What Is The Energy Of A Single Infrared Photon
Photon energy is the energy carried by a single photon. The amount of energy is directly proportional to the photon's electromagnetic frequency and thus, equivalently, is inversely proportional to the wavelength. The higher the photon's frequency, the higher its energy. Equivalently, the longer the photon's wavelength, the lower its energy.
what is the energy of a single infrared photon
Photon energy can be expressed using any unit of energy. Among the units commonly used to denote photon energy are the electronvolt (eV) and the joule (as well as its multiples, such as the microjoule). As one joule equals 6.24 1018 eV, the larger units may be more useful in denoting the energy of photons with higher frequency and higher energy, such as gamma rays, as opposed to lower energy photons as in the optical and radio frequency regions of the electromagnetic spectrum.
Very-high-energy gamma rays have photon energies of 100 GeV to over 1 PeV (1011 to 1015 electronvolts) or 16 nanojoules to 160 microjoules. This corresponds to frequencies of 2.42 1025 to 2.42 1029 Hz.
Note that as the wavelength of light gets shorter, the energy of the photon gets greater. The energy of a mole of photons that have the wavelength λ is found by multiplying the above equation by Avogadro's number:
In the lesson on atmospheric composition, you saw how solar UV radiation was able to break apart molecules to initiate atmospheric chemistry. These molecules are absorbing the energy of a photon of radiation, and if that photon energy is greater than the strength of the chemical bond, the molecule may break apart.
Need a quick unit conversion from wavelength (nm) to photon energy (eV)? Need to convert flux (ph/s) to average power (mW)? Simply enter the known value in the boxes below, and the calculator will provide the equivalent value in the appropriate unit.
Power (P) is the rate of energy transfer with the SI unit of 1 Watt = 1 J/s. The power of short wavelength light sources in the EUV to X-ray range are often expressed as photon flux (F) in the units of photons per second (ph/s). Average power is related to flux and photon energy by:
Molecules of carbon dioxide (CO2) can absorb energy from infrared (IR) radiation. This animation shows a molecule of CO2 absorbing an incoming infrared photon (yellow arrows). The energy from the photon causes the CO2 molecule to vibrate. Some time later, the molecule gives up this extra energy by emitting another infrared photon. Once the extra energy has been removed by the emitted photon, the carbon dioxide molecule stops vibrating.
This animation is somewhat of a simplification. Molecules are constantly in motion, colliding with other gas molecules and transferring energy from one molecule to another during collisions. In the more-complex, real-world process, a CO2 molecule would most likely bump into several other gas molecules before re-emitting the infrared photon. The CO2 molecule might transfer the energy it gained from the absorbed photon to another molecule, adding speed to that molecule's motion. Since the temperature of a gas is a measure of the speed of the molecules in the gas, the faster motion of a molecule that eventually results from the IR photon that was absorbed by a CO2 molecule raises the temperature of the gases in the atmosphere.
This ability to absorb and re-emit infrared energy is what makes CO2 an effective heat-trapping greenhouse gas. Not all gas molecules are able to absorb IR radiation. For example, nitrogen (N2) and oxygen (O2), which make up more than 90% of Earth's atmosphere, do not absorb infrared photons. CO2 molecules can vibrate in ways that simpler nitrogen and oxygen molecules cannot, which allows CO2 molecules to capture the IR photons.
Radiation is a form of energy transport. Electromagnetic energy (radiation) is composed of individual "packets" or "particles" of energycalled photons. A photon is the smallest amount of radiation energy that can exist, i.e., photonscannot be broken down. Photons are classified by the amount of energy they carry. Some of thedifferent types of radiation you may have heard of include X-ray, ultraviolet, visible, infrared,and microwave among others. The list was given in order of decreasing photon energy, i.e., anultraviolet photon carries more energy than a visible photon, which carries more energy than aninfrared photon, etc. Natural radiation is emitted (or given off) by all objects. The hotteran object, the more energetic photons it emits. For example, the hot sun emits ultraviolet, visible,and infrared photons (billions upon countless billions of individual photons), while the colder objects on Earth (the ground, oceans, trees, you) do notemit ultraviolet or visible photons, only infrared photons. Our eyes cannot see infrared photons,such as those emitted by relatively cold objects on the Earth (includes emission from ground surface,human beings, etc.), but we can see visible photons coming from the Sun. In fact most of the radiation emitted by the Sun is in the form of visible photons. However, the Sun also emits significant radiation energy in the form of ultaviolet photons that cannot be seen by our eyes,but can be dangerous to us.
