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class="visually-hidden focusable" data-elastic-exclude> Skip to main content </a> <div class="dialog-off-canvas-main-canvas" data-off-canvas-main-canvas>  <section data-elastic-exclude class="usa-banner" aria-label="Official government website"> <div class="usa-accordion"> <header class="usa-banner__header"> <div class="usa-banner__inner"> <div class="grid-col-auto"> <img class="usa-banner__header-flag" src="/web/20230830171939im_/https://www.nist.gov/libraries/nist-component-library/dist/img/us_flag_small.png" alt="U.S. flag"> </div> <div class="grid-col-fill tablet:grid-col-auto"> <p class="usa-banner__header-text">An official website of the United States government</p> <p class="usa-banner__header-action" aria-hidden="true">Here鈥檚 how you know</p> </div> <button class="usa-accordion__button usa-banner__button" aria-expanded="false" aria-controls="gov-banner-default"> <span class="usa-banner__button-text">Here鈥檚 how you know</span> </button> </div> </header> <div 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<span>Twitter</span> </a> </div> <div> <a href="https://web.archive.org/web/20230830171939/mailto:/?subject=NIST.gov&body=Check out this site https://www.nist.gov/pml/productsservices/physical-reference-data" title="Email" class="nist-social nist-social--envelope-gray"> <span>Email</span> </a> </div> </div> </div> </div>  </div> <div class="nist-block"> <div class="text-with-summary"> <p><strong><a href="https://web.archive.org/web/20230830171939/https://www.nist.gov/pml/elemental-data-index">Elemental Data Index</a></strong></p> <p>Provides access to the holdings of NIST Physical Measurement Laboratory online data organized by element.</p> <p><strong><a href="https://web.archive.org/web/20230830171939/https://www.nist.gov/pml/periodic-table-elements">Periodic聽Table: Atomic Properties of聽the聽Elements</a></strong></p> <p>Contains NIST critically-evaluated data on atomic properties of the elements.<br> Suitable for high-resolution color printing for desk or wall-chart display.<strong>聽</strong></p> <p><strong><a href="https://web.archive.org/web/20230830171939/https://www.nist.gov/pml/fundamental-physical-constants">Physical Constants</a></strong></p> <p>Contains values of the fundamental physical constants and a related bibliographic database.</p> <p><strong><a href="https://web.archive.org/web/20230830171939/https://www.nist.gov/pml/atomic-spectroscopy-databases">Atomic Spectroscopy Data</a></strong></p> <p>Contains databases for energy levels, wavelengths, radiative transition probabilities, and ionization energies for atoms and ions and related bibliographic databases.</p> <p><strong><a href="https://web.archive.org/web/20230830171939/https://www.nist.gov/pml/molecular-spectroscopic-data">Molecular Spectroscopic Data</a></strong></p> <p>Includes databases containing spectroscopic data for small molecules, hydrocarbons, and interstellar molecules. In addition, there are two publications containing equations and the underpinning theory for molecular spectroscopy.</p> <p><strong><a href="https://web.archive.org/web/20230830171939/https://www.nist.gov/pml/atomic-and-molecular-data">Atomic and Molecular Data</a></strong></p> <p>Contains databases on thermophysical properties of gases, electron-impact cross sections (of atoms & molecules), potential energy surfaces of group II dimers, and atomic weights and isotopic compositions.</p> <p><strong><a href="https://web.archive.org/web/20230830171939/https://www.nist.gov/pml/x-ray-and-gamma-ray-data">X-Ray and Gamma-Ray Data</a></strong></p> <p>Contains databases on the interaction of x-rays and gamma-rays with elements and compounds.</p> <p><strong><a href="https://web.archive.org/web/20230830171939/https://www.nist.gov/pml/radiation-dosimetry-data">Radiation Dosimetry Data</a></strong></p> <p>This database calculates stopping-power and range tables for electrons, protons, or helium ions.</p> <p><strong><a href="https://web.archive.org/web/20230830171939/https://www.nist.gov/pml/nuclear-physics-data">Nuclear Physics Data</a></strong></p> <p>Contains a table of the half lives of 65 radionuclides and a database of the isotopic compositions, atomic weights and relative atomic masses of the elements.</p> <p><strong><a href="https://web.archive.org/web/20230830171939/https://www.nist.gov/pml/condensed-matter-physics-data">Condensed Matter Physics Data</a></strong></p> <p>This database consists of evaluated data for use in total-energy calculations of electronic structure by density-functional theory. It contains total energies and orbital energy eigenvalues for all atoms from hydrogen to uranium.</p> <p><strong><a href="https://web.archive.org/web/20230830171939/https://www.nist.gov/srd">Other NIST Data</a></strong></p> <p>Provides access to all data sets at NIST.