for each concentration, one can determine the absorbance of the liquid at specific wavelengths. According to the Beer-Lambert Law, absorbance is directly proportional to the concentration of the absorbing species and the path length of the sample. Therefore, as the concentration of the colored molecules in the liquid increases, so does the absorbance of the solution. By plotting the absorbance values against the concentration of the colored liquid, a linear relationship should be observed, confirming the validity of the Beer-Lambert Law.
UV/VIS absorbance spectrum of sucrose solutions over 10 mm path length. As you can see for higher conc. the absorption is high. It is because there are more number of molecules when the concentration is higher so the incident light will interact with more molecules hence the absorption is greater.
Source: doi: 10.3390/s8010010 Cantilever Micro-rheometer for the Characterization of Sugar Solutions
Beginner course in analyzing spectra
UV spectroscopy, also known as ultraviolet-visible (UV-Vis) spectroscopy, is a technique used to measure the absorption of ultraviolet and visible light by molecules in solution. UV-Vis spectroscopy relies on the fact that molecules absorb light at specific wavelengths corresponding to transitions of electrons between different energy levels. The absorption of light causes the electrons to move to higher energy levels, which results in a decrease in the intensity of the transmitted light. The absorption spectrum obtained shows peaks and troughs corresponding to the wavelengths at which the molecule absorbs light.
The raw UV spectra of tea samples in the wavelength range of 400–2498 nm are plotted in Figure.
Visible and near-infrared spectra of tea samples.
(From the article "Nondestructive monitoring of polyphenols and caffeine during green tea processing using UVVis-NIR spectroscopy")
Source: DOI:10.1002/fsn3.1861
The absorption peaks at 480 nm and 670 nm were located in the visible region of the spectra (400–800 nm). It proved that the tea leaves mostly absorb light in the visible spectral range (blue-violet (455–492 nm) and red (622–770 nm)) while green light absorption (500–560 nm) is too low, so this is the reason the tea leaves look green.
The absorption spectra of water showers that the water doesn't have any absorption peaks in the visible light region so the water is transparent to visible light.
Absorption spectra of Water for a wide range of incident electromagnetic waves.
Nuclear Magnetic Resonance (NMR) spectroscopy is a powerful technique for studying molecule structure and dynamics. It exploits the magnetic properties of atomic nuclei, revealing details about their arrangement and chemical environment. By subjecting samples to radiofrequency radiation in a strong magnetic field, NMR spectroscopy generates spectra with peaks corresponding to specific nuclei types. This information aids in identifying compounds and understanding molecular interactions.
When peanuts are used as adulterants, there is an additional risk of potential health hazard to consumers due to allergy-induced anaphylaxis. Peanuts can be used as an adulterant in powdered hazelnuts, almonds, and walnuts. The close inspection of NMR spectra of various powders can reveal the peanut as an adulterant in these products.
H NMR spectra obtained by the two polar solvents (A: deuterated phosphate buffer/methanol-d4, B: methanol-d4) show an individual marker signal (Extraction A: singlet at 3.05 ppm, extraction B: singlet at 3.02 ppm), which could indicate the admixture of peanut. The highlighted region showed the difference between peanuts and other nuts.
Source: Detection of Peanut Adulteration in Food Samples by NMR Spectroscopy. J. Agric. Food Chem.,• DOI: 10.1021/acs.jafc.0c01999
The above figure shows the variation of the peak at 3 ppm (Parts per million calibrated based on the frequency difference between the resonance of the sample and the reference compound) from which we can find this type of adulteration.
The IR (Infrared) specifically Mid-infrared (MIR) spectra are informative fingerprints of molecular vibrations and rotations within compounds. This spectral region typically ranges from approximately 4000 to 400 cm^-1. In MIR spectroscopy, molecules absorb radiation in the mid-infrared range, causing characteristic peaks in the spectrum corresponding to specific functional groups and chemical bonds. These peaks provide valuable information about molecular structure, composition, and interactions.
The following figure shows the M-IR spectra of milk showing different nutrients and edible biological molecules present in it. If more water or any other chemical is added to it the resulting spectra will be different.
Representative images of the mid-infrared spectrum of milk and the approximate putative region obtained with TQ Analyst software ver. 8.0 (Thermo Fisher Scientific, Madison, WI, USA).
Source: Recent Advances in the Determination of Milk Adulterants and Contaminants by Mid-Infrared Spectroscopy: Foods 2023, 12(15), 2917; https://doi.org/10.3390/foods12152917
The famous and widely used diagnostic tool MRI in the medical field is also a type of spectroscopy. It reveals the inner structure of the human body. It is a non-invasive medical imaging technique used to visualize the anatomy and pathology. MRI relies on the interaction of hydrogen nuclei (protons) in water and fat molecules with a strong magnetic field and radiofrequency pulses. By measuring the signals emitted by these nuclei, detailed images of the spinal cord can be generated.
The following image shows the MRI image of a patient which shows the anatomy and pathology of the spine and its surrounding structures.
Various orientations of spin were taken using an MRI.
X-ray crystallography is a powerful technique used to determine the three-dimensional structure of crystalline materials at the atomic level. X-ray crystallography relies on the interaction of X-rays with the electron density of atoms within a crystal lattice. When X-rays strike a crystal, they are diffracted by the regularly spaced atoms, producing a diffraction pattern of spots on a detector.
The following figure shows the x-ray peak of Maltose and Cocaine. As both of them are physically indistinguishable the XRD pattern of the compounds can be used to detect the presence of cocaine. The following shows the different peaks of the two compounds.
Simulated diffraction patterns of cocaine and maltose are displayed along with the peak positions of the International Centre for Diffraction Data (ICDD) standard. Two mixtures, 50% cocaine / 50% maltose and 10% cocaine / 90% maltose, show the qualitative differences in the XRD pattern as the components are varied. Qualitative identification is based on the presence of the unique diffraction lines for each substance, the "X-ray fingerprint." In addition, a quantitative determination can be made for each component by measuring its peak intensity and comparing it to the intensities measured from one or more samples of known concentration.
Source: FORENSIC ANALYSIS BY X-RAY DIFFRACTION: https://www.rigaku.com/applications/bytes/xrd/miniflex/1060214993
Concluding remarks:
Using a CD as a diffraction grating for spectroscopy is a fun and educational experiment that can be easily performed at home or in a classroom setting. It provides a hands-on way to explore the properties of light and learn about the principles of spectroscopy. Additionally, it highlights the versatility of everyday materials in scientific experimentation and encourages curiosity and exploration in the field of optics and spectroscopy.
In summary, understanding spectroscopy is crucial for advancing scientific knowledge, developing new technologies, improving healthcare outcomes, and addressing global challenges. It enriches our understanding of the natural world and empowers us to innovate and make informed decisions in both scientific and everyday contexts.
HOPE YOU LEARNT A NEW THING AND CHANGE THE WAY OF LOOKING AROUND YOU.
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