Some of you may be more familar with using the electromagnetic wavelength to define different typesof radiation. I thought the photon concept would be easier for most students. In terms of wavelength,ultraviolet radiation has shorter wavelengths than visible radiation, which have shorter wavelengths than infrared.Ultraviolet range of wavelength (0.01-0.4 micrometers); Visible range of wavelength (0.4-0.7 micrometers);Infrared range of wavelengths (0.7-100 micrometes). You will not have to know this wavelength informationfor the exam. What I would like you to know is that a single photon of ultraviolet radiation carriesmore energy than a single photon of visible radiation which carries more energy than a single photon of infrared radiation.
An object absorbs radiation energy by absorbing photons. This is how energy is transferred by radiation. One object emits or gives off radiation energy (photon by photon) and that energy is delivered to anotherobject when that object absorbs radiation energy (photon by photon). Ultraviolet photons have enough energy todissociate molecules, visible and infrared photons do not. For example, when ozone (O3) absorbs ultravioletradaition, the molecule is split leaving (O2) and (O). Of more importance to us,ultraviolet photons have enough energy to damage or destroy DNA, visible and infrared photons do not. Whenwe absorb visible or infrared photons the energy carried by the photon goes into heating us up, but will notpermanently damage our cells like ultraviolet photons can. See this WORD document summarizing uv radiation.
Each of the classes of radiation is defined over a range of photon energies. For example, within visiblelight, a "blue" photon carries more energy than a "red" photon. In the same way ultraviolet radiation isfurther divided into 3 categories:UV-C (wavelengths 0.2-0.29 micrometers)
most energetic and potentially damaging to cells
virtually all UV-C from Sun is absorbed by O3 and O2 in the stratosphere (and below)and does not reach the surface
UV-B (wavelengths 0.29-0.32 micrometers)
Most UV-B from the Sun is absorbed by O3 in the stratosphere, but a significant portiondoes penetrate to the ground
Linked to about 90% of skin cancers
Also responsible for sunburns, eye cataracts, photoaging (wrinkling of skin), suppression of the immune system, and other problems in humans
Reduces growth and health of ocean phytoplankton, damages early development in some fish, shrimp, and amphibians
Damages and stresses many land plants including some staple food crops
UV-A (wavelengths 0.32-0.40 micrometers)
Least energetic type of ultraviolet photon
But long-term exposure can lead to skin damage, such as photoaging (wrinkling or "leathery" skin) and perhaps skin cancer (not proven)
Thus, you can see that ultraviolet radiation can be quite harmful to both humans and other inhabitants of the Earth.This is why we should be so concerned about any depletion of stratospheric ozone. But before moving on, I should mentionthat some ultraviolet radiation is beneficial to us. It stimulates the body to produce vitamin D. In a place like Tucson,there is enough stray ultraviolet radiation (that reflected off other surfaces and not in the direct beam of the Sun) forplenty of vitamin D production, however, lack of ultraviolet exposure resulting in vitamin D deficiencies can be a problem for people living in high latitude regions, especiallyin winter. In addition, ultraviolet radiation may be responsible for random mutations in organisms, some of which lead toevolutionary speciation.
Most tissues have the capacity to absorb light energy. Usually this is mediated by a molecule absorbing a photon. Molecules containing metal ions have a strong capacity for absorbing photonic energy, but DNA and water also can. The absorption of energy can induce a change in the confirmation and/or function of the molecule.
Penetration of NIR through tissues is determined by several factors: wavelength, energy, attenuation coefficient (composed of scatter, refraction, and absorption), area of irradiance, coherence, and pulsing. In general, longer wavelengths (up to 1,000 nm) will penetrate deeper; however, the absorption of water begins to predominate above 1,000 nm.96 Increases in power density, in general, will lead to greater penetration. More photons will traverse the tissue. The area of surface irradiation also affects penetration due to scattering effects.
Notes: (A) The pad of LEDs is held 2 mm from the surface of the light meter detector. The arrow indicates a row of near-infrared light (NIR) LEDs with a wavelength of 880 nm. The meter reads 0.01 W. (B) Human skin 1.9 mm thick is interposed between the NIR LED and the light meter detector. Thin plastic wrap covers the detector. (C) The NIR LED is covered with thin plastic wrap and placed directly against the sample of human skin. Photonic energy could not be detected passing through 1.9 mm of human skin.