</p> <hr><p>The use of International Units and the expression of uncertainty in measurement is critical to all data activities. For information on these topics, see guidelines for <a href="https://web.archive.org/web/20230830171939/http://physics.nist.gov/cuu/Uncertainty/index.html">evaluating and expressing measurement uncertainty</a>, and information on the <a href="https://web.archive.org/web/20230830171939/http://physics.nist.gov/cuu/Units/index.html">International System of Units (SI)</a>.</p> </div> </div> <div class="nist-block">  <div data-elastic-exclude="" class="nist-tags"> <a href="/web/20230830171939/https://www.nist.gov/topic-terms/analytical-chemistry" hreflang="en">Analytical chemistry</a>, <a href="/web/20230830171939/https://www.nist.gov/topic-terms/atomic-molecular-quantum" hreflang="en">Atomic / molecular / quantum</a>, <a href="/web/20230830171939/https://www.nist.gov/topic-terms/condensed-matter" hreflang="en">Condensed matter</a>, <a href="/web/20230830171939/https://www.nist.gov/topic-terms/electron-physics" hreflang="en">Electron physics</a>, <a href="/web/20230830171939/https://www.nist.gov/topic-terms/nuclear-physics" hreflang="en">Nuclear physics</a>, <a href="/web/20230830171939/https://www.nist.gov/topic-terms/radiation" hreflang="en">Radiation</a>, <a href="/web/20230830171939/https://www.nist.gov/topic-terms/spectroscopy" hreflang="en">Spectroscopy</a> and <a href="/web/20230830171939/https://www.nist.gov/topic-terms/reference-data" hreflang="en">Reference data</a></div>  </div> </div> </div> </div> <div class="grid-container"> <div class="nist-page__region nist-page__region--content-bottom"> <div class="nist-block nist-block--contact"> <h2 class="nist-block__title">Contacts</h2> <div class="nist-contact"> <ul class="nist-contact__items"> <li class="nist-contact__item"> <div class="nist-contact__name"> PML webmaster </div> <div> <a href="https://web.archive.org/web/20230830171939/mailto:pml-webmaster@nist.gov">pml-webmaster@nist.gov</a> </div> <div> </div> </li> </ul> </div> </div> <div class="nist-block"> <div class="text-italic font-sans-2xs"> Created July 15, 2009, Updated June 2, 2021 </div> </div> </div> </div> </section> </div> <div data-elastic-exclude>  <footer class="nist-footer padding-bottom-4"> <div class="grid-container nist-footer__info"> <div class="grid-row"> <div class="tablet:grid-col-6"> <div class="nist-footer__logo"> <a href="/web/20230830171939/https://www.nist.gov/" title="National Institute of Standards and Technology" rel="home"> <img class="nist-footer__logo-img" src="/web/20230830171939im_/https://www.nist.gov/libraries/nist-component-library/dist/img/logo/NIST-Logo-Brand-White.svg" alt="National Institute of Standards and Technology logo" width="300px" height="42px"/> </a> </div> <div class="nist-footer__contact"> <h3 class="nist-footer__contact-heading">HEADQUARTERS</h3> <address> 100 Bureau Drive<br> Gaithersburg, MD 20899<br> <a href="https://web.archive.org/web/20230830171939/tel:301-975-2000">301-975-2000</a> </address> <p> <a href="https://web.archive.org/web/20230830171939/mailto:do-webmaster@nist.gov">Webmaster</a> | <a href="https://web.archive.org/web/20230830171939/https://www.nist.gov/about-nist/contact-us">Contact Us</a> | <a href="https://web.archive.org/web/20230830171939/https://www.nist.gov/visit">Our Other Offices</a> </p> </div> </div> <div class="tablet:grid-col-6"> <div class="nist-footer__social-links"> <a class="nist-social nist-social--twitter-white" href="https://web.archive.org/web/20230830171939/https://twitter.com/NIST"> <span>Twitter</span> </a> <a class="nist-social nist-social--facebook-white" href="https://web.archive.org/web/20230830171939/https://www.facebook.com/NIST"> <span>Facebook</span> </a> <a class="nist-social nist-social--linkedin-white" href="https://web.archive.org/web/20230830171939/https://www.linkedin.com/company/nist"> <span>LinkedIn</span> </a> <a class="nist-social nist-social--instagram-white" href="https://web.archive.org/web/20230830171939/https://www.instagram.com/nist/"> <span>Instagram</span> </a> <a class="nist-social nist-social--youtube-white" href="https://web.archive.org/web/20230830171939/https://www.youtube.com/NIST"> <span>YouTube</span> </a> <a class="nist-social nist-social--giphy-white" href="https://web.archive.org/web/20230830171939/https://giphy.com/nist"> <span>Giphy</span> </a> <a class="nist-social nist-social--rss-white" href="https://web.archive.org/web/20230830171939/https://www.nist.gov/news-events/nist-rss-feeds"> <span>RSS Feed</span> </a> <a class="nist-social nist-social--envelope-white" href="https://web.archive.org/web/20230830171939/https://public.govdelivery.com/accounts/USNIST/subscriber/new"> <span>Mailing List</span> </a> </div> <div class="nist-footer__feedback"> How are we doing? 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