What is Absorption spectrum: Definition and 29 Discussions

Absorption spectroscopy refers to spectroscopic techniques that measure the absorption of radiation, as a function of frequency or wavelength, due to its interaction with a sample. The sample absorbs energy, i.e., photons, from the radiating field. The intensity of the absorption varies as a function of frequency, and this variation is the absorption spectrum. Absorption spectroscopy is performed across the electromagnetic spectrum.
Absorption spectroscopy is employed as an analytical chemistry tool to determine the presence of a particular substance in a sample and, in many cases, to quantify the amount of the substance present. Infrared and ultraviolet–visible spectroscopy are particularly common in analytical applications. Absorption spectroscopy is also employed in studies of molecular and atomic physics, astronomical spectroscopy and remote sensing.
There are a wide range of experimental approaches for measuring absorption spectra. The most common arrangement is to direct a generated beam of radiation at a sample and detect the intensity of the radiation that passes through it. The transmitted energy can be used to calculate the absorption. The source, sample arrangement and detection technique vary significantly depending on the frequency range and the purpose of the experiment.
Following are the major types of absorption spectroscopy:

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  1. F

    Chemistry Why Do Sulfurous Compounds Show Different Peaks in X-ray Absorption Spectra?

    Hey guys :) actually my homework was just to research the absorption spectra of some iron compounds and some sulfurus compounds - to which I have the answer. I just dont understand it. In this arcticle, fig 2b: "Phase Composition of Iron Oxide Nanoparticles Studied Using Hard X-ray Absorption...
  2. D

    I Experimental demonstration of an absorption spectrum

    Hello, is there a convincing experiment to visualize absorption spectra? At disposal I have: - Halogen lamps - Lenses - Straight view prism - transmission grating - slit, iris, screen - Sodium vapor lamp and mercury vapor lamp Unfortunately, I do not have a sodium vapor cell or anything...
  3. C

    A Physical explanation of time-correlation function and spectrum

    From my reading of several quantum optics textbooks and spectroscopy texbooks, the emission and absorption spectrum of an atom or molecule are always given in terms of the time-correlation function, for example the emission spectrum of a two level atom is given by: $$...
  4. C

    A Absorption and emission spectrum in quantum optics

    The emission spectrum or resonance fluorescence for a quantum dot, atom or defect center are discussed in many quantum optics textbook, for example see "Quantum Optics" by Marlan O. Scully and M. Suhail Zubairy Chapter 10 , "Quantum Optics" by D. F. Walls and Gerard J. Milburn Chapter 10 and...
  5. S

    Absorption Spectrum Practice problem

    Summary: The experimentally measured absorption spectrum of 1,3-pentadiene molecule exhibits a peak absorption (light absorption) around 224 nm corresponding to an electronic transition. Estimate the length of the molecule. I thought of using lambert law A = c*l*e but we have none. how do I...
  6. Cool4Kat

    I Confusion about absorption spectra - cool gases absorb?

    So I was taught in school that heated low density gases produce spectral lines and cool low density gases absorb their spectral lines. I mentioned this to my husband and he asked me what the definition of hot and cool were and I had no idea. The more I thought about it, the more confused I...
  7. H

    Transition energy estimation based on bond length

    I come across this question in a textbook. Somehow my result is way off from the solution answer. I used the energy formula for particle in a box with n(Initial) = 22 and n(End) = 23, the calculated box length is 732 pm. I arrived at an answer of 39.3 nm. The answer from the answer book is but...
  8. Cardinalmont

    B Why are absorption spectra continuous?

    It doesn't make sense to me that absorption spectra are (mostly) continuous. Here are my beliefs. Please tell me which piece/pieces is a/are misconception(s). 1) When light is absorbed, the energy is used to excite an electron to some discrete energy level. 2) To get to this discrete energy...
  9. J

    A Subtract Radiated from Background Spectrum to Analyze Absorption Spectrum

    Hi everyone, I have an absorption spectrum that I obtained from a sample after radiation and I need to use the background sample as a reference, how can I do that using excel? what I did is subtract the radiated from the background spectrum then plot it, is that right? Thanks.
  10. E

    I Only certain emission lines show up in absorption spectrum

    I'm reading Eisberg's Modern Physics and in it, in the atomic spectra chapter, he says: "We have been discussing the emission spectrum of an atom. A closely related property is the absorption spectrum. This may be measured with apparatus similar to that shown in figure (5-1) except that a...
  11. K

    Sunlight absorption spectrum and colors in sunlight

    Hi. In physics articles, they say that sun light is white, and contain all colors. But they show say that the Sun's atmosphere absorb light at certain wavelengths, causing the intensity of the light at this wavelength to drop and appear dark. And the absorption spectrum looks like this...
  12. Clara Chung

    B Line absorption spectrum and stars

    Why can't hydrogen gas on the stars be detected by using line emission spectrum of hydrogen. Why must we use line absorption spectrum to detect?
  13. L

    Molecular Hydrogen absorption spectrum

    Is it true, as someone says, that molecular hydrogen in its fundamental state don't (almost?) absorb in the frequencis of the Balmer series of atomic hydrogen emission spectrum? Thanks. -- lightarrow
  14. F

    Bradford dye absorption spectrum question?

    https://www.physicsforums.com/attachments/74483 https://www.physicsforums.com/attachments/74483 Based in the absorption spectra above, why is 595 nm the best wavelength to measure protein concentration with Bradford dye (Hint: there are two important reasons for choosing 595). I think it has...
  15. U

    How Is the Rydberg Constant Calculated from Photon Absorption Wavelengths?

    Homework Statement The following photon wavelengths are observed in absorption at room temperature from an ionized atomic gas with a single electron orbiting the nucleus: λ= 13:5 nm, 11:4 nm, 10:8 nm. Use this data to determine the effective Rydberg constant and the nuclear charge...
  16. F

    Quantum dots:emission versus absorption spectrum

    Hello Forum, how is is possible for quantum dots to offer a wide, broadband absorption spectrum but still have a single distinct emission wavelength? How is that asymmetry possible? For example, I would think that if we can absorb, say, 4 wavelengths, we can also emit those say 4...
  17. P

    Finding a light source that produces an absorption spectrum?

    This is an observational exercise where I have to find several different light sources and observe their spectra through a diffraction grating, then record my observations. I need two sources of each (i.e. continuous, emission, absorption). Continuous and emission are fairly easy, but for the...
  18. L

    Emission or absorption spectrum

    Homework Statement X rays give continuous spectrum and line spectrum. Whether these spectrums are emission or absorption spectrum? Homework Equations The Attempt at a Solution I think it is emission spectrum, because there is no absorbing material. Still, i need confirmation from...
  19. H

    Infrared absorption spectrum of CO2 at 4,3 µm

    Hello! I'm writing a thesis about the optical properties of CO2. However I'm having a hard time finding any solid material about the basic info of the absorption spectrum of CO2. I'm especially interested in the absorption band at approximately 4,3µm. If any of you guys know some good articles...
  20. L

    Continuous absorption spectrum - why this happens?

    Continuous absorption spectrum -- why this happens? Homework Statement A pure green glass plate placed in the path of light, absorbs everything everything except green, similarly red glass plate absorbs everything except red. Homework Equations May i know the reason for this? Thanks...
  21. L

    Continuous absorption spectrum

    Homework Statement While dealing with continuous absorption spectrum, my book depicts like this " A pure green glass plate when placed in the path of white light, absorbs everything except green and gives continuous absorption spectrum" Homework Equations The Attempt at a Solution...
  22. J

    Does the CMBR have a detectable absorption spectrum?

    I posted this http://answers.yahoo.com/question/index;_ylt=AioiPKUALWyrKuH4dGXejba9DH1G;_ylv=3?qid=20110618143816AAgRMyF"on Yahoo Answers yesterday, but it might be too specialized: If I understand correctly, the Cosmic Microwave Background Radiation is a perfect thermal (black-body)...
  23. V

    Understanding the Gap in a HCl Absorption Spectrum

    Looking at a HCl spectrum (from hyerphysics: http://hyperphysics.phy-astr.gsu.edu/hbase/molecule/vibrot.html), I don't understand why there is a gap in the middle of the spectrum that seems to act as a line of symmetry in the x-axis. Can anyone help please?
  24. A

    Absorption Spectrum of Hydrogen

    When white radiation is passed through a sample of hydrogen gas(atoms assumed actually) why are absorption lines observed in Lyman series only? The corresponding photon energy range for visible light(380-780nm) are 1.59-3.27eV which should cause transitions of electrons in the first excited...
  25. J

    Explaining the Unexpected Spikes in a Quantum Well Absorption Spectrum

    I'm looking in a textbook at a discussion of a semiconductor quantum well which is being irradiated and an absorption spectrum produced. Electrons are being promoted across the band gap and holes are being created. There are heavy hole and light hole transitions, and the spectrum shown rises in...
  26. M

    Questions re: absorption spectrum

    Hi readers, I'm confused about some aspects of absorption spectroscopy, and hoping someone can de-confuse me First, just a preliminary question; am I right in thinking that when an electron absorbs a photon, the electron will then emit a photon of the same frequency and energy as the one...
  27. A

    Absorption spectrum in chlorophyll

    I have a question. We claim that the wavelength of a photon must exactly match the difference between the states of an atom or molecule. Then why are the peaks in the absorption spectrum of chlorophyll so broad? Shouldn’t they be very sharp?
  28. 3

    Absorption spectrum of water in the UV range

    Hi all, I have not seen a separate section for photonics, so I'll post my question here : Does anyone have measurement data of the absorption spectrum of (liquid) water in the wavelength range of 180 - 250 nm ? Thanks :smile:
  29. Q

    Absorption Spectrum and Temperature

    I'm going through some notes and came upon a question... So, the absorption sepctrum can be seen when a gas sample is placed in the path of white incandescent light where the light absorbes descrete wavelengths. I read that only some of these absorption lines appear if the gas is cool, but...